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. 

Can't find what you're looking for?

  1. Check the “Archived COVID-19 Questions” page.
  2. Ask your COVID-19 vaccine questions here.

You can also find information related to COVID-19 in these additional resources:

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].

Last updated: Jan. 18, 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. However, they indicate that it is okay to get the COVID-19 vaccine or booster shortly after recovering from the disease as long as the patient was not treated with antibody-based treatments (convalescent plasma or monoclonal antibodies):

  • Someone who received antibody-based treatment after exposure (called prophylaxis), should wait 30 days before getting vaccinated.
  • Someone who received antibody-based treatment during illness, should wait 90 days before getting vaccinated.
  • If you are not sure, talk to the healthcare providers who treated you or contact your primary care physician for help determining whether you fall into this category.

Due to limited supplies of vaccine in some countries and the experience that people who recently had COVID-19 rarely get re-infected in the months immediately after recovery, some areas may be delaying vaccination of recently recovered individuals. As such, we recommend talking with your healthcare provider or health officials to see what the recommendations are in your area.

Last updated Jan. 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

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

J&J/Janssen adenovirus vector vaccine

People who received the J&J/Janssen vaccine should get a second dose of vaccine separated by at least 8 weeks, regardless of their health status. They are not currently recommended to get a third dose of the J&J/Janssen vaccine.

Pfizer or Moderna mRNA vaccine

A third dose of COVID-19 mRNA 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.

How the third dose is implemented will be affected by which of these reasons are the cause for the additional dose.

The Centers for Disease Control and Prevention (CDC) has recommended a third dose of mRNA vaccine for the following groups of people:

  • Additional primary dose: Immune-compromised individuals, 18 and older (Moderna or Pfizer); those 5 to 17 years of age (Pfizer). Those 5 to 11 years old should get the child dose, and those 12 and older should get the adult dose (even if they originally received the child dose).
  • Booster dose: People 12 years of age and older, even if they were younger than 12 years of age when originally vaccinated.

Those getting an additional primary dose should get the same type and dose of vaccine they received initially when possible.

Those getting a booster dose can get any type of vaccine. Importantly, booster doses of Moderna should be half the quantity of the primary dose. Pfizer booster doses are the same quantity as the primary dose (purple cap for those 12 and older).

Those younger than 12 years of age should only get two doses of lower-dose Pfizer vaccine (orange cap) separated by at least 21 days.

Immune-compromised individuals (additional primary dose)

Individuals 12 years of age and older in this category should get the same brand of mRNA vaccine that their original vaccine was whenever possible. Those 5 to 11 years of age are only eligible for Pfizer vaccine (orange cap). The second and third doses should be separated by at least 28 days. The third dose in this scenario should be the same quantity as the first two doses.

People in this category 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 in this category who should work with their healthcare provider to determine their need for a third dose 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.

People 12 years of age and older

Individuals who received the mRNA vaccine should get a third dose, separated by at least 5 months from the second dose. Booster doses of Moderna should be half doses. It should be noted that, to date, booster dosing has not been shown to enhance protection against serious disease in otherwise healthy young people.

Last updated: Jan. 20, 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 Jan. 20, 2022

When will COVID-19 vaccines be available for children younger than 5 years of age?

COVID-19 vaccine trials are in progress for children younger than 5 years of age.

Find out more about COVID-19 clinical trials in children in this Parents PACK article, including how the trials are being done, what will be learned and more.

Last updated: Jan. 20, 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

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 16 years of age and older, and Moderna’s, for those 18 years and older.

Last updated: Feb. 1, 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

Is it safe for my adolescent or teen to get the COVID-19 vaccine?

The Pfizer COVID-19 mRNA vaccine is approved for those 5 years of age and older. Other COVID-19 vaccines are still being tested in those younger than 18 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.

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: Jan. 20, 2022

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

Side effects in children 5 to 11 years of age 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. However, side effects tended to be less frequent than in other age groups.

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 the younger age group. 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: Jan. 20, 2022

If a person has allergic reactions to a food or medication, can they get the vaccine?

People with severe allergies to a COVID-19 vaccine ingredient (see list here) or a previous dose of COVID-19 vaccine should not get that type of COVID-19 vaccine (mRNA or adenovirus-based). They may be able to get the alternative type after consultation with an allergist or immunologist. Individuals with a known allergy to polysorbate should not get the COVID-19 vaccine made by Johnson & Johnson/Janssen.

People with immediate allergic reactions to an injectable medication can most often get the COVID-19 vaccine; however, they should remain at the site where they were vaccinated for 30 minutes of observation, instead of the 15 minutes that the general public is recommended to wait. Anyone with this type of allergy who has questions or concerns should discuss the situation with their healthcare provider to assess the potential risks and benefits of receiving the COVID-19 vaccine. 

People who have had an anaphylactic reaction to anything else (medications, foods, bees, etc.) are allowed to get the COVID-19 vaccine, but should remain at the site where the injection was given for 30 minutes, instead of the 15 minutes that the general population are recommended to wait.

The CDC published information about allergic reactions that caused anaphylaxis after almost 2 million doses of the Pfizer vaccine were given. They estimate that about 30% of the population has allergies. However, only 21 anaphylactic allergic reactions occurred in those 2 million vaccine recipients. Of these 21 people, 17 of 21 had previously identified allergies, but 4 of 21 had no previously identified allergies at all. Of those who had allergies, no significant pattern emerged, suggesting that there is not a causal association between allergies (or specific allergies) and an anaphylactic reaction to the vaccine. Further, since millions more doses have been administered, this rate of allergic reaction has not continued, suggesting that the likelihood of having an allergic reaction following receipt of the COVID-19 vaccine is not likely to differ from background rates.

If a person with history of allergies continues to have concerns about whether or not it is safe to get the COVID-19 vaccine, they should contact their primary care provider or allergist, who has the benefit of their complete medical history and will, therefore, be in the best position to discuss any potential risks and benefits for that individual.

Last updated: May 27, 2021; reviewed: Jan. 20, 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-Jan. 2022, more than 700 children and teens up to 17 years of age have died from COVID-19.
  • As of early Jan. 2022, more than 6,400 cases of multisystem inflammatory syndrome in children (MIS-C) have been diagnosed and 55 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: Jan. 20, 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

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 of a U.S.-approved vaccine (2 doses Pfizer, 2 doses Moderna, or 1 dose of J&J/Janssen), you are considered fully vaccinated. However, you should follow the U.S. recommendations regarding an additional dose (see “Do I need another dose of COVID-19 vaccine?”).
  • If you received the recommended number of doses of a WHO-approved vaccine or all recommended doses of a mix-match scenario that included at least one non-U.S. approved dose, you are considered fully vaccinated, but you may need an additional dose based on your health status or to fulfill the booster recommendation.
  • 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, but you do not need to restart the series.
  • If you started, but did not finish a WHO-approved vaccine, you can a dose of the Pfizer vaccine as long as at least 28 days have passed since your previous dose. After this dose, you will be considered fully vaccinated, but may need an additional dose based on your health status or to fulfill the booster recommendation.
  • 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 version. This group is not currently recommended to get a third dose.

Last updated: Jan. 20, 2022

What should I do if I had the J&J vaccine?

People who had a single dose of the J&J/Janssen vaccine are recommended to get a second dose at least 8 weeks after the first dose.

Related to side effects

If you had the J&J/Janssen vaccine within the last 3 weeks, although the risk is low, you should monitor yourself for unusual symptoms, including severe headache, severe abdominal pain, unexplained leg pain, or shortness of breath, which may result from TTS, or muscle weakness or paralysis, which may result from GBS. If you develop unusual symptoms, you should seek medical attention and be certain to tell the healthcare provider the date you received the J&J/Janssen vaccine. For TTS, the physician can very quickly determine whether your problem is related to the vaccine by performing a simple complete blood count. If the platelet count is extremely low, the symptoms might be related to the vaccine. We would also recommend registering for v-safe, the CDC’s vaccine monitoring system if you have not done so already.

If you had the J&J/Janssen vaccine more than 3 weeks ago, you are extremely unlikely to experience either thrombosis with thrombocytopenia syndrome (TTS) or Guillain-Barré syndrome (GBS).

Last updated: Nov. 10, 2021; reviewed: Jan. 10, 2022

Should I stop using my birth control if I got the J&J vaccine?

It is not necessary to stop taking birth control pills. Individuals affected by thrombotic thrombocytopenic syndrome (TTS), which is an unusual combination of low platelet count (thrombocytopenia) and clotting (thrombosis) did not share common medical histories, such as use of birth control pills; therefore, stopping usage would not change your risk for TTS.

Last updated: Apr. 23, 2021; reviewed: Jan. 20, 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

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, and may still be used to refer to the condition by some individuals, because the original cases 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

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

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

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.

Last updated Jan. 24, 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, 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 mRNA and adenovirus-based vaccines approved for use in the U.S., the short answer is no. Both of these types of vaccines only introduce 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.

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: Jan. 24, 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 Jan. 24, 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 Jan. 24, 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 Jan. 24, 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 5 years 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 resolved as long as they did not receive antibody-based medications after exposure or as part of their treatment. In which case, they will need to delay vaccination for 30-90 days, depending on their situation. They should talk to their doctor.

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

  • Anyone with a previous severe or immediate allergic reaction (i.e., one that causes anaphylaxis or requires medical intervention) 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):

  • Anyone with a previous severe or immediate allergic reaction (i.e., one that causes anaphylaxis or requires medical intervention) to the COVID-19 adenovirus vaccine or one of its components
  • Anyone with a known polysorbate allergy
  • Those 5-18 years of age can get the Pfizer mRNA vaccine, but not other versions (as long as they do not have other contraindications that prevent receipt of the vaccine).
  • Of note, the CDC has recommended that people get the mRNA version of COVID-19 vaccine when possible.

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 (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 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 who recently had COVID-19 and were treated with antibody-based therapies (e.g., monoclonal antibodies or convalescent plasma) should wait until 90 days after treatment to be vaccinated against COVID-19.
  • People who received an antibody-based therapy following COVID-19 exposure (but not infection) should wait 30 days after treatment to be vaccinated.
  • People treated with convalescent plasma should not receive measles- or varicella-containing vaccines until at least 7 months after receipt of the plasma.
  • Children (C) or adults (A) diagnosed with multisystem inflammatory syndrome (MIS-C or MIS-A) should seek guidance from their treatment team regarding vaccination and if getting vaccinated, delay vaccination until they recover and at least 90 days have passed from their diagnosis of this condition.
  • People with a known COVID-19 exposure should wait until their quarantine is over before getting vaccinated (unless they live in a group setting, such as a nursing home, correctional facility, or homeless shelter, in which case they can be vaccinated during the quarantine period).

Last updated Jan. 24, 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 5 to 11 years of age, we recommend contacting facilities in advance to ensure that they are vaccinating that age group.

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 Jan. 24, 2022

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

Side effects from both the mRNA and adenovirus vaccines are caused as part of the immune response to the vaccine.

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. 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.)

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: Jan. 24, 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, or fatigue, are caused by your immune system responding. 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 Jan. 24, 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 Jan. 24, 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 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.

Last updated: Jan. 24, 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

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 Jan. 24, 2022

What if I can’t get the second dose 21 (Pfizer) or 28 (Moderna) days after the first dose?

The Centers for Disease Control and Prevention (CDC) allows for a 4-day grace period when assessing on-time receipt. This means the following ranges of days are considered “on-time” for receipt of the second dose:

  • Pfizer vaccine: 17 to 25 days after the first dose
  • Moderna vaccine: 24 to 32 days after the first dose

People should try to get the second dose during this period or as soon after as possible. However, if your second dose is given later than this, you do not need to restart the vaccine. It is important to note that during the clinical trials the first dose did not protect as many people as were protected after the second dose, so if you are exposed to SARS-CoV-2 during the delay, you may or may not have enough immunity to prevent you from experiencing symptoms. The timing of your third dose would be based on when you got the second dose.

Last updated: Jan. 24, 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 of the Moderna vaccine are half the dose of previous doses; however, Pfizer vaccine third doses are the same as doses 1 and 2. Second doses of J&J/Janssen are the same as first doses of that brand.

Finally, of note, 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.

Last updated: Jan. 24, 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 Jan. 24, 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 or Moderna 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.

People getting boosters can change their version, but if no compelling reason exists to change and the previous version is available, they may try to get the same type. The one exception is that individuals who received the J&J/Janssen version should consider switching to an mRNA version, per CDC guidance. Also of note, people getting a booster dose of Moderna should only receive a half dose.

Last updated: Jan. 24, 2022

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

The Centers for Disease Control and Prevention (CDC) has updated their recommendations, so that individuals do not need to delay between receipt of COVID-19 vaccine and other vaccines.

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: May 13, 2021; reviewed Jan. 24, 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

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

What is long COVID?

Long COVID, also known as COVID syndrome or long-term COVID, is a condition 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, loss of taste or smell, dizziness, heart palpitations, chest pain, shortness of breath, cough, joint or muscle pain, anxiety, depression, or fever. Symptoms sometimes appear or worsen after physical or mental activity. The reasons for or susceptibility to these long-lasting effects remain uncertain but are being studied.

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: Jan. 24, 2022

Does a vaccinated person present a risk to unvaccinated family members in the same house?

Vaccinated people do not shed virus as a result of vaccination. Neither the 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.

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 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.

Given that young children and possibly some family members and friends remain unvaccinated, those who have been vaccinated should continue to follow public health guidance when they are out in the community to decrease spread of the virus. Even when a whole family is vaccinated, continuing to practice these measures remains important for two reasons:

  1. The vaccine will not work for everyone, so someone in the home who has been vaccinated may still be susceptible.
  2. People outside of the family’s “bubble,” like co-workers, extended family members, neighbors, and others they come into contact with, may not have been vaccinated (or may be in the group for whom the vaccine does not work).

This approach will be important until we can get control over the spread of virus. Once enough people have become immune, we will all be able to move away from these public health measures.

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

Last updated: Jan. 24, 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:

The CDC has the list of specific lipids and salts posted on its website.

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

Last updated Feb. 19, 2021; reviewed Jan. 24, 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:

  • Animal Products
  • Antibiotics
  • Blood products
  • Egg Proteins
  • Gluten
  • Microchips
  • Pork products
  • Preservatives, like thimerosal
  • Soy

Last updated: Jan. 24, 2022

Do COVID-19 vaccines contain antibiotics?

No. Neither the mRNA vaccines (Pfizer and Moderna) nor the adenovirus vaccine (Johnson & Johnson/Janssen) 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: Mar. 1, 2021; reviewed Jan. 24, 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 Jan. 24, 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 Jan. 24, 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 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 Jan. 24, 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 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, so for now, we do not need different vaccines. If, however, one (or more) of these variants changes enough that the vaccine-induced immunity (or disease-induced immunity) is no longer protective against severe disease and death, we will need to make new COVID-19 vaccines that protect against the new version of the virus. As described above, in this scenario the existing immunologic memory (antibodies or memory cells) will no longer be effective, but it will not be problematic either. A new vaccine would induce new immunity and the process would begin anew.

Last updated: Jan. 24, 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 Jan. 24, 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 Jan. 24, 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 Jan. 24, 2022

Are COVID-19 vaccines made in fetal cells?

The mRNA vaccines (those by Pfizer and Moderna) 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, so that they cannot replicate. So, to make virus to use as the vaccine, these altered viruses need to infect cells that have been altered in a way to allow 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.

Last updated Mar. 1, 2021; reviewed Jan. 24, 2022

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

The mRNA vaccines require two doses, and most individuals are recommended to get  a third dose (see “Do I need another dose of the COVID-19 vaccine?” for more details). For the Pfizer vaccine, the two doses should be separated by 21 days. For Moderna’s vaccine, the two doses should be separated by 28 days. The timing and quantity of the third dose depends on the reason for it (See aforementioned question and answer.).

The adenovirus vaccine (Johnson & Johnson/Janssen) is recommended as two doses separated by at least 8 weeks.

Last updated: Jan. 24, 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, they are working to learn more about immunity following infection. While some people have been re-infected after recovering from COVID-19, the number of people who have experienced this is small compared with the total number of people who have been infected.
  • Following vaccination, people are immune for at least 6 months and likely much longer. Based on the elements of the immune response activated after vaccination with either the mRNA or adenovirus vaccines, it is likely that immunity against severe disease will be long-lived. However, decreasing antibody levels in the bloodstream have prompted a recommendation for most people to get a third dose (See more details in “Do I need another dose of COVID-19 vaccine?” question on this page).  Also, of note, if the virus continues to change, new variants may be able to evade immunity generated by vaccination, which would also affect the duration of protection. For more details about this, see Dr. Offit’s video, “What Should I Know About COVID-19 Vaccine Boosters?”

Last updated: Jan. 24, 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, some studies have suggested that infection followed by vaccination provides better protection than either vaccination or infection alone.

Watch this short video in which Dr. Offit discusses what is known about COVID-19 reinfection.

Last updated: Jan. 24, 2022

Could taking two different vaccines boost the effectiveness?

Currently, the Centers for Disease Control and Prevention (CDC) recommends getting two doses of the same mRNA vaccine unless the supply does not allow for doing so.

People are also recommended to get the same brand for the third dose of mRNA vaccine if they are receiving it because of an immune-compromising condition. However, if they are receiving a second dose following J&J/Janssen or a third dose following mRNA as a booster, they can get a different type if they so choose. The CDC recommends getting mRNA vaccines when possible unless an individual requires or prefers J&J/Janssen for a particular reason or if the supply limits one’s choice.

Last updated: Jan. 24, 2022

Is a coronavirus vaccine necessary?

SARS-CoV-2 infections can be a minor hindrance or lead to severe disease or even death. 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: Dec 15, 2020; reviewed Jan. 25, 2022

How long before a coronavirus vaccine takes effect?

The mRNA vaccines require two doses. While people will have some immunity after the first dose, protection will be most likely about one week after receipt of the second dose and the individual will be considered “fully vaccinated” two weeks after the second dose. Most individuals are recommended to get a third dose at least five months after the second dose to further bolster their immunity.

The adenovirus vaccine (Johnson & Johnson/Janssen) requires one dose. While people will have some immunity about two weeks after being vaccinated (and be considered “fully 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.

Last updated: Jan. 25, 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. To date, most of the changes have allowed for easier spread or had minor effects on vaccines or treatments. So far, none of the variants have changed enough that they require new vaccines; however, scientists are working on vaccines that would be able to protect against the most concerning variants in case additional doses become necessary and recently Pfizer announced that it is working on an omicron-specific version. However, the original Pfizer mRNA vaccine remains effective against severe disease and death for most people.

Read more about why variants are concerning to scientists, why they should concern individuals, and how they are classified in this article from the April 2021 Vaccine Update for Healthcare Providers.

Watch this video in which Dr. Hank Bernstein provides more information about coronavirus mutations and the COVID-19 vaccines.

Last updated: Jan. 25, 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

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

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 getting the first dose, but before getting the second dose, she can still get the second dose on time, 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: Jan. 25, 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

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

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

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. 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: Mar. 18, 2021; reviewed Jan. 25, 2022

Is the coronavirus vaccine being studied in children?

Yes. The Pfizer mRNA vaccine is now approved for use in those 5 years of age and older. Studies of the Pfizer vaccine are ongoing in those younger than 5 years of age. The Moderna and J&J/Janssen vaccines are also being studied in those younger than 18 years of age.

It is important that COVID-19 vaccines be thoroughly tested in children before they are given in this group because we cannot assume that they will act the same way in younger children, particularly since we have seen that children are not affected in the same way by COVID-19 infections.

Last updated: Nov. 10, 2021; reviewed Jan. 25, 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 an additional dose.

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 both doses (if they receive the mRNA vaccine) and possibly a third dose, depending on their condition (See “Do I need another dose of COVID-19 vaccine?” for more details). They may also choose to practice other public health measures until more is known about their protection against SARS-CoV-2, the virus that causes COVID-19.

Last updated: Nov. 10, 2021; reviewed Jan. 25, 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 mRNA or adenovirus vaccine, as long as they do not have another condition that puts them among the people recommended against vaccination. While a small number of cases of GBS have been identified following receipt of the adenovirus-based COVID-19 vaccine (J&J/Janssen), the cases have been rare (about 1 of 100,000 people) and COVID-19 remains widespread, so the benefits still outweigh the risks.

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: Jan. 25, 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 Jan. 25, 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 Jan. 25, 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 Jan. 25, 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 mRNA or adenovirus-based 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 Jan. 25, 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 mRNA and adenovirus-based vaccines 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: Jan. 25, 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 Jan. 25, 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 Jan. 25, 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 Jan. 25, 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:

Last updated: Jan. 25, 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

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. Additional resources related to COVID-19 vaccination of young children are also shared in the accompanying News & Notes article.

Last updated: Jan. 25, 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 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 took into account 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.

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: Jan. 25, 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 Jan. 25, 2022

Does the COVID-19 vaccine contain blood products?

The COVID-19 mRNA and adenovirus vaccines 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 Jan. 25, 2022

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

Several tools have been developed to help public health officials, governments, businesses, and individuals make informed decisions. These tools use county-level data to provide guidance. Two that may be particularly helpful include:

  • COVID-Lab: Mapping COVID-19 in your community — Developed by PolicyLab at Children’s Hospital of Philadelphia, this tool allows you to see COVID-19 test positivity in counties throughout the United States. The tool also offers projections for how levels of disease are expected to change in the next four weeks based on current social distancing practices, population density, testing capacity, and anticipated temperature and humidity.
  • COVID-19 event risk assessment planning tool — Developed by teams at Georgia Institute of Technology and Applied Bioinformatics Laboratory, this tool offers information about gatherings by county throughout the U.S., showing 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: Dec. 15, 2020; reviewed Jan. 25, 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 Jan. 25, 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 Jan. 25, 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 Jan. 25, 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.

Last updated: Dec. 15, 2020; reviewed Jan. 25, 2022

COVID-19 video resources

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

Do We Need a COVID-19 Booster Dose?
Vaccine Education Center (VEC) “Current Issues in Vaccines” webinar presented by Dr. Paul Offit on Dec. 8, 2021 describes some of the considerations and data related to booster dosing. (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.)

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: Jan. 25, 2022

Reviewed by Paul A. Offit, MD on January 25, 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.