Questions and Answers about COVID-19 Vaccines

On this page, you will find answers to some of the most common questions people are asking about COVID-19 disease and vaccines. Just click on the question of interest and the answer will appear below it. 

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If young children do not get severely ill from COVID-19, why should I consider giving this vaccine to my child who is younger than 5 years of age?

As parents weigh the relative risk and benefits of getting their youngest children vaccinated against COVID-19, some wonder about the need for their child to get a relatively new vaccine when the disease doesn’t seem too bad in most children. Most healthcare providers agree that the benefits of vaccination outweigh the risks for our youngest family members:

  • As of June 2022, almost 1,500 children 17 years of age or younger have died from COVID-19. While this is a very small number compared with the more than 1 million deaths in the U.S., for those approximately 1,500 families, their world will never be the same.
  • During the past two years, about 45,000 children less than 5-years of age have been hospitalized with COVID-19, about 10,000 have been admitted to the intensive care unit, and about 450 have died from the disease.
  • Millions of children have been infected with the virus that causes COVID-19. Some of those children were hospitalized with severe disease or developed a condition called multi-inflammatory syndrome in children (MIS-C), which can damage organs and on rare occasions be deadly.
  • Like adults, some children who have had COVID-19, even mild cases, have experienced lingering symptoms, commonly referred to as “long COVID.” In younger children it may be difficult for them to express what they are feeling or experiencing, which can make this condition even more difficult to identify and address.
  • While the vaccine was just approved in young children, millions of vaccines using this same approach at higher doses have been administered at this point. Given that the doses for children less than 5 years of age are lower, it would be unlikely that previously uncovered side effects would emerge. Likewise, more severe side effects found in other groups, like myocarditis, were not experienced in the studies completed in this age group. This said, we need to continue to monitor whether myocarditis occurs when more children are vaccinated. Even if it were found to occur in rare instances, it would be expected to occur similarly to that seen after vaccination of other groups in which the myocarditis after vaccination is less severe and of shorter duration than that which occurs after infection.

To see what others are saying, check out these videos that include clinicians, polio survivors, and families affected by influenza, another disease often thought to be “not too bad.”

Last updated: June 20, 2022

What is the Novavax vaccine and who can get it?

The Novavax COVID-19 vaccine uses a “tried and true” approach to inducing immunity. Specifically, the vaccine delivers the spike protein and an adjuvant, which is something that increases immune responses to the protein. It is given as two doses, separated by 3-8 weeks, to those 18 years of age and older. This technology is exactly the same as that used to make one of the influenza vaccines (FluBlok) and very similar to that used to make the hepatitis B and human papillomavirus vaccines.

To find out more about the Novavax vaccine, watch this video of VEC Director, Paul Offit, MD, who is on the FDA’s advisory committee and, therefore, reviewed the data presented during the advisory committee meeting.

Last updated: July 21, 2022.

If my child previously received two doses of COVID-19 vaccine, should they get a booster dose or wait until fall?

Many families are trying to determine whether to get their children boosted at this point or wait until the fall. Booster doses increase the antibodies circulating in the blood for about three to six months, decreasing the chance of any infection during that time.

Pfizer vaccine

  • Children 6 months to 4 years of age are recommended to get three doses of vaccine. All three doses are part of the “primary series,” meaning that the child needs all three doses to have the best protection. No booster doses are recommended for this age group at this time.

Children 5 years of age and older are recommended to get two or three “primary doses” of Pfizer’s vaccine, depending on their immune status. They can also get a single booster dose either 3 or 5 months after their last dose, depending on their immune status. Children 12 to 17 years of age who are immune compromised may be recommended to get a second booster dose four months after the first booster dose.

Moderna vaccine

  • Children 6 months to 17 years of age are recommended to get two or three primary doses of vaccine, depending on their immune status. For children without immune-compromising conditions, two doses are necessary for the best protection. For those with immune-compromising conditions, three doses are necessary for the best protection. No booster doses are recommended at this time.

Because it takes times for immunity to develop and because the current vaccines are still effective at protecting against severe disease, children who have not been vaccinated should start the series as soon as feasible in anticipation of returning to classrooms and activities this fall.

For children who have received the recommended primary doses of mRNA vaccine and were subsequently infected, a booster dose of vaccine is probably unnecessary.

For children who recently had COVID-19 disease, vaccination may be delayed for up to three months as they will be less susceptible to reinfection during that time and evidence suggests that they will develop a better immune response if there is more time between their illness and receipt of the vaccine. With this said, there is still a benefit to having children who were previously infected with COVID-19 vaccinated because the resulting immunity appears to be stronger than following either infection or vaccination alone.

Last updated: July 21, 2022

My teen is a student-athlete and already had COVID-19, so does he need the COVID-19 vaccine? We are worried about myocarditis.

While myocarditis is rare, it is also real; so, we can understand why some parents may be hesitant to get their teens vaccinated. But it is important when making these decisions to realize that the choice not to vaccinate is also a choice to risk COVID-19, so let’s take a look.

Square photo of myocarditis and teens infographic Check out this infographic [PDF, 126KB] to see a visual representation of this information. Imagine that the entire population of Roanoke, Virginia, (approximate population of 100,000 people) was composed of 16- to 29-year-old males:

  • If all of them were vaccinated, 5 of them would be expected to experience myocarditis following vaccination. (MMWR, Aug. 13, 2021 and NEJM, Dec. 2, 2021)
  • If none of them were vaccinated, 960 would be expected to get COVID-19, 30 of those infected would be hospitalized, 6 of those hospitalized would end up in the ICU, and 59 would be expected to experience myocarditis caused by COVID-19. (MMWR, Aug. 13, 2021 and MMWR, Sept. 3, 2021)

The rates of myocarditis following vaccination of females are significantly lower. If Roanoke was filled with 16- to 29-year-old females, only 1 of the vaccinated group would be expected to experience myocarditis. On the other hand, if none of them were vaccinated, 1,280 would be expected to get COVID-19, 75 of those infected would be hospitalized, 5 of those hospitalized would end up in the ICU, and about 39 would experience myocarditis caused by COVID-19.

It is also important to realize that myocarditis following vaccination is short-lived and tends to resolve on its own, whereas myocarditis following an infection tends to be more severe.

Three other considerations are important when deciding about COVID-19 vaccination of teens (or teen athletes):

  1. Data are emerging that vaccination following infection improves immunologic memory, so a previously infected, unvaccinated individual may be more likely to experience re-infection than a previously infected, vaccinated individual. And there is no evidence that myocarditis occurs more commonly following vaccination of those previously infected.
  2. We are still learning about “long COVID,” the condition that causes people to experience symptoms well after their infection goes away. While we don’t yet know how often this occurs in younger people, it is clear that some young people suffer similar long-term consequences.
  3. Finally, while not a biological consideration, if the concern is that student-athletes are able to participate, particularly in their Junior and Senior seasons, it is worth considering that student-athletes who remain unvaccinated may lose opportunities to participate if mandates for school attendance are put into place.

Click here to view a full-size image of the infographic [PDF, 126KB].

With all of this said, the CDC has increased the interval between dose 1 and dose 2, so that individuals, particularly young men up to 39 years of age, can delay the second dose up to 8 weeks to decrease the likelihood of experiencing myocarditis. Individuals who receive the Pfizer vaccine should get the second dose between 3 and 8 weeks later, and those who receive the Moderna vaccine should get the second dose between 4 and 8 weeks later. 

Last updated: June 20, 2022

Can someone with COVID-19 get the COVID-19 vaccine or booster?

In the U.S., the CDC recommends waiting until COVID-19 symptoms go away and the individual is done isolating. They also indicate that while it is okay to get the COVID-19 vaccine or booster shortly after recovering from the disease, individuals may want to delay getting their vaccine or booster for about three months after onset of symptoms or positive COVID-19 test. Individuals are less likely to be infected again during this period, and emerging evidence suggests that immune responses to the vaccine may be somewhat stronger. However, if an individual wants to get the vaccine sooner or if circumstances might preclude them from doing so later, they can proceed with vaccination once their isolation is complete.

Likewise, while the CDC previously recommended delaying vaccination for patients who were treated with antibody-based therapies, data now demonstrate that the modest reduction in antibody responses seen in these patients does not warrant the delay. With this said, most recently infected individuals are still recommended to wait for about three months before getting vaccinated, so the antibodies introduced by treatment are unlikely to be problematic anyway.

One stipulation that the CDC does recommend about antibody-based products relates to tixagevimab/cilgavimab (EVUSHELD™). If a patient recently received a COVID-19 vaccine, they should not receive tixagevimab/cilgavimab until two weeks after vaccination.

Last updated June 20, 2022

Why are booster doses recommended?

The goal of vaccination is to prevent serious illness. This is achieved by generating immune memory cells, such as B cells and T cells. These cells are typically long-lived and reside in the bone marrow, bloodstream, and lymph glands to monitor for exposure to a pathogen. If the pathogen is detected, these memory cells quickly become activated and stimulate the immune response to efficiently fight the infection before the infection can get out of control and cause serious illness. In the case of COVID-19 mRNA vaccines, studies demonstrated that high levels of memory cells are generated, and as the delta and omicron variants have emerged, we have seen that the levels of memory cells generated by both the mRNA (Pfizer and Moderna) and adenovirus-based (J&J/Janssen) vaccines have been sufficient to prevent serious illness in most cases. As such, these findings would not warrant a booster dose. 

However, a second goal of vaccination could be to prevent any level of illness, meaning that vaccinated people would not even experience mild or asymptomatic infection. To accomplish this, people need to have high levels of neutralizing antibodies circulating in their bloodstream. Neutralizing antibodies prevent the virus from attaching to and entering cells. Typically, neutralizing antibody levels fade over time. When this happens, a booster dose can stimulate the memory B and T cells to cause production of neutralizing antibodies, thereby increasing the level of detectable antibodies in the bloodstream and decreasing the chance for any level of illness.

While prevention of any level of illness is a noble goal, historically, prevention of serious illness has been the goal of vaccination, particularly for respiratory infections, like COVID-19. These two goals have been at the heart of the scientific “debate” over the need for booster doses.

Watch a video of Dr. Offit discussing the decision to recommend booster doses.

Last updated: Jan. 20, 2022; reviewed June 20, 2022

Do I need another dose of the COVID-19 vaccine?

Recommendations for additional doses of COVID-19 vaccine are based on an individual’s immune status, age, and type of COVID-19 vaccine(s) received previously.

Additional doses of COVID-19 vaccine may be recommended for one of two reasons:

  • To address waning immunity, traditionally called a booster dose.
  • To enhance the immune response of an individual who did not develop sufficient immunity following receipt of the recommended number of doses of COVID-19. In this case, the third dose can be considered as an additional primary dose. This most often occurs in individuals with a moderate or severe degree of immune compromise.

How the additional doses are implemented will be affected by which of these reasons are the cause for the recommendation. Individuals are recommended to get mRNA vaccines over J&J/Janssen when possible. Likewise, all primary doses should be with the same brand of vaccine whenever possible.

J&J/Janssen adenovirus vector vaccine

No immune-compromising condition

  • People who are not immune compromised and received the J&J/Janssen vaccine should get a second dose of vaccine separated by at least 8 weeks. The second dose is preferred to be an mRNA version.
  • If the individual is 50 years of age or older, they are recommended to get a third dose (mRNA version) at least 4 months after the previous dose.
  • Those 18- to 49-years of age whose first two doses were J&J/Janssen can opt for a third dose (mRNA version) at least 4 months after the most recent dose.

Immune-compromising condition

  • People considered to have moderate or severe immune compromising conditions who received the J&J/Janssen vaccine should get a second primary dose (mRNA version) at least 28 days after the first dose.
  • These individuals can get up to two booster doses with the first booster being given at least 8 weeks after the second dose and the second booster dose being given at least 4 months after the first booster dose.

Pfizer mRNA vaccine

No immune-compromising condition

  • 6 months to 4 years of age: Three doses of age-appropriate product (maroon-colored cap). Doses 1 and 2 should be separated by 3 to 8 weeks, and doses 2 and 3 should be separated by at least 8 weeks. Children need all three doses to complete the primary series (i.e., none of these doses are considered booster doses). These individuals would not be considered immune until 2 weeks after receipt of the third dose. The dose for this age group is one-tenth that of the adult Pfizer dose.
  • 5 years and older: All are recommended to get at least 3 doses of age-appropriate product (5- to 11-year- olds, orange cap; 12 and older, purple or gray cap). Doses one and two should be separated by 3 to 8 weeks; these are both considered primary doses. A third dose (booster) should be given at least 5 months after the second dose. The dose for those 5 to 11 years of age is one-third that of the adult Pfizer dose.
  • 50 years and older: Recommended to get a fourth dose (second booster) at least 4 months after receipt of the third dose.

Immune-compromising condition

  • 6 months to 4 years of age: Three doses of age-appropriate product (maroon-colored cap). Doses 1 and 2 should be separated by 3 weeks, and doses 2 and 3 should be separated by at least 8 weeks. Children need all three doses to complete the primary series (i.e., none of these doses are considered booster doses). These individuals would not be considered immune until 2 weeks after receipt of the third dose. The dose for this age group is one-tenth that of the adult Pfizer dose.
  • 5 years and older: All are recommended to get at least 4 doses of age-appropriate product (5- to 11-year- olds, orange cap; 12 and older, purple or gray cap). Doses one and two should be separated by 3 weeks; doses two and three should be separated by at least 4 weeks. All three of these doses are considered primary doses for those with immune-compromising conditions. A fourth dose (booster) should be administered at least 3 months after the third dose. The dose for those 5 to 11 years of age is one-third that of the adult Pfizer dose.
  • 12 years and older: Recommended to get a fifth dose (second booster) at least 4 months after receipt of the fourth dose.

Moderna mRNA vaccine

No immune-compromising condition

  • 6 months to 17 years of age: Two doses of age-appropriate product should be separated by 4 to 8 weeks. Children need both doses to complete the primary series (i.e., none of these doses are considered booster doses). These individuals would not be considered immune until 2 weeks after receipt of the second dose. The dose for this age group is one-fourth that of the adult Moderna dose.
  • 18 years and older: All are recommended to get at least three doses. Doses one and two should be separated by 4 to 8 weeks; these are both considered primary doses. A third dose (booster) should be given at least 5 months after the second dose. Booster doses of the Moderna vaccine should be half dose quantities compared with primary doses.
  • 50 years and older: Recommended to get a fourth dose (second booster) at least 4 months after receipt of the third dose.

Immune-compromising condition

  • 6 months to 17 years of age: Three doses of age-appropriate product should be administered. Doses one and two should be separated by 4 weeks, and doses two and three should be separated by at least 4 weeks. Children with immune-compromising conditions need all three doses to complete the primary series (i.e., none of these doses are considered booster doses). These individuals would not be considered immune until 2 weeks after receipt of the third dose. The dose for this age group is one-fourth that of the adult Moderna dose.
  • 18 years and older: All are recommended to get at least five doses. Doses one and two should be separated by 4 weeks. The third dose should be given at least 4 weeks after the second dose. All three of these are considered primary doses. A fourth dose (booster) should be given at least 3 months after the third dose, and a fifth dose (booster), given at least 4 months after the fourth dose. Booster doses of the Moderna vaccine should be half dose quantities compared with primary doses.

Novavax protein-based vaccine

No immune-compromising condition

  • 18 years and older: All are recommended to get two doses, separated by 3 to 8 weeks. Both doses are primary doses. No booster doses are recommended at this time.

Immune-compromising condition

  • 18 years and older: All are recommended to get two doses, separated by 3 weeks. Both doses are primary doses. No booster doses are recommended at this time.

For an overview chart, see the CDC’s “At-a-glance COVID-19 vaccination schedule.”

Immune-compromised individuals

People should talk with their healthcare providers to determine whether they are considered moderately or severely immune compromised since each individual is unique. However, the CDC has provided some guidance that may help.

People typically considered moderately or severely immune compromised include the following:

  • People currently being treated for cancers of the blood or organs (so-called “solid tumor” cancers)
  • People who received an organ transplant and take immunosuppressive medications to prevent rejection of the organ
  • People who had a stem cell transplant or received CAR-T-cell therapy less than 2 years ago or who are taking immunosuppressive medications
  • People with conditions that are considered to cause permanent immune deficiency because the condition affects cells of their immune system, such as DiGeorge syndrome or Wiskott-Aldrich syndrome
  • People infected with HIV whose infection is untreated or considered to be at an advanced stage
  • People currently being treated with one of the following types of medications:
    • High-dose corticosteroids (more than 20 mg prednisone or similar medications per day)
    • Alkylating agents
    • Antimetabolites
    • Transplant-related immunosuppressive medications
    • Cancer chemotherapeutic medications that are considered severely immunosuppressive (e.g., tumor-necrosis, or TNF, blockers)
    • Biologic agents that suppress or modulate the immune response

People who should work with their healthcare provider to determine their need for additional doses include:

  • People taking medications that make them uncertain whether they would be included in the list of individuals mentioned above
  • People with immune-system-related conditions not specifically mentioned above
  • People preparing to start one of the above-mentioned medications

People not considered to be in this category include:

  • People who do not have compromised immunity.
  • People without a spleen.
  • People who had cancer but are no longer being treated.
  • People with chronic conditions that do not involve the immune system or require treatment with high doses of corticosteroids, such as diabetes, asthma, COPD, kidney disease, heart conditions, sickle cell disease, among others. If you are not sure, check with your healthcare provider.

Last updated: July 21, 2022

Can I get my flu vaccine at the same time as my COVID-19 vaccine?

Yes. The CDC has indicated that people can get influenza vaccine and COVID-19 vaccine during the same visit, but in different locations, such as one in each arm or separated by at least one inch on the same arm. However, for those who are willing to come back to get one of the vaccines, it is prudent to wait two weeks between getting an influenza or COVID-19 vaccine. This way if there is a safety concern, it would be clear which vaccine might have caused the problem.

Last updated: Oct. 11, 2021; reviewed June 21, 2022

Can children get other vaccines at the same time as their COVID-19 vaccine?

Yes. The CDC has indicated that COVID-19 vaccine can be administered at the same visit as any other vaccines. However, the vaccines should be given in different locations separated by at least one inch. Because data related to COVID-19 vaccine receipt at the same time as other vaccines are limited, parents and healthcare providers may opt to give the vaccines on different days. Providers and parents should consider the likelihood that the child will be able to return for another visit without risk of falling behind on vaccinations, the child’s chance for exposure, and whether they have health conditions that increase their risk of experiencing severe disease if infected.

Last updated: June 21, 2022

What is the difference between emergency use authorization and the normal process of vaccine approval?

The main difference between emergency use authorization, or EUA, and the normal process, which is via a biologic licensure application, or BLA, is how long data were collected prior to the vaccines being reviewed for use. So, when considered quite literally, the vaccines being used under EUA are no different than those that are used after the vaccines get full approval (BLA). The reason for the shortened timeline was, of course, because of the pandemic. But, at this point, the vaccines have been given safely to millions of people and the companies have been monitoring vaccine recipients for months.

Last updated: Jan. 20, 2022; reviewed June 21, 2022

Were the COVID-19 vaccines approved by the FDA?

Even though the COVID-19 vaccines were initially released under Emergency Use Authorization (EUA), they were still approved by the Food and Drug Administration (FDA). The review process was the same, but because of the pandemic, the data could be submitted after a shorter period of participant follow-up than usual. However, even after submitting data (and getting an EUA), those studies continued. Pfizer’s vaccine has now been licensed for those 12 years of age and older, and Moderna’s, for those 18 years and older.

Last updated: July 21, 2022

Is it safe for my teen to get the COVID-19 vaccine given the stories about myocarditis?

Cases of myocarditis, or inflammation of the heart, have been reported in a small number of people after receipt of the COVID-19 mRNA vaccine:

  • The cases of myocarditis occur more often in boys and young men and more often after the second dose. Symptoms typically occur within 4 days after receipt of the dose. Recently immunized teens and young adults who experience chest pain or shortness of breath should be seen by a healthcare provider and report recent their vaccination.
  • Myocarditis is somewhat common, particularly following viral infections. In fact, cases tend to occur more often in the spring due to viruses that circulate at this time of year (specifically, coxsackie B viruses). Typically, about 100-200 cases occur per million people per year.
  • Available data suggest that the incidence of myocarditis following mRNA vaccines is about 1 per 50,000 vaccine recipients; however, this risk increases in males between 16 and 29 years of age to about 1 per 20,000 vaccine recipients. Of interest, myocarditis also occurs more commonly after either acute COVID-19 or as part of the multisystem inflammatory syndrome of children (MIS-C). For example, if 100,000 males between 16 and 29 years of age got the mRNA vaccine, about 5 would experience myocarditis. However, if 100,000 males between 16 and 29 years of age were infected with the virus that causes COVID-19, about 59 would experience myocarditis. These numbers are lower in females (See “My teen is a student-athlete and already had COVID-19, so does he need the COVID-19 vaccine?” for more detailed information or check this infographic.)
  • Parents and teens should watch for symptoms that may include chest pain, pressure, heart palpitations, difficulty breathing after exercise or lying down, or excessive sweating. One or more of these symptoms may also be accompanied by tiredness, stomach pain, dizziness, fainting, unexplained swelling, or coughing. If a recently vaccinated teen develops these symptoms or you are unsure, contact the child’s doctor or seek more immediate medical assistance if needed.
  • Of note, following the administration of Pfizer’s vaccine to about 8 million children in the United States, no cases of myocarditis have been observed.

Find out more in this article from our Vaccine Update newsletter for healthcare providers.

Watch a video featuring one of our pediatric cardiologists, Dr. Matt Elias, discussing treating patients with myocarditis.

Last updated: Jan. 20, 2022; reviewed June 21, 2022

Is it safe for my child to get the COVID-19 vaccine?

The Pfizer COVID-19 mRNA vaccine is approved for those 6 months of age and older. The Moderna COVID-19 mRNA vaccine is approved for those 6 months to 17 years of age.

At this point, millions of children and teens between 5 and 18 years of age have been safely vaccinated against COVID-19. The clinical trials in those 5 years of age and younger showed the vaccines to be safe and likely to be highly effective against severe disease. Moderna’s vaccine (6 months to 17 years of age) is one-fourth the dose of their adult vaccine and is given as two shots for healthy children in this age group. Pfizer’s vaccine (6 months to 4 years of age) is one-tenth the dose of their adult vaccine and is given as three shots for healthy children in this age group. Children 5- to 18-years of age can get the Pfizer vaccine appropriate for their age group. Specifically, doses for those 5- to 11-years of age are one-third the adult dose and is given as two doses. Those 12 years and older receive two doses of the same quantity per dose as adults.

Watch the videos in the “Perspectives on COVID-19 Vaccine for Kids” to see why others support COVID-19 vaccination of children. Individuals featured in the videos include:

  • CHOP clinicians caring for children with COVID-19
  • Adults who survived polio as children and now live with the long-term effects of the virus, called post-polio syndrome
  • Families affected by influenza, another respiratory virus that is often considered mild

Last updated: June 27, 2022

If my child is near one of the cutoff ages for different doses (5 or 12 years of age), is it better to get them vaccinated or wait?

Since COVID-19 is still circulating and it takes several weeks for a person to be considered fully immunized, it is generally recommended to start the vaccination process with the vaccine the child is currently eligible to receive even if it is a lower dose.

If your child’s birthday occurs during the period between doses, the child will be offered the higher dose for their subsequent doses.

Last updated: June 21, 2022

What side effects will my child experience from the COVID-19 vaccine?

Side effects in children were similar to what has been found in other age groups, including pain at the injection site, fatigue, headache, fever, chills, muscle pain, or joint pain.

Even though a small number of cases of myocarditis, or heart inflammation, have been identified in teens and young adults, particularly in the 4 days after receipt of the second dose of the vaccine, this side effect has not been found in younger age groups, who receive lower doses. However, it is still important to monitor younger children for this potential side effect. Chest pain, shortness of breath, or related symptoms should be reported to a healthcare provider.

Other serious side effects have not been identified, nor have long-term effects. Find additional information:

Last updated: June 21, 2022

Why do kids need the COVID-19 vaccine since they don’t get that sick if they are infected?

While children and teens may not be as likely to get severely ill from COVID-19, it can still happen and, in fact, many children have been hospitalized with COVID-19. Most often, they have not been vaccinated.

With this in mind, parents trying to decide about vaccinating their children should consider the following:

  • Conditions such as obesity, asthma, and developmental delay, as well as other pre-existing conditions, increase the chance for hospitalization.
  • As of mid-June 2022, almost 1,500 children and teens up to 17 years of age have died from COVID-19.
  • As of May 2022, more than 8,500 cases of multisystem inflammatory syndrome in children (MIS-C) have been diagnosed and 69 deaths occurred. MIS-C typically occurs 2 to 6 weeks after having COVID-19, can occur following a mild infection, tends to be more severe in adolescents and teens, and causes about 6 or 7 of every 10 individuals to be placed in intensive care. MIS-C can also affect heart function.
  • We have yet to understand the lasting effects of infection, often referred to as “long COVID” in children.
  • Finally, this age group can also transmit the infection to more vulnerable family and community members, such as those who are unable to get the vaccine.

Watch these videos, some of which feature CHOP clinicians describing caring for children with COVID-19, myocarditis, and MIS-C.

Last updated: June 21, 2022

Can the COVID-19 vaccine affect puberty or fertility in my child?

No. The rumors related to COVID-19 vaccines affecting puberty or fertility are unfounded. The mRNA vaccines are processed near the injection site and activated immune system cells travel through the lymph system to nearby lymph nodes. In this manner, they are not traveling to other parts of the body. As such, there would not be a biological reason to expect that maturation or reproductive functionality of either males or females would be negatively affected by COVID-19 vaccination now or in years to follow. Importantly, due to reports of menstrual cycle changes following vaccination, studies are currently being conducted. One early study suggested about a one-day difference in menstrual cycles; however, further data are needed to understand this finding and these reports, particularly because many factors can affect the timing of an individual’s cycle. As such, analyzing the data carefully will be important.

Watch this short video in which Dr. Paul Offit discusses COVID-19, the vaccines and infertility.

You can read more about fertility and COVID-19 vaccines in this Vaccine Update article.

Last updated: Jan. 20, 2022; reviewed: June 21, 2022

If I got a COVID-19 vaccine in another country, can I get one in the U.S.?

For individuals vaccinated in another country, they may or may not be recommended to get a COVID-19 vaccine in the U.S. based on the situation:

  • If you received the recommended number of doses and boosters of a U.S.-approved vaccine (Pfizer, Moderna, Novavax or J&J/Janssen), you do not need to do anything. If you did not receive all recommended boosters (based on your age and immune status), you should follow the U.S. recommendations.
  • If you received the recommended number of doses and boosters of a WHO-approved vaccine or all recommended doses of a mix-match scenario that included all U.S.- or WHO-approved doses, you do not need to do anything. If you did not receive all recommended boosters (based on your age and immune status), you should follow the U.S. recommendations.
  • If you received an mRNA vaccine in a country that only gives the vaccine as a single dose, you are not considered fully vaccinated in the U.S., and you should get an additional dose or doses, but you do not need to restart the series.
  • If you started, but did not finish a WHO-approved vaccine, you should get your remaining primary doses as either one of the mRNA vaccines or the protein-based vaccine (Novavax). If you require additional booster doses, they should be received in the form of one of the mRNA vaccines. However, the next dose should not be given until at least 28 days have passed since your previous dose.
  • If you got a vaccine that is not FDA- or WHO-approved, you can get the recommended number of doses of a U.S.-approved vaccine at least 28 days after your most recent dose of the non-approved vaccine. A preference has been expressed by the U.S. CDC to receive an mRNA (Pfizer or Moderna) or protein-based (Novavax) version. Booster doses can only be of the mRNA type vaccines (Pfizer or Moderna).

Last updated: July 21, 2022

What are CVST and thrombocytopenia?

Cerebral venous sinus thrombosis (CVST) is a condition that causes blood clots in large vessels that drain blood from the brain. Although it is uncommon, the condition more often affects women between 20 and 50 years of age.

Thrombocytopenia is low numbers of cells called platelets. Platelets are cells that help our blood clot. When a person has this condition, they are at risk for bleeding since their body lacks the ability to efficiently stop the bleeding.

It is very uncommon for CVST and thrombocytopenia to occur at the same time, which is what makes this diagnosis following receipt of the J&J vaccine so unusual. Likewise, the clots have not just occurred in the large vessels near the brain in some of the affected individuals. This condition was subsequently named “thrombosis with thrombocytopenia syndrome,” or TTS.

Watch this short video in which Dr. Offit discusses the differences between typical blood clots and those occasionally reported following receipt of the COVID-19 adenovirus-based vaccine.

Last updated: Jan. 24, 2022; reviewed: June 21, 2022

What is the difference between TTS and CVST?

Thrombosis with thrombocytopenia syndrome, or TTS, is the name that has been given to the condition identified in a small number of individuals after receipt of the COVID-19 J&J/Janssen or AstraZeneca vaccines. TTS is distinct from cerebral venous sinus thrombosis, or CVST, because in TTS not all clots are associated with the large vessels of the brain. Some individuals had clots in their lungs, heart, intestines, spleen, or large blood vessels in their legs. Likewise, people with TTS have a low platelet count, called thrombocytopenia, which is not typical with CVST. However, CVST was originally used to refer to these cases because they closely resembled this previously defined condition.

Watch this short video in which Dr. Offit discusses the differences between typical blood clots and those occasionally reported following receipt of the COVID-19 adenovirus-based vaccine.

For more information about TTS, watch this short animation from the Melbourne Vaccine Education Centre.

Last updated: Jan. 24, 2022; reviewed: June 21, 2022

Are some people at higher risk of having the clotting after the J&J vaccine?

In the U.S. women between 30 and 49 years of age have most often been affected by this condition compared with other groups; however, both men and women between 18 to 64 years of age have been affected.

About 1 of 500,000 vaccine recipients (with the adenovirus-based COVID-19 vaccine) will experience TTS.

Check out this infographic to see who is most often affected and how frequently this severe side effect occurs compared with others.

Last updated: Jan. 24, 2022; reviewed: June 21, 2022

Can I get the COVID-19 vaccine during my menstrual cycle?

Yes. Women do not need to schedule their COVID-19 vaccine around their menstrual cycle:

  • The immune system is not sufficiently compromised by either the COVID-19 vaccine or the menstrual cycle that scheduling them around one another would be of benefit. Indeed, delaying vaccination around a woman’s cycle may only leave her unprotected from COVID-19 for a longer time without offering any known benefit.
  • The mRNA and adenovirus vaccines are processed in immune system cells near the injection site and then those cells travel through the lymph system to nearby lymph nodes, where additional cells of the immune system are activated. As such, the vaccines would not be expected to affect the menstrual cycle. With this said, because of reported concerns, studies related to menstruation and receipt of COVID-19 are underway. An early study suggested a one-day difference in timing of menstruation; however, more data are needed since the menstrual cycle can be affected by a variety of factors. For example, hormonal changes caused by stress can affect a woman’s cycle. Women with concerns should speak with their doctor since cycles can be delayed for a variety of reasons.
  • The COVID-19 vaccine is not shed after vaccination, so being around recently vaccinated individuals would not be expected to affect someone’s cycle.

You can read more about menstruation and COVID-19 vaccines in this Vaccine Update article.

Last updated: Jan 24, 2022; reviewed: June 21, 2022

Do the COVID-19 vaccines contain live virus?

Neither the mRNA (Moderna and Pfizer) nor adenovirus (J&J/Janssen and AstraZeneca) vaccines contain live virus. Each of these contain a single gene from the virus that causes COVID-19. The gene instructs our cells to make the protein, but no other proteins from the virus are made, so whole virus particles are never present. In this manner, people who were vaccinated cannot shed, or spread, the virus to other people as a result of vaccination. If, however, the individual subsequently becomes infected, they can spread the virus during the days before and early during their infection. Of note, the amount of virus shed by vaccinated people quickly decreases, so they generally shed less virus overall compared to unvaccinated, infected individuals.

The Novavax vaccine does not contain live virus, either. It delivers the spike protein directly, rather than having our cells make the protein. As such, viral shedding does not occur following receipt of this version.

Last updated June 21, 2022

Do the COVID-19 vaccines cause viral shedding?

Viral shedding occurs when a person is infected with a virus and whole viral particles produced during the infection are transmitted in the individual’s secretions. For viruses that infect the respiratory tract, like COVID-19, these particles are often found in secretions from the nose and mouth, such as saliva or mucus.

Some people wonder whether they can shed the virus as a result of vaccination. In the case of COVID-19 mRNA and adenovirus-based vaccines approved for use in the U.S., the short answer is no. Both types of vaccines only introduce the gene for a single protein from the virus that causes COVID-19 – the spike protein. As such, whole viral particles are never produced during vaccine processing. Indeed, people are not considered to be infected when they are vaccinated because the virus does not replicate in them. Further, the vaccines are processed near the site of injection, so the spike protein produced during processing would not be found in nasal or oral secretions. As such, they cannot “shed” the single protein either. Likewise, the Novavax vaccine, which delivers the spike protein directly, cannot result in viral shedding.

However, if vaccinated people are infected, the virus will replicate at low levels in their nasal or oral cavity before the immune system stops it. In this scenario, the individual can shed the virus beginning about two days before the start of symptoms and through the first three to four days after symptoms begin.

Read more about viral shedding in this Parents PACK article, “Viral Shedding and COVID-19 — What Can and Can’t Happen."

Last updated: June 21, 2022

How do mRNA vaccines work?

People make mRNA all the time. In our cells, DNA in the nucleus is used to make mRNA, which is sent to the cytoplasm where it serves as a blueprint to make proteins. Most of the time, the proteins that are produced are needed to help our bodies function.

mRNA vaccines take advantage of this process by introducing the mRNA for an important protein from the virus that the vaccine is trying to protect against. In the case of COVID-19, the important protein is the spike protein of the SARS-CoV-2 virus. The mRNA that codes for the SARS-CoV-2 spike protein is taken up by cells called dendritic cells, which express the spike protein on the cell surface, travel to a local lymph node, and stimulate other cells of the immune system (B cells) to make antibodies. These antibodies protect us, so that if we are exposed to SARS-CoV-2 in the future, our immune system is ready and we don’t get sick.

The vaccine is processed over a 1- to 2-week period after vaccination during which time the immune response develops. However, the mRNA only directs protein production in the cell for 1 to 3 days before it breaks down. Once it breaks down, the cell stops making the spike protein.

Last updated July 29, 2021; reviewed June 21, 2022

How do adenovirus vector vaccines work?

Adenovirus vector vaccines take advantage of a class of relatively harmless viruses, called adenoviruses. Some adenoviruses cause the common cold, but others can infect people without causing illness. To use these viruses for vaccine delivery, scientists choose types of adenovirus that do not cause illness and to which most people have not been exposed. They alter the virus by removing two of the genes that enable adenovirus to replicate in people, and they replace one of those genes with the one for the SARS-CoV-2 spike protein.

Like human cells, adenoviruses contain DNA as their genetic material. So, when an adenovirus vaccine is administered, it enters cells of the immune system called dendritic cells where it releases the DNA that includes the gene for the spike protein, and the genetic material enters the nucleus of the cell. In the nucleus, the DNA is used to make messenger RNA (mRNA), which is released into the cytoplasm to serve as a blueprint for making proteins. The DNA from the viral vector, however, cannot insert into the cell’s DNA. The mRNA causes the SARS-CoV-2 protein to be produced. The dendritic cells put pieces of the SARS-CoV-2 spike protein on their surface and travel to a draining lymph node where they stimulate other cells of the immune system; specifically, B cells that make antibodies, T cells that help B cells make antibodies, and other T cells that can kill virus-infected cells. Antibodies against the spike protein will now prevent the virus from causing an infection in the future.

Find out more about adenovirus vaccines in this Vaccine Update article, “Getting Familiar with COVID-19 Adenovirus-replication-deficient Vaccines.”

Last updated: Nov. 10, 2021; reviewed June 21, 2022

How does the protein-based vaccine (Novavax) work?

The Novavax COVID-19 vaccine delivers the SARS-CoV-2 spike protein into our muscle. Once in our muscle, immune system cells that circulate throughout our body recognize the protein as foreign and attack it. Specialized immune system cells, called dendritic cells, put pieces of the protein on their surface and travel to nearby lymph nodes to activate other parts of the immune system. It takes about 1 to 2 weeks for the vaccine to be processed. The result is immunologic memory cells that are specialized to recognize the viral spike protein in the event of a future encounter with the virus.

This process takes advantage of our adaptive immune system, which responds to foreign proteins every day. To find out more about this part of our immune system, watch this animation.

Last updated: July 21, 2022

How did the vaccine companies (e.g., Pfizer and Moderna) decide which mRNA to use?

In order for a virus to reproduce and cause infection, it must get into cells and take over the cellular machinery. Because viruses attach to cells using a particular protein on their surface, in this case the SARS-CoV-2 spike protein, scientists understood that blocking that attachment would be a direct way to prevent infection. One way to block this attachment is with antibodies that bind to the surface protein. As such, when the genome was published, scientists developing the nucleic acid or protein subunit vaccines (i.e., those that only used part of the virus) chose the gene for the spike protein, anticipating that this would be the most direct route to developing an effective vaccine.

Last updated: Mar. 31, 2021; reviewed June 21, 2022

Who should NOT get the COVID-19 vaccine?

Most people are able to get COVID-19 vaccine. But, a few groups of people either should not get the vaccine or should get a particular version. Likewise, some individuals should consult with their doctor or follow special procedures.

People who should NOT get any COVID-19 vaccine:

  • Those younger than 6 months of age.
  • People currently isolating or experiencing symptoms of COVID-19; these people can get vaccinated once they are finished isolation and their primary symptoms have resolved.

People who cannot get the mRNA vaccine (Pfizer or Moderna), but may be able to get the Novavax or J&J/Janssen vaccine:

  • Anyone with a previous severe allergic reaction (i.e., one that causes anaphylaxis, any reaction that causes swelling that affects the airway (i.e., tongue, uvula, or larynx), or diffuse rash that also involves respiratory surfaces, such as Stevens-Johnson Syndrome) to a COVID-19 mRNA vaccine dose or an mRNA vaccine component.
  • Anyone with a known allergy to polyethylene glycol.

People who cannot get the adenovirus vaccine (J&J/Janssen), but may be able to get the mRNA vaccine (Pfizer or Moderna) or protein-based vaccine (Novavax):

  • Anyone with a previous severe allergic reaction (i.e., one that causes anaphylaxis, any reaction that causes swelling that affects the airway (i.e., tongue, uvula, or larynx), or diffuse rash that also involves respiratory surfaces, such as Stevens-Johnson Syndrome) to the COVID-19 adenovirus vaccine or one of its components.
  • Anyone who experienced TTS following receipt of a previous dose of adenovirus-based COVID-19 vaccine.
  • Individuals who experienced GBS within 6 weeks after receipt of an adenovirus-based vaccine or with a history of immune-mediated syndromes related to thrombosis or thrombocytopenia are not recommended to get adenovirus-based COVID-19 vaccines.
  • Anyone with a known polysorbate allergy. (These individuals cannot get the Novavax vaccine either).
  • Of note, the CDC has recommended that people get the mRNA version of COVID-19 vaccine when possible.

People who cannot get the protein-based vaccine (Novavax), but may be able to get the mRNA (Pfizer or Moderna) or adenovirus (J&J/Janssen) vaccine:

  • Anyone with a previous severe allergic reaction (i.e., one that causes anaphylaxis), any reaction that causes swelling that affects the airway (i.e., tongue, uvula, or larynx), or diffuse rash that also involves respiratory surfaces, such as Stevens-Johnson Syndrome, to a COVID-19 protein-based vaccine (Novavax) dose or one of its components.
  • Anyone with a known polysorbate allergy. (These individuals cannot get the J&J/Janssen vaccine either).

People who may get the vaccine after considering risks and benefits and/or consulting with their healthcare provider:

  • Individuals with a history of severe or immediate allergic reaction to any vaccine or injectable medication or a non-severe, immediate (within 4 hours) allergic reaction to a previous dose of COVID-19 vaccine. (These individuals should be observed for 30 minutes after receipt of the vaccine.)
  • People who have a severe or immediate allergic reaction to one of the types of vaccines and for whom the cause of the reaction is unknown (i.e., which component caused the reaction) should consult an allergist or immunologist to determine whether the individual can get the other version. If they proceed, they should be vaccinated at a location with medical facilities and staff prepared to respond to medical emergencies.
  • People who cannot get one type of COVID-19 vaccine may be able to get the other type.
  • People who are moderately or severely ill (regardless of whether they have a fever) may delay vaccination until they feel better.
  • People with a history of MIS-C should delay vaccination until at least 90 days after diagnosis and they experience a return of normal cardiac function and considered clinical recovered. Likewise, the risk for exposure should be high. Those with a history of MIS-A should be clinically recovered, including return to normal cardiac function.
  • People who experienced myocarditis or pericarditis after receipt of mRNA or Novavax vaccine are typically advised not to get additional doses of any COVID-19 vaccine due to limited data about safety. In some instances, individuals and their healthcare providers may decide to proceed with an additional dose based on the risk-benefit assessment. Note: This does not apply to people with history of myocarditis or pericarditis unrelated to COVID-19 vaccination, nor does it apply to people with a history of heart disease.

People who should follow special procedures

  • Someone with a history of severe or immediate allergic reaction (requiring medical intervention) to anything other than a vaccine or injectable medication can get the vaccine, but they should remain at the vaccination location for medical observation for 30 minutes after receipt of the vaccine.
  • Pregnant women who develop a fever after vaccination should take acetaminophen. (See more in the pregnancy-related questions lower on this page.)
  • People treated with convalescent plasma should not receive measles- or varicella-containing vaccines until at least 7 months after receipt of the plasma.
  • People with a known COVID-19 exposure should wait until their quarantine is over before getting vaccinated. Unique situations may warrant vaccinating during this period, such as living in a situation with repeated exposures (e.g., living in a group setting, such as a nursing home, correctional facility, or homeless shelter) or having limited ability to be vaccinated after quarantine has ended.

Last updated July 21, 2022

Where can I get the vaccine?

COVID-19 vaccines are generally widely available. As such, we recommend checking for vaccine at your provider’s office, local pharmacies, healthcare facilities, mass vaccination sites or mobile clinics. For children younger than 5 years of age, we recommend contacting your child’s healthcare provider or checking with clinics or pharmacies before going for vaccination as some may have certain age requirements for administering vaccines.

You can find your state’s information about COVID-19 vaccine distribution using this information prepared by our colleagues at Vaccinate Your Family.

Last updated: Nov. 10, 2021; reviewed June 21, 2022

What are the side effects of the COVID-19 vaccine?

Common side effects from the mRNA, adenovirus and protein-based vaccines are caused as part of the immune response to each.

mRNA vaccines: Older children and adults 

The most common side effects from the mRNA vaccines (Pfizer and Moderna) are:

  • Fatigue
  • Headache
  • Muscle aches

Side effects occurred during the first week after vaccination but were most likely one or two days after receipt of the vaccine. During clinical trials, side effects were more frequent following the second dose and more likely to be experienced by younger, rather than older, adults. Although most people will not have significant side effects, some people may wish to schedule their vaccination, so that they will not need to call out of work the next day if they don’t feel well.

A small number of people who get the mRNA vaccine experience mild, short-lived inflammation of the heart, called myocarditis. About 1 of every 50,000 mRNA vaccine recipients experience this condition, but it is most likely in adults 29 years and younger and more often occurs in males. This condition tends to occur within 4 days of receipt of the second dose, but can occur after any dose and up to several days after vaccination. Recently vaccinated individuals who experience chest pain or shortness of breath should seek medical care. This condition tends to resolve within 2-3 weeks and does not cause long-term heart damage. Importantly, COVID-19 infections can also cause myocarditis, and this tends to occur more frequently after infection compared with vaccination. (See “My teen is a student-athlete and already had COVID-19, so does he need the COVID-19 vaccine? We are worried about myocarditis.” on this page for more detailed information.)

mRNA vaccines: Children younger than 5 years of age

Young children who received either the Pfizer or Moderna mRNA vaccine commonly experienced:

  • Pain, tenderness, and swelling near the injection site
  • Fever
  • Irritability
  • Decreased appetite
  • Fatigue

Older children in this age group, who are better able to communicate what they are feeling, sometimes also experienced headaches, chills, achiness or joint pain, and nausea or vomiting. These effects were somewhat more likely after receipt of the Moderna vaccine, which is a higher dose, but occurred infrequently overall.

Myocarditis was not detected in either clinical trial; however, because COVID-19 mRNA vaccines are a rare cause of myocarditis in older adolescents and young adults, it is possible that it could be observed in younger children. Experience with these vaccines in older children and adults suggest that the likelihood of myocarditis is significantly lower following vaccination compared with infection. Also, the doses given to this age group are even lower than those given to older children and adults. However, parents and care providers should still monitor their children in the days following vaccination and contact healthcare providers or seek emergency care should concerns arise.

Protein-based vaccine: Adults

The most common side effects from the protein-based vaccine (Novavax) are:

  • Injection site pain and less often redness or swelling
  • Headache
  • Fatigue
  • Muscle aches

A small number of cases of myocarditis have occurred in individuals who received this vaccine; however, additional data are necessary to determine the level of risk. Recently vaccinated individuals who have heart-related symptoms should seek medical care.

Adenovirus-based vaccine: Adults

The most common side effects from the adenovirus vaccine (Johnson & Johnson/Janssen) are:

  • Injection site pain and less often redness or swelling
  • Headache
  • Fatigue
  • Muscle aches
  • Fever

Side effects occurred during the first seven to eight days after vaccination but were most likely to occur one or two days after receipt of the vaccine. Side effects were more often experienced by younger, rather than older vaccine recipients.

Two rare, but potentially dangerous conditions, have been identified following receipt of the adenovirus-based vaccines, such as the J&J/Janssen version:

  • Thrombosis with thrombocytopenia syndrome, or TTS, occurs in about 1-2 of every 1 million vaccine recipients and develops up to 3 weeks after getting vaccinated. Individuals between 18 and 64 years of age, both female and male, who got the J&J/Janssen vaccine have experienced this condition; however, women between the ages of 30 and 49 years of age are at the greatest risk. Anyone who got the J&J/Janssen vaccine less than 3 weeks ago should seek medical care if they develop severe headache, shortness of breath, severe abdominal pain, unexplained leg pain, easy bruising, or small red spots on the skin. Anyone seeking medical care with one or more of these symptoms should mention their recent receipt of the vaccine, so healthcare providers can order the appropriate diagnostic tests and treatments.
  • Guillain-Barré syndrome, or GBS, occurs in about 1 of every 100,000 vaccine recipients, most often during the first 3 weeks after getting vaccinated. The condition has most often been identified in males between 50 and 64 years of age, but it can occur in females and those 65 years and older on occasion. While rare, most cases have required hospitalization and at least one person has died. Anyone who recently received an adenovirus-based COVID-19 vaccine and experiences muscle weakness or paralysis should seek medical treatment and inform the healthcare provider of the recent vaccination. It should also be noted that COVID-19 infection has been associated with GBS; so, natural infection with SARS-CoV-2 also appears to be a rare cause of GBS. Find out more about GBS in this Parents PACK article, “Guillain-Barré Syndrome (GBS) & Vaccines: The Risks and Recommendations.”

Illustration of who is most at risk for these side effects Check out this infographic [PDF, 157KB] to see a visual representation of this information.

Last updated: July 21, 2022

Can I take medicine for the side effects after I get the vaccine?

The CDC has indicated that you can take anti-fever or anti-inflammatory medications if necessary following COVID-19 vaccination, but it is important to know that doing so could diminish the level of immunity that develops. This is true anytime you take these types of medications, whether following vaccination or to treat illness. Generally speaking, the “symptoms” people experience following vaccination or during illness, such as fever, redness at the injection site, or fatigue, are caused by your immune system response. For example, fever is your body turning up its “thermostat” to make the immune system more efficient and the pathogen less efficient. For these reasons, if you are not very uncomfortable, it is better not to take these medications.

Some wonder how long they should wait after vaccination before taking these types of medicines, so their immune response is not affected. As a rule of thumb, the immune response following receipt of the mRNA vaccine develops over a week or two after vaccination and for the adenovirus vaccine, over the course of about four weeks, but the greatest chance of affecting your immune response would be in the first few days after receipt of the vaccine. Indeed, in the adenovirus vaccine studies, about 1 in 4 vaccine recipients took fever-reducing medication (antipyretics), and most people were still protected from severe disease and all were protected against hospitalization.

Find out more in this Parents PACK article, "Medications and COVID-19 Vaccines: What You Should Know."

Last updated: Mar. 1, 2021; reviewed June 22, 2022

If I don’t have side effects, does that mean the vaccine did not work?

Many people will get the vaccine and not experience side effects. This does not mean that the vaccine did not work for them. In the clinical trials side effects occurred at varying rates, for example only about 1 to 20 of every 100 people who received the mRNA vaccine had a fever, but we know that the mRNA vaccine worked for more than 90 of every 100 people.

Last updated: Mar. 1, 2021; reviewed June 22, 2022

What are the expected long-term side effects of the vaccination for COVID-19?

  • Most negative effects occur within 6 weeks of receiving a vaccine, which is why the FDA asked the companies to provide 8 weeks of safety data after the last dose.
  • mRNA vaccines: The mRNA in the vaccine breaks down quickly because our cells need a way to stop mRNA from making too many proteins or too much of a single protein. But, even if for some reason our cells did not breakdown the vaccine mRNA, the mRNA stops making the protein within about a week, regardless of the body’s immune response to the protein.

    Read more about COVID-19 mRNA vaccines in this Parents PACK article, “Long-term Side Effects of COVID-19 Vaccine? What We Know.”

    Watch a short video of Dr. Paul Offit explaining why COVID-19 vaccines would not be expected to cause long-term side effects.
     
  • Adenovirus-based vaccines: Although the DNA from adenovirus-based vaccines does not break down as quickly as mRNA, the DNA cannot alter our DNA because a gene for the enzyme, integrase, is not present. These vaccines are processed within about 4 weeks, so they would not be expected to cause any long-term effects either.
  • Protein-based vaccines: The protein is processed within a few days. 

Last updated: July 21, 2022

Should I stop taking my daily dose of aspirin before getting the COVID-19 vaccine?

If your daily dose of aspirin was prescribed by your physician following a stroke or heart attack, we recommend speaking to that doctor about whether to stop taking your medication for a day or two prior to vaccination. If, however, your daily dose of aspirin is because you have risk factors for a stroke or heart attack (such as high blood pressure or high levels of “bad” cholesterol) but have never had a stroke or heart attack, you should talk to your doctor about discontinuing the aspirin not only prior to your COVID-19 vaccine, but all together. The data show that while daily aspirin helps prevent second strokes or heart attacks, it does not help prevent first occurrences, even in people who are at increased risk. Our director, Dr. Paul Offit, carefully reviewed the data related to this topic for his book, Overkill: When Modern Medicine Goes Too Far.

Find out more in this Parents PACK article, "Medications and COVID-19 Vaccines: What You Should Know."

Last updated: Jan. 24, 2022; reviewed: June 22, 2022

What should I do if I took pain medicine before getting the COVID-19 vaccine?

While your initial immune response may have been lower, you will likely still have developed some immunity. Even if your immune response is somewhat lower overall, you are likely to develop sufficient levels of immunity to reduce your chance for infection. In addition, even if you were infected, you would be likely to experience disease that is less severe and of shorter duration.

Last updated: Mar. 1, 2021; reviewed June 22, 2022

What is the difference between the first and second dose of the COVID-19 mRNA vaccine?

In the United States, the ingredients in the vial for dose 1 and dose 2 of the same brand are exactly the same. When people talk about dose 1 doses and dose 2 doses, they are just talking about vaccine supply. If you arrive for dose 1 and the person behind you is getting dose 2, they can come out of the same vial.

One vaccine used in some other countries, Sputnik V, has different components in dose 1 and dose 2. Both are adenovirus vector vaccines, but dose 1 uses adenovirus 26 (Ad26) and dose 2 uses adenovirus 5 (Ad5).

Third doses (booster doses) of the Moderna vaccine are half the dose of previous doses; however, Pfizer vaccine third doses (booster doses) are the same as doses 1 and 2. Second doses of J&J/Janssen are the same as first doses of that brand.

The Pfizer vaccine given to children 5 to 11 years of age is one-third the dose given to those 12 years and older; however, a child’s dose 1 and dose 2 is the same. The children’s doses are delivered in vials with orange caps to distinguish them from the purple or gray caps on vials with adult doses of the Pfizer vaccine.

The Pfizer vaccine given to children between 6 months and 4 years of age is one-tenth the Pfizer dose given to adults; however, the three doses are the same. These doses are delivered in vials with maroon caps to distinguish them from the other versions of the Pfizer COVID-19 vaccine.

The Moderna vaccine given to children between 6 months and 17 years of age is one-fourth the Moderna dose given to adults; however, the two doses given in this age group are the same.

Last updated: June 27, 2022

Can I get the second dose of COVID-19 mRNA vaccine in my other arm?

Yes. It is okay to get the second dose in the other arm as the immunity generated by the first dose will be circulating in your body watching for a potential exposure.

Indeed, individuals who experience a delayed reaction at the injection site (a rash that develops a few days to a couple of weeks after receipt of the vaccine) are recommended to get the second dose in the opposite arm.

Last updated: Mar. 1, 2021; reviewed June 22, 2022

Can additional doses of the COVID-19 vaccine be from a different company?

The CDC recommends that people get the same version for all primary doses (first two doses of Pfizer, Moderna or Novavax and first dose of J&J/Janssen) whenever possible.

People getting an additional dose of mRNA vaccine for an immune-compromising condition should also seek the same version as originally received when possible.

Booster doses should be mRNA version vaccines. 

Last updated: July 21, 2022

How long do I need to wait if I had or need to get a non-COVID-19 vaccine?

In most cases, individuals do not need to delay receipt of COVID-19 vaccine and other vaccines; however, if given during the same appointment, the vaccines should be administered in different locations (different arms or separated by at least one inch on the same arm).

The one exception is that people who get an orthopox vaccine (monkeypox/smallpox), particularly teen and young adult males, should consider waiting for 4 weeks before getting a COVID-19 mRNA or protein-based vaccine due to known or potential risks of myocarditis related to individual orthopox and COVID-19 mRNA and protein-based vaccines. However, if the individual is at risk for monkeypox due to an outbreak or exposure and recently had a COVID-19 mRNA or protein-based vaccine, they should not delay their orthopox vaccination given that they would be trading a real risk for a theoretical risk by delaying.

Watch this short video in which Dr. Hank Bernstein explains the benefits of receiving routine vaccines at the same time as the COVID-19 vaccine.

Last updated: July 21, 2022

Are young children susceptible to COVID-19, especially if a parent tests positive?

If a parent tests positive, they should try to isolate from other members of the household.  Others in the home, including any children, should follow guidance based on their immunization status. If not vaccinated, individuals should quarantine and be monitored for symptoms, as per CDC recommendations for exposure. If fully vaccinated or had a positive COVID-19 viral test within the last 90 days, individuals do not need to quarantine, but they should monitor for symptoms, per the CDC guidelines.

See the CDC guidance, Quarantine and Isolation, for the latest recommendations, including how to calculate quarantine.

Last updated: Jan. 24, 2022; reviewed: June 22, 2022

What is multisystem inflammatory syndrome (MIS-C or MIS-A)?

Multisystem inflammatory syndrome can occur in children (MIS-C) or adults (MIS-A). Development of symptoms typically occurs about 4 to 6 weeks after SARS-CoV-2 infection and can occur even in those who did not experience symptoms of COVID-19. Often multiple organs and body systems are involved, including effects on the gastrointestinal tract, heart, kidneys, skin, lungs, and eyes. Individuals with unexplained rash, vomiting or diarrhea, shortness of breath or chest pain or palpitations should seek medical care. Some people with MIS-C or MIS-A will require admission to intensive care and a small number may require mechanical ventilation.

Find out more about MIS-C and long COVID-19 in this video with one of CHOP’s infectious diseases pediatricians.

Watch this short video in which Dr. Offit discusses MIS-C, MIS-A, and long COVID.

Last updated: Jan. 24, 2022; reviewed: June 22, 2022

What is long COVID?

Long COVID, also known as post-COVID conditions or long-term COVID, is characterized by long-lasting symptoms related to previous SARS-CoV-2 infection. Symptoms can last for weeks or months after viral clearance and resolution of the initial infection. Examples of the types of symptoms that affected individuals report include fatigue, difficulty thinking or concentrating (“brain fog”), headache, change in or loss of taste or smell, dizziness, heart palpitations, chest pain, shortness of breath, cough, joint or muscle pain, anxiety, depression, sleep problems, feelings like “pins and needles,” diarrhea or stomach pain, rash, changes in menstrual cycle, or fever. Symptoms sometimes appear or worsen after physical or mental activity. People, particularly those who experienced severe COVID-19 infections, may also develop new chronic conditions, such as diabetes, heart conditions or neurological conditions.

The reasons for or susceptibility to these long-lasting effects remain uncertain but are being studied. Early data suggest that some people may be at greater risk of developing post-COVID conditions, including those who experienced more severe illness (e.g., hospitalized or required intensive care), developed multisystem inflammatory syndrome (MIS-C or MIS-A), had pre-existing health conditions or were unvaccinated.

Watch this short video in which Dr. Offit discusses MIS-C, MIS-A, and long COVID.

Find out more about MIS-C and long COVID-19 in this video with one of CHOP’s infectious diseases pediatricians.

Last updated: June 22, 2022

Does a vaccinated person present a risk to an unvaccinated person?

Vaccinated people do not shed virus as a result of vaccination. Neither the COVID-19 mRNA nor the adenovirus vaccines are composed of live viruses, so there is no infectious virus to spread from a vaccinated person to someone else. The same is true of the newer vaccine, Novavax, which is composed of the single spike protein.

But a vaccinated person can still be infected and potentially spread the virus to others. If they do not have symptoms, they may spread the virus without even knowing they are infected. While vaccinated individuals who become infected can be a source of viral spread, they do not appear to spread as much virus as unvaccinated individuals who become infected because their immune response is able to respond to the infection more quickly – shortening the length of infection and, therefore, the amount of virus produced.

Read more, “Vaccinated or Unvaccinated: What You Should Know.”

Last updated: June 22, 2022

What ingredients are in the COVID-19 mRNA vaccine?

The mRNA vaccines include:

  • mRNA – This mRNA is for the spike protein of SARS-CoV-2, the virus that causes COVID-19.
  • Lipids - These are molecules that are not able to dissolve in water. They protect the mRNA, so that it does not break down before it gets into our cells. These can be thought of as little “bubbles of fat,” which surround the mRNA like a protective wall. There are four different lipids in the Pfizer vaccine and three in the Moderna vaccine. One of the lipids in both vaccines is cholesterol. The lipids are the most likely components of the vaccine to cause allergic reactions.
  • Salts and amines - The Pfizer vaccine contains four salts. One is table salt. The salts are used to keep the pH of the vaccine similar to that found in the body, so that the vaccine does not damage cells when it is administered. The Moderna vaccine also contains four chemicals to balance the pH, but two are in a class of organic compounds known as “amines” and two are acetic acid and its salt form, sodium acetate. Acetic acid is the main component of vinegar (other than water).
  • Sugar – This ingredient is literally the same as that which you put in your coffee or on your cereal. It is used in both of the vaccines to help keep the “bubbles of fat” from sticking to each other or to the sides of the vaccine vial.

These are the only ingredients in the mRNA vaccines.

NOT in the COVID-19 mRNA vaccines:

Watch this short video in which Dr. Paul Offit talks about the ingredients of COVID-19 mRNA vaccines.

Last updated Feb. 19, 2021; reviewed June 22, 2022

What ingredients are in the COVID-19 adenovirus-based vaccine?

The adenovirus vaccine includes:

  • Adenovirus type 26 (Ad26) containing SARS-CoV-2 spike protein gene and altered so that it cannot replicate
  • Stabilizers – Salts, alcohols, polysorbate 80, and hydrochloric acid
  • Manufacturing by-products – amino acids

Because the adenovirus-based COVID-19 vaccine is grown in fetal cells. Although the product is highly purified, remnants of these cells may remain in the final product. 

NOT in the COVID-19 adenovirus vaccines:

Last updated: Jan. 24, 2022; reviewed: June 22, 2022

What ingredients are in the COVID-19 protein-based vaccine (Novavax)?

The protein-based vaccine includes:

  • SARS-CoV-2 spike protein
  • An adjuvant derived from the soap bark tree (Quillaja saponaria), called Matrix-M
  • Stabilizers – Salts (including table salt), polysorbate 80, and hydrochloric acid

NOT in the COVID-19 protein-based vaccine:

Last updated: June 22, 2022

Do COVID-19 vaccines contain antibiotics?

No. Neither the mRNA vaccines (Pfizer and Moderna), adenovirus vaccine (Johnson & Johnson/Janssen), nor the protein-based COVID-19 vaccine (Novavax) contain antibiotics.

Watch this short video in which Dr. Hank Bernstein discusses which ingredients are and are not in the COVID-19 mRNA vaccines.

Last updated: June 22, 2022

Can mRNA vaccines change the DNA of a person?

Since mRNA is active only in a cell’s cytoplasm and DNA is located in the nucleus, mRNA vaccines do not operate in the same cellular compartment that DNA is located.

Further, mRNA is quite unstable and remains in the cell cytoplasm for only a limited time (See “What stops the body from continuing to produce the COVID-19 spike protein after getting an mRNA vaccine?” below.) mRNA never enters the nucleus where the DNA is located so it can’t alter DNA.

Watch this short video in which Dr. Paul Offit explains why it’s not possible for mRNA vaccines to alter a person’s DNA.

Last updated Dec. 15, 2020; reviewed June 22, 2022

Can adenovirus-based vaccines change the DNA of a person?

Adenovirus-based vaccines contain DNA, which enters the nucleus of cells after vaccination, but the virus cannot replicate and the vaccine does not include a necessary enzyme, called integrase. Therefore, the vaccine cannot change a person’s DNA.

Last updated: Mar. 1, 2021; reviewed June 22, 2022

What stops the body from continuing to produce the COVID-19 spike protein after getting a COVID-19 mRNA or adenovirus- based vaccine?

Both the mRNA and adenovirus vaccines result in production of spike protein that results from mRNA blueprints. Because our cells are continuously producing proteins, they need a way to ensure that too many proteins do not accumulate in the cell. So, generally speaking, mRNA is always broken down fairly quickly. Even if for some reason our cells did not breakdown the vaccine mRNA, the mRNA stops making the protein within about a week, regardless of the body’s immune response to the protein. Once the mRNA is broken down, the blueprint is gone, so the cell can no longer continue to make spike proteins.

Likewise, while the adenovirus-based vaccine delivers DNA and the DNA lasts longer than mRNA, studies have shown that adenovirus-based DNA does not last longer than a few weeks.

Watch this short video in which Dr. Hank Bernstein explains how the mRNA from the COVID-19 vaccine is broken down and removed from the body.

Last updated Apr. 23, 2021; reviewed June 22, 2022

Will the spike protein from current vaccines cause an issue if there are future variants?

This question has two aspects – longevity of the spike protein and effects of current immune responses to future variants. While related, these are not cumulative issues, meaning they involve separate considerations:

  • Longevity of the spike protein - The spike protein does not remain in the body for an extended time, nor does it travel around the body. The only thing that remains after the vaccine is processed are antibodies and memory immune cells that will recognize the virus if we are exposed in the future. The antibodies and memory cells will or will not recognize the variant spike protein. If they do, great – we will have some protection. If they don’t, it will be just like an antibody to some unrelated pathogen (like flu or measles), it will have no effect.
  • Effects of current immune responses to future variants - As the virus evolves, it changes, so we might find ourselves dealing with different versions of the virus in the future. Current variants have not changed significantly enough that our antibodies have stopped being protective against severe disease. However, the variants have changed enough that protection against any infection (i.e., non-severe infection) is lower. For this reason, some of the companies are testing newer versions of COVID-19 vaccine in an effort to improve our immunity. With this said, it is important to realize that because the current vaccines remain effective at preventing severe disease, hospitalization and death, unvaccinated people can still benefit from receiving currently available versions.

Last updated: June 22, 2022

Is it safe to get the COVID-19 vaccine if I have COVID-19?

The CDC recommends waiting until your symptoms go away and you are no longer isolating. If you happen to be infected, but don’t know because you have not yet developed symptoms or you have an infection without symptoms, the vaccine is not likely to be harmful. It would increase your body’s immune response against the virus.

Last updated Jan. 19, 2021; reviewed June 22, 2022

Can I drink alcohol after getting the COVID-19 vaccine?

Alcohol suppresses the immune system, so it would be advisable not to drink alcoholic beverages for about 2 weeks after getting vaccinated.

Last updated: Dec. 31, 2020; reviewed June 22, 2022

Is it okay to donate blood after getting the COVID-19 vaccine?

Giving blood after getting the COVID-19 vaccine will not diminish the resulting immune response, which mostly builds in the lymph nodes near the injection site. Likewise, the American Red Cross (ARC) does not require a delay following vaccination with the vaccines currently approved for use in the U.S.; however, individuals must know which brand of vaccine they received and show the immunization card if possible. More details about blood donation are available on the ARC website.

Last updated: Mar. 18, 2021; reviewed June 22, 2022

Are COVID-19 vaccines made in fetal cells?

The mRNA vaccines (those by Pfizer and Moderna) and the protein-based vaccine (Novavax) do not contain fetal cells.

But, the adenovirus-based vaccines, like Johnson & Johnson/Janssen’s, use cells originally isolated from fetal tissue (often referred to as fetal cells). These fetal cells are used to grow the vaccine virus.

To replicate, a virus needs to take over a cell’s machinery (See this animation); however, the adenoviruses used in these vaccines have been altered, making them unable to complete the replication process. So, to make the vaccine, these altered viruses need to infect cells that have been changed in a way that allows the defective virus to reproduce. The special cells for this process were isolated decades ago from one of two terminated fetuses and later adapted for the adenovirus reproduction process. Neither of these are used to produce any existing vaccines grown in fetal cells:

  • HEK-293 — This is a kidney cell line that was isolated from a terminated fetus in 1972.
  • PER.C6 — This is a retinal cell line that was isolated from a terminated fetus in 1985.

These two cell lines have been maintained in the laboratory, and no additional fetuses are needed to produce adenovirus-vector vaccines.

In this short video, Dr. Paul Offit addresses fetal cells and COVID-19 vaccines.

You can find out more about the adenovirus-based vaccines and fetal cells in this Vaccine Update article.

Last updated June 22, 2022

How many doses of a COVID-19 vaccine will be needed?

Over time, as we have learned more about the virus that causes COVID-19 (called SARS-CoV-2) and witnessed its ability to change, the recommendations about the number of vaccine doses for individuals have changed. As with any developing area of science, the recommendations and terminology may change more in the future. However, at the moment, here is a summary to help you sort through the recommendations:

Primary series

Primary doses of a vaccine are those doses needed to induce a robust immune response the first time someone is introduced to a pathogen. A person is not considered immunized against a particular pathogen until they have completed all primary doses. Currently in the U.S., primary dose recommendations are slightly different for healthy people and those with a condition that compromises their immune system. Likewise, variations exist across vaccines.

Most individuals

  • Pfizer – Three primary doses for those 6 months to 4 years of age and two primary doses for those 5 years of age and older.
  • Moderna – Two primary doses for those 6 months and older.
  • Novavax – Two primary doses for those 18 years and older.
  • J&J/Janssen – One primary dose for those 18 years of age and older, although the U.S. CDC has expressed a preference for individuals to use other types of COVID-19 vaccine when possible due to rare, but real, severe side effects.

People with immune-compromising conditions

  • Pfizer – Three primary doses for all age groups.
  • Moderna – Three primary doses for all age groups.
  • Novavax – Two primary doses for those 18 years and older.
  • J&J/Janssen – One primary dose of J&J/Janssen followed 4 weeks later by one dose of an mRNA-based version (booster). This vaccine is only for those 18 years and older.

Booster doses

Booster doses of a vaccine are those doses needed to “remind” the immune system about a pathogen. Booster doses of COVID-19 vaccines have been demonstrated to increase the level of antibodies circulating in the blood, thereby decreasing the chance for any infection (e.g., mild infection). Currently, in the U.S., booster dose recommendations differ slightly by age and immune status. Likewise, variations exist across vaccines.

Most individuals

  • Pfizer – One booster dose at least 5 months after the last primary dose for those 5 years of age and older. Individuals 50 years and older are recommended to get a second booster dose at least 4 months after the previous booster dose. This means those 5 to 49 years of age are recommended to get a total of three doses and those 50 and older, a total of four doses. No boosters are recommended for those 6 months to 4 years of age at this time.
  • Moderna – One booster dose at least 5 months after the last primary dose for those 18 years of age and older. Individuals 50 years and older are recommended to get a second booster at least 4 months after the previous booster dose. This means that those 18 to 49 years of age are recommended to get a total of three doses and those 50 and older, a total of four doses. Children 17 years and younger are not recommended to get booster doses at this time.
  • Novavax – No booster doses are recommended for recipients of this vaccine at this time. This vaccine is only approved for those 18 years of age and older and cannot be used for booster doses in those who received other types of COVID-19 vaccine.
  • J&J/Janssen – If someone 18 years or older received two doses of the J&J/Janssen vaccine (one primary and one booster), they can get an additional (booster) dose of an mRNA-based version. Those 50 years and older are recommended to get a second booster (third or fourth dose total, depending on their number of J&J/Janssen doses).

People with immune-compromising conditions

  • Pfizer – One booster dose at least 3 months after the last primary dose for those 5 to 11 years of age and two booster doses for those 12 years and older (3 months between last primary and first booster; 4 months between first and second booster). This means that those 5 to 11 years of age with an immune-compromising condition are recommended to get a total of four doses and those 12 and older in this situation, a total of five doses. Children younger than 5 years of age with immune-compromising conditions are not currently recommended to receive any boosters.
  • Moderna – Two booster doses for those 18 years and older with immune-compromising conditions for a total of five recommended doses for this group. Booster doses should be given at intervals of at least 3 months between the last primary and first booster doses and at least 4 months between first and second booster doses. Children who are 17 years of age and younger with immune-compromising conditions are not currently recommended to receive any boosters.
  • Novavax – No booster doses are recommended for recipients of this vaccine at this time. This vaccine is only approved for those 18 years of age and older and cannot be used for booster doses in those who received other types of COVID-19 vaccine.
  • J&J/Janssen – Two booster doses for those 18 years and older with immune-compromising conditions (2 months after dose two and at least 4 months between doses three and four). Additional doses are recommended to be mRNA-based whenever possible. For most individuals in this group, they will receive a total of four doses, unless they happened to receive two doses of J&J/Janssen vaccine, in which case they may have had five doses in total.

Last updated: July 21, 2022

How long will vaccine immunity last?

We are still learning how long immunity lasts after infection or vaccination. The latest information shows that:

  • Following infection people are not likely to be re-infected within 90 days of infection. However, more work is needed to understand how long immunity lasts following infection, particularly because the virus that causes COVID-19 continues to change. Immunity against mild disease doesn’t last as long as protection against severe disease.
  • Following vaccination, most people were protected against severe disease caused by the delta variant for at least 9 months and likely much longer. Protection against mild illness caused by omicron and omicron variants is less robust. As such, additional booster doses have been recommended for certain high-risk groups and companies are working to develop updated versions that offer better protection against the newer variants.

Last updated: June 23, 2022

If you had the virus, do you still need to get the vaccine?

People who had COVID-19 are recommended to get the vaccine after they have recovered. Some studies have indicated two benefits:

  • Vaccination more consistently produces protective immune responses than infection.
  • Vaccination provides a wider breadth of protection based on the types of memory responses produced.

In addition, studies have suggested that infection followed by vaccination provides better protection than either vaccination or infection alone.

Last updated: Jan. 24, 2022; reviewed: June 23, 2022

Could taking two different vaccines boost the effectiveness?

Currently, the Centers for Disease Control and Prevention (CDC) recommends getting all primary doses of the same mRNA or protein-based vaccine unless the supply does not allow for doing so.

The CDC recommends getting mRNA or protein-based vaccines when possible unless an individual requires or prefers J&J/Janssen for a particular reason or if the supply limits one’s choice.

Booster doses are recommended to be mRNA-based versions. The protein-based vaccine (Novavax) is currently not approved for booster doses.

Last updated: July 21, 2022

Is a coronavirus vaccine necessary?

SARS-CoV-2 infections can be a minor hindrance or lead to severe disease or even death. Likewise, some people, including children, experience lingering symptoms, called “long COVID,” which is yet to be understood. While hygiene measures such as social distancing, handwashing, and wearing masks offer some help, the best way to stop this virus is to generate SARS-CoV-2-specific immunity. No virus has ever eliminated itself by inducing natural immunity in a large percentage of the population. Only herd immunity induced by vaccination can eliminate viruses, as has now been shown for smallpox and two of the three different types of poliovirus.

For more information, watch this short video of Dr. Paul Offit addressing “Why does it matter if I don’t get the COVID-19 vaccine?”

Last updated: June 23, 2022

How long before a coronavirus vaccine takes effect?

The Pfizer mRNA vaccine requires two or three doses for those greater than 6 months of age, depending on age and immune status. Protection against severe disease is greatest about 2 weeks after the last primary dose.

The Moderna mRNA vaccine requires two or three doses for the primary series in those less than 17 years of age, depending on immune status. While children will have some immunity after each dose, protection will be most likely about one week after receipt of the last primary dose. Most children and adults greater than 17 years of age are recommended to get at least one additional dose of Moderna’s vaccine depending on their age and immune status. Find out more in the answer to “How many doses of a COVID-19 vaccine will be needed?”

The protein-based vaccine (Novavax) requires two doses. Immunity will be most robust about two weeks after the second dose.

The adenovirus vaccine (Johnson & Johnson/Janssen) requires one dose. While people will have some immunity about two weeks after being vaccinated, protection will be more robust about one month after receipt of the vaccine. Likewise, individuals are recommended to get a second dose at least 8 weeks after the first dose to further bolster their immunity. The second dose is preferred to be an mRNA-based version.

Last updated: July 21, 2022

Do the variants affect vaccine effectiveness?

Current variants circulating in the U.S. are being monitored for their ability to spread, cause more severe disease, and evade vaccines and treatments. Current vaccines will protect many against severe disease and death; however, booster doses have been recommended to bolster immunity while scientists work on newer versions  that can better protect against currently circulating variants. Because the original mRNA vaccines remain effective against severe disease and death for most people, vaccination of unvaccinated individuals is still recommended.

Last updated: June 23, 2022

Can pregnant women get the COVID-19 vaccine?

Pregnant women were not included in the early COVID-19 vaccine studies, but some participants were either pregnant and did not know it or became pregnant during the course of the study. Likewise, tens of thousands of pregnant women have been safely immunized since the COVID-19 mRNA vaccines became available.

With data from thousands of these women now in hand, no concerns have been identified and the vaccine works. While pregnant women and their babies will continue to be monitored, the CDC recently changed its statement about COVID-19 vaccines for pregnant women to more clearly recommend these vaccines for pregnant women.

Two factors, in addition to the vaccine data, were important for informing vaccine recommendations for pregnant women:

  • First, some pregnant women are at high risk for COVID-19 because of their jobs, such as healthcare workers, or existing health conditions.
  • Second, pregnant women are more likely to be hospitalized and be admitted to the intensive care unit with COVID-19 than women of the same age who were infected but weren’t pregnant.

All pregnant women should keep these two important points in mind:

  1. Pregnant women who get the COVID-19 vaccine should take acetaminophen if they develop a fever after vaccination, as fever during pregnancy can negatively affect a developing baby. Taking acetaminophen during pregnancy has been found to be safe.
  2. Likewise, regardless of vaccination status, pregnant women should practice recommended public health measures, particularly because of their increased risk if infected with COVID-19.

In this short video, Dr. Hank Bernstein discusses COVID-19 vaccination during pregnancy.

You can read more about pregnancy and COVID-19 vaccines in this Vaccine Update article.

Drs. Paul Offit and Ripudaman Minhas discuss vaccines, pregnancy, development and autism in this video.

Last updated: Jan. 25, 2022; reviewed: June 23, 2022

Can I get the COVID-19 vaccine if I am breastfeeding?

Yes. Although women who are breastfeeding were not included in the clinical trials, data have indicated that COVID-19 is not transmitted through breast milk, so it is not expected that vaccination would cause a concern either. On the other hand, some women who are breastfeeding will be at higher risk for exposure, so they could benefit from receiving the vaccine.

In addition, women do not need to delay breastfeeding for any period of time before or after they have been vaccinated.

Babies may benefit from antibodies or immune cells introduced through breast milk after the mother is vaccinated. This is called passive immunity.

Both the Academy of Breastfeeding Medicine and the American College of Obstetricians and Gynecologists support this approach.

In this short video, Dr. Hank Bernstein discusses COVID-19 vaccination when breastfeeding.

You can read more about breastfeeding and COVID-19 vaccines in this Vaccine Update article.

Drs. Paul Offit and Amna Husain discuss vaccines and breastfeeding in this video.

Last updated: Jan. 25, 2022; reviewed: June 23, 2022

Can I get the COVID-19 vaccine if I am trying to get pregnant?

Yes, women who are trying to get pregnant can get the COVID-19 vaccine. Likewise, if a woman finds out she is pregnant after starting vaccination but before receiving all recommended doses, she can still continue with vaccination, and it is important to do so since pregnant women are at higher risk of being hospitalized and having pre-term births if infected with COVID-19 during pregnancy.

Last updated: June 23, 2022

Should I delay getting pregnant if I got the COVID-19 vaccine?

No, you do not need to delay pregnancy. The COVID-19 vaccines do not present a cause for concern related to pregnancy.

Last updated: Jan. 25, 2022; reviewed: June 23, 2022

Why was I told to wait a month after getting the COVID-19 vaccine before getting a mammogram?

Some people experience swelling of the lymph nodes under their vaccinated arm after getting the COVID-19 mRNA vaccine. Because this could be mistakenly identified as spread of breast cancer to lymph nodes, delaying the mammogram can prevent the chance of this happening.

Last updated: Jan. 25, 2022; reviewed: June 23, 2022

Why was I asked if I recently received the COVID-19 vaccine on the questionnaire for my MRI?

People occasionally experience swelling of the lymph nodes near the vaccine injection site, which could interfere with interpreting the results of the MRI depending on what location is being imaged.

Last updated: Jan. 25, 2022; reviewed: June 23, 2022

Is it necessary to wait to get blood work done after getting the COVID-19 vaccine?

Generally speaking, it would be recommended to wait about a week after getting the mRNA vaccine and a few weeks after getting the adenovirus-based vaccine before getting bloodwork. Delays are not likely to be needed after receipt of the protein-based vaccine. However, it would be better to inquire with the healthcare provider who ordered the bloodwork as they have the benefit of knowing the reason for the bloodwork, the type of tests ordered, and the patient’s medical history. As such, they will be in the best position to offer this guidance for each individual situation.

Last updated: July 21, 2022

If I have an autoimmune or immune-compromising condition, can I be vaccinated?

People with immune-compromising conditions may get the COVID-19 vaccine as long as they are not in one of the following categories:

  • Severe allergy to a vaccine component (i.e., one that causes anaphylaxis or requires medical intervention)
  • History of severe allergy to any vaccine or injectable medication

However, it is recommended that individuals with compromised immune systems discuss their personal risks and benefits with a healthcare provider to determine whether to receive the vaccine or if they may need additional doses.

Knowing the potential for a lower immune response, if someone with an immune-compromising condition decides to get vaccinated, it will be important to get all recommended doses, depending on their condition (See “How many doses of a COVID-19 vaccine will be needed?” for more details). They may also choose to continue practicing other public health measures during periods of high virus circulation.

Last updated: June 23, 2022

Can I get the COVID-19 vaccine if I had Guillain-Barré Syndrome (GBS)?

People with a history of Guillain-Barré Syndrome (GBS) can get the COVID-19 vaccine, as long as they do not have another condition that puts them among the people recommended against vaccination. Since a small number of cases of GBS have been identified following receipt of the adenovirus-based COVID-19 vaccine (J&J/Janssen), a preference has been expressed for use of the mRNA- or protein-based vaccines. GBS cases following receipt of the adenovirus-based vaccine have been rare (about 1 of 100,000 people), but if an individual developed GBS within 6 weeks of receiving it, they should only get future doses of a different type of vaccine. Individuals who had GBS in the past, have a “precaution” against the adenovirus-based COVID-19 vaccine, meaning they may be able to get it if they and their healthcare provider determine that the benefits outweigh the potential risks; however, since mRNA and protein-based vaccines are more widely available, preferred, and have not been linked to GBS, most individuals and their healthcare providers will likely settle on one of these versions for vaccination.

A note about GBS and influenza vaccines

Some people wonder if they can get the COVID-19 vaccine if they developed GBS following receipt of an influenza vaccine. Since COVID-19 and influenza (flu) vaccines are made differently, people with this history would not be expected to have an issue with COVID-19 vaccine. As such, they are still recommended to get COVID-19 vaccine.

Finally, many people are incorrectly told that if they had GBS, they cannot get a flu vaccine. However, most people with a history of GBS can get the flu vaccine. Only people who were diagnosed with GBS less than 6 weeks after receipt of influenza vaccine are considered to have a “precaution” for receipt of influenza vaccine, meaning that the patient and the healthcare provider should discuss the relative risks and benefits associated with getting the influenza vaccine. In fact, studies have shown that influenza disease presents a greater risk of GBS than influenza vaccination. Find out more:

Last updated: July 21, 2022

Can I still get vaccinated if I have a cold?

People with mild cold-like symptoms are not prevented from getting the vaccine. However, if they are not feeling well, their symptoms just started, or their symptoms are getting worse, they may want to delay vaccination until they feel better; otherwise, they might not be able to tell effects of illness from those of the vaccine. If they are uncertain, they should speak to their doctor, who has the benefit of their medical history and will be in the best position to help them weigh the potential pros and cons.

Last updated: Mar. 1, 2021; reviewed June 23, 2022

If I had dermal fillers, can I get the COVID-19 vaccine?

The receipt of dermal fillers does not prevent someone from getting the COVID-19 vaccine. While a few people with dermal fillers have experienced swelling in the area of the fillers following receipt of the mRNA vaccine (most often, but not exclusively, Moderna), these events have been extremely rare and have responded to treatment. Likewise, at least one case has also been identified following COVID-19 infection.

You can read more from the The Aesthetic Society, the American Society of Plastic Surgeons, and the American Society for Dermatologic Surgery.

Last updated: Oct. 13, 2021; reviewed June 23, 2022

If I am taking anticoagulants (blood thinners), can I get the COVID-19 vaccine?

Patients on blood thinners can get the COVID-19 vaccine. However, because the vaccine is given intramuscularly, the risk for bleeding is slightly greater for these individuals. As such, they should tell the healthcare provider administering the vaccine about their use of an anticoagulant. The vaccine itself does not increase the risk for this group of patients.

Find out more in this Parents PACK article, "Medications and COVID-19 Vaccines: What You Should Know."

Last updated: Sept 28, 2021; reviewed June 23, 2022

If I am currently taking antibiotics, can I get the COVID-19 vaccine?

As long as you are not still sick from your recent infection, you can get the COVID-19 vaccine even if you are taking an antibiotic. But, if you are still having symptoms, you should wait until you are feeling better, so that it is easier to tell if any new symptoms are from your infection or the vaccination.

Find out more in this Parents PACK article, "Medications and COVID-19 Vaccines: What You Should Know."

Last updated: Sept. 28, 2021; reviewed June 23, 2022

If I am taking antivirals, can I get the COVID-19 vaccine?

You do not need to stop taking antiviral medication before vaccination. Because the COVID-19 vaccines being used in the U.S. do not rely on viral replication, antivirals should not affect development of the immune response. However, if you are still experiencing symptoms of the infection for which the antivirals were prescribed, you should wait until you are feeling better before getting the vaccine. This will allow you to distinguish symptoms from your infection with side effects from the vaccine.

Find out more in this Parents PACK article, "Medications and COVID-19 Vaccines: What You Should Know."

Last updated: June 23, 2022

If I am taking biologics, can I get the COVID-19 vaccine?

Taking biologics, like Humira, is not a reason to forgo COVID-19 vaccination as per CDC guidelines. However, patients taking these types of medication may wish to consult with their doctor to discuss the potential risks and benefits of getting the COVID-19 vaccine, given that these types of medications are often prescribed for individuals with immune-compromising conditions. As a result, there may be other considerations related to the potential risks and benefits of vaccination.

For general information about vaccines and biologics, check out this printable Q&A sheet.

Find out more in this Parents PACK article, "Medications and COVID-19 Vaccines: What You Should Know."

Last updated: Jan. 25, 2021; reviewed June 23, 2022

If I need a dental procedure, can I get the COVID-19 vaccine, or should I delay my procedure?

People can have dental procedures after receipt of the COVID-19 vaccine. Vaccine-induced immunity should not be affected by nitrous oxide or antibiotics that might be prescribed after the procedure.

Last updated: Jan. 25, 2021; reviewed June 23, 2022

How long should I wait to get the COVID-19 vaccine after getting a steroid injection or vice versa?

You should speak with your doctor to determine whether the quantity of steroids that you are receiving is suppressing your immune system. If so, you should hold off on receiving vaccines until the effect of the steroids has worn off.

Find out more in this Parents PACK article, "Medications and COVID-19 Vaccines: What You Should Know."

Last updated: Jan. 25, 2021; reviewed June 23, 2022

Does the COVID-19 vaccine cross the blood-brain barrier?

It would not be expected that the COVID-19 vaccines would cross the blood-brain barrier (BBB) for a few reasons.

mRNA vaccines:

  • Most of the protein that is made is bound to cells - The vaccine is injected into muscle, where dendritic cells in the area use the mRNA to make the COVID-19 spike protein. These dendritic cells, after making the spike protein, put the protein (not the mRNA) on the cell surface, travel to the nearest lymph node, and stimulate other cells of the immune system to make an immune response against the protein. This process is typical of our adaptive immune system, which you can find out more about in this animation, or you can watch this animation that describes how the mRNA vaccine is processed.
  • Even if the protein left the cell whole (which it doesn’t), it is too large to cross the BBB.

Adenovirus vaccine:

Protein-based vaccines (e.g., Novavax) would not be expected to cross the BBB either as the proteins are too large.

Last updated: June 23, 2022

Does the COVID-19 vaccine cause antibody-dependent enhancement (ADE)?

Antibody-dependent enhancement (ADE) occurs when the antibodies from a previous infection (or vaccination) help the virus gain access to cells rather than blocking access to cells. Getting an infection after vaccination does NOT provide evidence of ADE. These are two distinct immunologic phenomena.

ADE has not been identified as a concern related to SARS-CoV-2 infection or following COVID-19 vaccination. In fact, a body of evidence has suggested that ADE is not a concern:

  • First, most people have been infected with other coronaviruses in their lifetime, and ADE has not been identified as a result of these infections.
  • Second, in human studies, people previously infected with coronavirus were infected with different types of coronavirus, and they did not experience enhanced disease.
  • Third, experimental animals vaccinated against SARS-CoV-2 did not develop enhanced disease when challenged, or infected, with the virus.
  • Fourth, when people with COVID-19 received plasma containing SARS-CoV-2 antibodies, they did not experience enhanced disease.
  • Finally, millions of people have been vaccinated against COVID-19, and some of them have subsequently been infected with SARS-CoV-2, or one of its variants, and none of them have shown evidence of ADE.

Scientists will continue to monitor the SARS-CoV-2 variants; however, it would not be expected that ADE will become an issue with the rise of new variants, as it has not been with the many types of coronaviruses and the existing SARS-CoV-2 variants to date.

Watch a short video in which Dr. Paul Offit explains why COVID-19 vaccines are unlikely to cause ADE.

Last updated: Jan. 25, 2022; reviewed: June 23, 2022

Does the COVID-19 vaccine cause fertility issues?

Infertility has not been found to be an issue in women or men infected with or vaccinated against COVID-19.

Unfortunately, misinformation about fertility-related issues has been circulating online. These concerns take a few forms:

  1. Compromised fertility in the vaccine recipient – Original concerns related to a placental protein, called syncytin-1. This protein is associated with the placenta during pregnancy. Online claims promoted a paper suggesting that a small number of similar amino acids in the spike protein and the placental protein would cause vaccine-induced antibodies to react against syncytin-1. Since human proteins are made using the same 20 amino acid building blocks, many proteins have short sections that are similar to one another. However, most of our antibodies do not cross-react with other proteins because a variety of other factors come into play. The most important of which is antibody specificity to the three-dimensional version of its target. As such, while a theoretical paper like the one previously mentioned can generate an interesting hypothesis, the idea requires clinical confirmation, which never materialized for this idea that unfortunately spread quickly and, quite frankly, unnecessarily scared people.
  2. Some concerns related to males, and whether the vaccines could decrease sperm count. While fever can cause a temporary decrease in sperm count, there is no biologically plausible reason to expect that the vaccines would cause any long-term effect on sperm count.
  3. Compromised fertility in individuals near someone who recently received COVID-19 vaccine – This misperception conflates two concepts: effects on fertility and viral shedding. As mentioned above, the vaccines do not affect fertility in the vaccinated person, so there would not be a reason to expect that they would affect someone else’s fertility. Second, it assumes that recently vaccinated individuals shed virus or spike protein. Neither of these occur. While these vaccines cause the body to generate spike protein, they do not cause production of whole virus particles, nor do parts of the vaccine migrate to the nasal cavity. As such, a recently vaccinated person does not shed any part of the virus and cannot, therefore, spread vaccine-related components to another person.

Watch this short video in which Dr. Paul Offit discusses COVID-19, the vaccines and infertility.

You can read more about fertility and COVID-19 vaccines in this Vaccine Update article.

This Parents PACK article about vaccination of children 5 to 11 years of age also addresses fertility-related concerns.

Last updated: Jan. 25, 2022; reviewed: June 23, 2022

Will I be able to get the coronavirus vaccine at the same time as other vaccines?

The CDC recommendations allow people to get COVID-19 vaccines at the same time as most other vaccines. This decision was made due to experience with more than one vaccine given close in time with COVID-19 vaccines during emergency situations and with more understanding of the effects of the COVID-19 vaccines, suggesting a low likelihood of interference. However, studies will continue to monitor responses during these situations to ensure that unexpected events do not occur. The CDC change also considered the increased susceptibility of individuals who missed routinely recommended vaccines during the pandemic. If an individual is uncomfortable getting both vaccines at once and can conveniently return for a second visit, the vaccines can be separated by two weeks, but if the individual can’t return in a timely manner, it is acceptable to give both vaccines at the same visit but in separate locations.

One notable exception is a recommendation to delay COVID-19 mRNA- or protein-based vaccination (Pfizer, Moderna, or Novavax) for 4 weeks after receiving an orthopox vaccine (monkeypox/smallpox), due to risks of myocarditis associated with both types (COVID-19 and orthopox) of vaccine. This is particularly relevant for teen and young adult males. However, if the individual was recently vaccinated against COVID-19 and then is recommended to get the orthopox vaccine due to an outbreak or known exposure, they should not delay vaccination.

Watch this short video in which Dr. Hank Bernstein explains the benefits of receiving routine vaccines at the same time as the COVID-19 vaccine.

Last updated: July 21, 2022

Is there any hope that a vaccine will help people with lingering after effects from coronavirus?

The lingering effects of COVID-19 are concerning, and we still have much to learn about them. A vaccine will help from the point of view that if it decreases infections, fewer people will experience illness and, therefore, fewer people will experience long-term effects. But, it is not likely that a vaccine will address these effects in someone who was already infected.

Last updated: Dec. 15, 2020; reviewed June 23, 2022

Does the COVID-19 vaccine contain blood products?

The COVID-19 vaccines available in the U.S. do not contain any blood products, including red blood cells, white blood cells or platelets. 

Watch this short video in which Dr. Offit talks about the ingredients used in the COVID-19 mRNA vaccines.

Last updated: Mar. 1, 2021; reviewed June 23 2022

How can I know about COVID-19 disease in my community or where I am traveling?

During the height of the COVID-19 pandemic, several tools were developed to help public health officials, governments, businesses, and individuals make informed decisions. These tools typically used county-level data to provide guidance. Some of these tools are no longer in operation; however, you can still assess county-level risk using the “COVID-19 event risk assessment planning tool,” developed by teams at Georgia Institute of Technology and Applied Bioinformatics Laboratory. This tool shows the percent chance that at least one person will be COVID-19 positive in gatherings of different sizes. The calculations are based on results of data from COVID-19 antibody blood tests.

Last updated: June 23, 2022

Was the genome of the virus subject to peer review or FDA/CDC oversight?

The viral genome is not a product; it represents scientific knowledge, so organizations like the FDA or CDC would not have “oversight” over the information. However, this question gets at the heart of how science is done. Scientists by their nature are skeptics, and the scientific process is designed to challenge rather than accept results. In this manner, several points offer reassurance that the genomic sequence was vetted for accuracy:

  • The scientists who reported the genome isolated samples from several patients to examine the genome. Said another way, their data were not based on a single person’s infection. They had to confirm for themselves and for the quality of their research that what they found was accurate. They could not assume that the same virus was causing infections without actually gathering evidence of such.
  • Once they completed their study, they had to share it with colleagues, who would critically review it and maybe even ask for more experiments or clarifications before they could publish a paper sharing their results with the world. Peer-review is critical to the scientific process, which is why you may have heard about data that were not yet peer-reviewed during the pandemic. For scientists, that means that the work has not yet been vetted.
  • Several other labs also isolated samples from patients and reproduced the process. Their papers were also peer reviewed before publication. Reproducibility is a second critical component of the scientific process. Even if the genomic information passed peer review and was published, if other labs did not find the same thing, the information would be called into question.

In this manner, the pillars of scientific integrity — peer review and reproducibility — can offer everyone reassurance that the genomic sequence was accurate— not to mention the fact that vaccines based on the information have been effective at preventing infection.

Last update: Mar. 31, 2021; reviewed June 23, 2022

I heard that steps were skipped to make a vaccine more quickly. Is that true?

While COVID-19 vaccines were developed more quickly than ever before, it was imperative that speed did not decrease safety.

In this case, the timeline was shortened without sacrificing quality by:

  • Skipping phase I or combining phase I with phase II trials — Since phase I studies include a small number of people and evaluate whether the candidate vaccine causes an immune response and is safe, scientists could look at data from a group of people as phase II was progressing to make these evaluations.
  • Manufacturing “at risk” — While completing the large phase III clinical trials, manufacturers began producing the vaccine, so that if it was shown to be safe and effective, they would have large numbers of doses ready. The reason this is not typically the approach is because if the vaccine does not work, the manufacturer will have spent a significant amount of money to produce something that needs to be thrown away.
  • Support efforts — While waiting for a vaccine to be ready, many other aspects of vaccine delivery were prepared, including:
    • Developing plans for how to distribute the first, limited quantities available
    • Ensuring adequate supplies for distributing and administering vaccine, like vaccine vials, syringes and other equipment needed to vaccinate
    • Establishing mechanisms for distribution to large subsets of the population, especially in countries in which mechanisms may not currently be in place. For example, many countries do not have standard programs for vaccinating older adults. So, planning how to reach those people, without unintentionally exposing them to a crowd in which the virus may be spread, was something that could be planned during vaccine development.

Watch this video in which Dr. Paul Offit explains the COVID-19 vaccine trials.

Last updated: Dec. 15, 2020; reviewed June 23, 2022

Do COVID-19 vaccines contain a microchip?

COVID-19 vaccines do not contain microchips. This idea is based on a false narrative and misinformation campaign waged online. You can find out more about where this idea came from on snopes.com.

Last updated: Dec. 15, 2020; reviewed June 23, 2022

If my baby has had some of her vaccines, is she protected from COVID-19? We are anxious for her to meet family members.

A baby’s vaccines should not be anticipated to protect the baby from COVID-19. So, when trying to decide when it may be safe for family to meet the baby during COVID, parents should not rely on other vaccinations as a source of protection. While some have hypothesized that other vaccines may be protective, this protection would not be specific to COVID-19.

If the baby is at least 6 months of age, she can receive the COVID-19 vaccine; however, she should not be considered immune until at least 2 weeks after receipt of her last dose (3 doses for the Pfizer vaccine and 2 doses for the Moderna vaccine).

Last updated: Dec. 15, 2020; reviewed June 23, 2022

COVID-19 video resources

This section of the page will house video resources and interviews related to COVID-19.

Vaccine Makers Project videos and animations
The Vaccine Makers Project (VMP) is the classroom program of the Vaccine Education Center (VEC). VMP resources include a variety of science-based animations that show not only how COVID-19 vaccines work, but also how viruses take over our cells and how our immune systems work.

Myths and misinformation surrounding COVID-19 vaccines
Vaccine Education Center (VEC) Current Issues in Vaccines webinar, Sept. 28, 2021 (Please note that you will need to register to gain immediate access to the recording. If you are a healthcare professional seeking continuing education credits for viewing this event, please review the continuing education information on this page.)

Talking about Vaccines with Dr. Paul Offit: COVID-19
This VEC playlist features several short videos in which Dr. Offit addresses common questions about COVID-19.

Talking about Vaccines with Dr. Hank Bernstein: COVID-19
This playlist features a series of short videos in which Dr. Hank Bernstein answers common questions about COVID-19 vaccines.

My COVID-19 Vaccine Experience
These short videos share personal experiences and decision-making related to receipt of the COVID-19 vaccine.

Perspectives on COVID-19 Vaccine for Kids
These short videos feature personal experiences from clinicians caring for kids with COVID-19; families affected by flu, another virus sometimes perceived as insignificant in kids; and survivors of polio, another virus that causes long-term effects.

Vaccinate Your Family’s COVID-19 Vaccine Updates: Zoom Series Featuring Top Officials from FDA and CDC, series hosted by Vaccinate Your Family

Last updated: June 23, 2022

Reviewed by Paul A. Offit, MD on July 21, 2022

Materials in this section are updated as new information and vaccines become available. The Vaccine Education Center staff regularly reviews materials for accuracy.

You should not consider the information in this site to be specific, professional medical advice for your personal health or for your family's personal health. You should not use it to replace any relationship with a physician or other qualified healthcare professional. For medical concerns, including decisions about vaccinations, medications and other treatments, you should always consult your physician or, in serious cases, seek immediate assistance from emergency personnel.