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 on our printable Q&A, "COVID-19 mRNA vaccines: What you should know" (also available in Spanish and Japanese) and our “Look at Each Vaccine: COVID-19 Vaccine” webpage.

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. (See more about dendritic cells and the adaptive immune system in this animation.)

Last updated 12/15/2020

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 puts 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.

Last updated: 3/1/2021

Who should NOT get the COVID-19 vaccine?

Most people are able to get the COVID-19 vaccine, once supplies allow for their priority group to be vaccinated. But, a few groups of people should not get the vaccine, and some others should consult with their doctor or follow special procedures.

People who should NOT get the COVID-19 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, a vaccine component, or polysorbate
  • Those younger than 16 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.

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.)
  • Pregnant women
  • People with certain immune-compromising conditions
  • Breastfeeding women
  • People on anticoagulants

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.
  • 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).
  • People who got another vaccine (non-COVID-19 vaccine) should wait at least 14 days before getting COVID-19 vaccine. Likewise, if a person got the COVID-19 vaccine, they should wait at least 14 days before getting any other vaccines (non-COVID-19 vaccines).

Last updated 12/31/2020

Where can I get the vaccine?

Each state has their own plan for vaccine distribution. While these plans are based on guidance from the CDC, each is a bit different to accommodate the unique needs of their populations as well as to account for disease statistics in their area, number of doses of vaccine they expect to receive, etc. As such, we suggest checking your state health department website as most states have put their plans on their website. Some states also have opportunities to sign up for text or email alerts to stay abreast of COVID-19 vaccine distribution information.

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: 3/1/2021

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. Side effects were more frequent following the second dose and more likely to be experienced by younger, rather than older, recipients. 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.

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.

Last updated 3/1/2021

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 for the mRNA vaccines develop over a week or two after vaccination and for the adenovirus vaccines 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.

Last updated: 3/1/2021

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: 3/1/21

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 pretty 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.”

  • 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.

Last updated: 3/1/2021

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 consider 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.

Last updated: 2/1/2021

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: 3/1/2021

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. You still only need to get the second dose. However, it is important to note that 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.

Last updated: 1/19/2021

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).

Last updated: 3/1/2021

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: 3/1/2021

Can my second dose of the COVID-19 mRNA vaccine be from a different company?

The CDC has recommended that people get the same version because that is what the data in the clinical trials were based on. However, they have indicated that “in exceptional circumstances” if the same version is not available, a person can, for example, get the Pfizer vaccine first and the Moderna vaccine second. The two doses should be separated by at least 28 days if different brands are used. However, people who got the first dose of an mRNA vaccine should not switch to the adenovirus version (Johnson & Johnson/Janssen). The best-case scenario would be that most people will be able to get the second dose from the same vaccine maker as their first dose.

Last updated: 3/1/2021

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) recommends 14 days between receipt of a COVID-19 and non-COVID-19 vaccine, regardless of the order in which they are received.

Last updated: 1/19/2021

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

While younger children do not appear to be as easily infected with SARS-CoV-2, they can still be infected. Therefore, if a parent tests positive, they should still try to isolate from other members of the household, and all others in the home, including any children, should quarantine and be monitored for symptoms, as per CDC recommendations for exposure. The CDC has a dedicated page with guidance for situations in which a parent tests positive.

Last updated: 1/19/2021

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

The mRNA and adenovirus vaccines are not composed of live viruses, so there is no infectious virus to spread from a vaccinated person to someone else. But, we do not yet know if a vaccinated person who encounters the virus can still experience what is referred to as “asymptomatic infection.” An asymptomatic infection occurs when a person is exposed to the virus in the community and the virus can still replicate in their body, but they don’t have symptoms because their immune system stifles the infection as a result of vaccination. In this scenario, the person could potentially spread the virus without even knowing they are infected.

Given that families may not all get vaccinated at the same time, those who have been vaccinated should continue to practice public health measures when they are out in the community to decrease the chance of introducing the virus in the home through asymptomatic infection. Likewise, even when a whole family is vaccinated, continuing to practice these measures will be 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 been vaccinated to slow the spread of the virus, we will all be able to move away from these public health measures. But, for now, we need to continue working together to decrease spread of the virus by masking, physical distancing, handwashing, and getting vaccinated.

Read more in the January 2021 Parents PACK newsletter article, “When the Whole Family Has Not Yet Been Vaccinated Against COVID-19.”

Last updated: 3/1/2021

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.

Last updated 2/19/2021

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 – low levels of fetal cell debris, amino acids

NOT in the COVID-19 adenovirus vaccines:

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

Last updated: 3/1/2021

Do COVID-19 vaccines contain antibiotics?

No. Neither the mRNA vaccines (Pfizer and Moderna) nor the adenovirus vaccine (Johnson & Johnson/Janssen) contain antibiotics.

Last updated: 3/1/21

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 of Dr. Offit describing how mRNA vaccines work.

Last updated 12/15/2020

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: 3/1/2021

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.

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.

Last updated 3/1/2021

How well do the COVID-19 vaccines work?

All three COVID-19 vaccines approved for use in the U.S. work well, and individuals should get whichever one they are able to get in order to protect themselves from COVID-19 as soon as possible.

  • mRNA vaccines: More than 9 of every 10 people vaccinated during the clinical trials were protected from disease.
  • Adenovirus-related vaccine: While only about 6 or 7 of every 10 people vaccinated during the clinical trials were protected from disease, the study found that 8 or 9 were protected from severe disease and all were protected against hospitalization by one month after vaccination. Also, studies of the mRNA and adenovirus vaccines were done on different populations, making it difficult to compare these vaccines. Whereas all of the mRNA studies were done in the United States, the adenovirus vector vaccine (Johnson & Johnson/Janssen) studies were performed in Latin America, South Africa and the United States. Because the viral strains circulating in South Africa and Latin America were different from those circulating in the United States, it’s difficult to directly compare the relative efficacies. 

Last updated 3/1/2021

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 1/19/2021

Once I have been vaccinated against coronavirus, am I exempt from lockdown restrictions?

Everyone will still need to practice recommended public health measures for a while because it will take some time to slow or stop the spread of the virus. Two factors are important for understanding why:

  • While the vaccines appear to be highly effective at preventing disease, they might not prevent asymptomatic infection, meaning vaccine recipients might still be able to get infected, but not have symptoms and, therefore, unwittingly spread the virus. The companies are doing additional studies to better understand whether this is the case.
  • Scientists estimate that to control COVID-19, about 6 of every 10 people will need to be immune. Given that the U.S. population is more than 330 million people, this means that almost 200 million of them will need to be immune to reach this goal. By February 2020, the CDC estimates that about 83 million people in the U.S. were infected and about 55 million people received at least one dose of vaccine. But, these numbers have some overlap given that previously infected people are also being vaccinated. As such, many millions more individuals have to become immune before we can reach population immunity. 

For these reasons, there will still be some period of time during which other measures, such as masks, social distancing, and other public health measures, will be required to slow or stop the spread of the virus. And, because we won’t know who might still be able to be infected after vaccination or previous illness, everyone will be asked to comply. Watch Dr. Offit discuss the continued need for masks and social distancing in this short video.

Last updated 3/1/2021

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: 12/31/2020

Do you know if the COVID-19 vaccines contain live virus?

None of the early vaccines (those by Moderna, Pfizer, AstraZeneca, or Johnson & Johnson/Jannssen) are live weakened versions (similar, for example, to the measles, mumps, rubella, or varicella (chickenpox) vaccines). Moderna’s and Pfizer’s are mRNA vaccines, and AstraZeneca’s and Johnson & Johnson/Jannssen’s are non-replicating vectored vaccines. You can learn more about the different types of vaccines being tested in the response to “What types of COVID-19 vaccines are being tested?”

Last updated 12/15/2020

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.

Last updated 3/1/2021

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

The mRNA vaccines require two doses. For the Pfizer vaccine, doses should be separated by 21 days. For Moderna’s vaccine, doses should be separated by 28 days. The two mRNA vaccines are not interchangeable. A person should be sure they know which one they got as the first dose and be clear about when they should return for the second dose, particularly because the vaccines require both doses to have the best protection.

The adenovirus vaccine (Johnson & Johnson/Janssen) only requires a single dose.

Last updated 3/1/2021

Will booster doses or annual vaccines be needed?

Since the first people in the trials were vaccinated at the end of July 2020 and the first vaccines were approved in December 2020, we only have information about protection against disease for a few months after vaccination. Trial participants will continue to be monitored, so we will learn more, but we do not yet know whether booster doses will be needed.

Further, the increased presence of variants might affect whether or how often additional doses would be needed. Scientists are continuing to monitor variants and the ability of currently available vaccines to protect against them.

Last updated 3/1/2021

How long will vaccine immunity last?

We do not yet know how long immunity lasts after infection or vaccination:

  • Infection - Right now, scientists feel confident that 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.
  • Vaccination - Since the first vaccines were given in clinical trials that started in July 2020 and they were approved based on data generated through early December 2020, we know that immunity is likely to last for a few months. However, these people are continuing to be monitored, so that over time, scientists will learn more about the durability of immune responses to vaccination. Based on the elements of the immune response activated after vaccination with either the mRNA or adenovirus vaccines, it is likely that immunity will be long-lived. But, time will tell, and if the virus changes in a way that evades immunity generated by vaccination, that would also affect the duration of protection.

Last updated 3/1/2021

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. The vaccine trials included people who were previously infected with SARS-CoV-2, and the vaccine was found to be safe. Because we do not know how long antibodies last after infection and a small number of people have had more severe second bouts of infection, the vaccine can be beneficial in boosting a person’s existing immunity from infection.

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

Last updated 12/15/2020

Can we give COVID-19 vaccine to a person sick with COVID-19?

People who currently have COVID-19 should wait until they have recovered and meet the criteria to stop isolating.

If a person had antibody therapy as part of their treatment, they should wait for 3 months before getting the vaccine.

Last updated 12/15/2020

If a person is vaccinated against COVID-19, will they be able to spread the virus to susceptible people?

People will not spread the virus after vaccination with the mRNA or adenovirus vaccines since they are not live vaccines that reproduce the whole virus in the body.

But, we do not yet know if these vaccines prevent infection or if they only prevent disease:

  • Disease means people experience symptoms of illness.
  • Infection means that a virus can infect a person’s cells and reproduce, but the person may or may not have symptoms or be contagious.

If the COVID-19 vaccines only prevent disease, a person could be infected following an exposure and potentially spread the virus. Additional studies are underway to determine whether the vaccines prevent infection as well as disease. However, given this uncertainty, vaccinated people will still need to use masks and practice social distancing measures for some time.

Last updated 3/1/2021

Could taking two different vaccines boost the effectiveness?

Currently, COVID-19 vaccines are not interchangeable. However, if a person gets one of the mRNA vaccines and the supply does not allow for them to get the second dose of the same brand, they can get the other mRNA vaccine, with the second dose at least 28 days after the first one. This should only be done in extenuating circumstances.

Additional studies are required because three scenarios can occur if a person gets vaccinated with two versions of vaccines against the same disease, particularly close in time:

  • They get a stronger immune response. An example of this was when children got inactivated polio vaccine and later got oral polio vaccine.
  • The second vaccine causes immunity that would be similar to receiving a second dose of the original vaccine. Using a different brand of hepatitis B vaccine for one or more doses would be an example of this.
  • The immune response generated by the first vaccine interferes with components of the response to the second vaccine, in some cases causing lower immunity. For example, when people got a pneumococcal polysaccharide vaccine (PPSV) followed by a pneumococcal polysaccharide vaccine with a harmless helper protein attached to it, called pneumococcal conjugate vaccine (PCV), they had lower antibody responses to one part of the PCV vaccine than people who got the two vaccines in the opposite order (PCV followed by PPSV).

For these reasons, studies will be important for determining the effects of getting a second type of COVID-19 vaccine shortly after receiving a different one. If, however, we find that COVID-19 vaccines are like influenza vaccines and we need to get vaccinated annually, concerns about switching types from one year to the next are less likely to be an issue.

Last updated 3/1/2021

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.

Last updated 12/15/2020

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.

The adenovirus vaccine (Johnson & Johnson/Janssen) requires one dose. While people will have some immunity about two weeks after being vaccinated, protection will be more robust about one month after receipt of the vaccine.

Last updated 3/1/2021

Does the mutation of coronavirus affect the capacity of vaccines to prevent disease?

Viral mutations can cause vaccines to be less effective, such as we see with the influenza virus, so it is reasonable to wonder whether changes to SARS-CoV-2 will affect COVID-19 vaccines. Although SARS-CoV-2 is constantly mutating, the critical question is does the virus’s mutation change function, making the virus more or less virulent or more or less contagious. While some variants seem to be more transmissible and some evidence suggests that a few also cause more severe disease, currently, the vaccines and immunity that exists from previous infection still seem to protect people from severe disease or death. However, scientists are continuing to monitor these variants, and vaccine manufacturers have already started working on revised vaccines in case the current vaccines stop being effective.

Last updated 3/1/2021

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 immunized since the COVID-19 mRNA vaccines became available, and many of them are also being monitored through the CDC’s V-safe program. The good news is that in these women, no concerns were found and the vaccine worked, but pregnant women will continue to be monitored.

Despite the limited amount of data, both the Centers for Disease Control and Prevention (CDC) and the American College of Obstetricians and Gynecologists (ACOG) have recommended that pregnant women who are part of a group recommended to get the COVID-19 vaccine may be vaccinated if they choose to do so. These women should be supported in their decision-making efforts by their doctors and be provided with information related to the potential risks and benefits, but they do not have to wait to have a consultation with their healthcare provider before being vaccinated if they are comfortable doing so.

Two factors, in addition to the limited vaccine data, were important for informing these recommendations. First, some pregnant women will be at high risk for COVID-19, such as healthcare workers or those with certain health conditions. Second, pregnant women are at increased risk of developing complications, compared with their non-pregnant peers, when infected with COVID-19.

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

  1. Pregnant women who decide to 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 whether or not a pregnant woman decides to be vaccinated, she should practice recommended public health measures, particularly because of the increased risk to pregnant women infected with COVID-19.

Last updated 3/1/2021

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

Yes. Although women who are breastfeeding were not included in the clinical trials, current data suggest 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 after they have been vaccinated.

The baby may also benefit from antibodies or immune cells that may be 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 have made statements in support of this approach.

Last updated 1/25/2021

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 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.

Last updated 12/15/2020

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

No, you do not need to delay pregnancy. But, if you become pregnant within 30 days of receiving a dose of vaccine, you should consider registering for V-safe, a mobile-app based program being offered by the CDC that is tracking the safety of COVID-19 vaccines.

Last updated 3/1/2021

Will getting the COVID-19 vaccine affect my menstrual cycle?

We have not heard of disruption of menstruation cycles following receipt of the COVID-19 vaccine, nor would there be a biological theory to explain why this would happen. 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.

One possible explanation for a change in timing of one’s menstrual cycle would be that stress can cause changes to hormone levels, which in turn can alter a person’s schedule; however, we would suggest that concerns about changes to a woman’s cycle be discussed with the individual’s gynecologist, who has the benefit of access to the person’s medical history and current situation to help sort out what might be going on.

Last updated: 3/1/2021

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

Some people experience swelling of lymph nodes under their arm after getting the COVID-19 mRNA vaccine, which on occasion has been falsely identified as spread of breast cancer to lymph nodes. Therefore, delaying the mammogram can prevent the chance of this happening.

Last updated: 3/1/2021

Is the coronavirus vaccine being studied in children?

Yes. Studies of COVID-19 vaccines in children have started. The Pfizer mRNA vaccine was tested in some 16- to 18-year olds and has been approved for teens in this age group. As more information becomes available in younger children and teens, the age-related recommendations will be adjusted.

It is important that COVID-19 vaccines be thoroughly tested in children younger than 18 years of age before they are given in this group because we cannot assume that they will act the same way in children. This will be particularly important since we have seen that children are not affected in the same way by COVID-19 infections.

Watch this short video in which Dr. Offit discusses testing COVID-19 vaccines and children.

Last updated: 3/1/2021

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. Data about how well the vaccine works and its safety in immune-compromised individuals are not currently available, so it is possible that these individuals could have a lower immune response to vaccination. On the other hand, persons with these conditions may also be at higher risk of severe disease due to COVID-19. Therefore, the CDC recommended that people who are immune-compromised or taking immunosuppressive medications could receive the vaccine if they wanted as long as they do not have other contraindications.

With this said, 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 practice other public health measures until more is known about their protection against SARS-CoV-2, the virus that causes COVID-19.Post-licensure monitoring systems, like the Vaccine Adverse Events Reporting System (VAERS) and the Vaccine Safety Datalink (VSD), will be used to allow  for real-time monitoring of these sub-groups.

Last updated 3/1/2021

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. COVID-19 and influenza (flu) vaccines are made differently. Likewise, influenza (the disease) can cause GBS, but SARS-CoV-2, the virus that causes COVID-19, has not been suggested as a cause of GBS, so it would not be expected that the vaccine could cause it either.

In addition, 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 about vaccines and GBS.

Last updated: 3/1/2021

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: 3/1/2021

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

Patients on blood thinners are asked to speak with a healthcare provider because the vaccine is given intramuscularly, which increases the risk for bleeding. The vaccine itself does not increase the risk for this group of patients.

Last updated: 1/25/2021

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.

Last updated: 3/1/2021

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 does 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.

Last updated: 3/1/2021

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.

Last updated: 1/25/2021

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: 1/25/2021

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.

Last updated: 1/25/2021

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), a previous dose of COVID-19 vaccine, or to polysorbate should not get the COVID-19 mRNA vaccines.

People with severe allergies 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 recently 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.

These numbers suggest that while people with allergies have a somewhat greater risk of having a severe reaction to the COVID-19 mRNA vaccine than someone with no identified allergies, the risk remains very low — about 3 of 100,000 people with allergies would be expected to have a severe allergic reaction, compared to about 3 of 1 million people without allergies. Or, said another way, people with previously identified allergies are at only slightly greater risk than the person standing in front of or behind them in line.

The CDC publication can be reviewed here, and the CDC will continue to monitor allergic reactions and update their guidance if new findings come to light.

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: 1/19/2021

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.
  • The protein itself is too large to cross the BBB.

Adenovirus vaccine:

  • The virus is too large to cross the BBB.

Last updated 3/1/2021

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

Antibody-dependent enhancement (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 will not be 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.
  • Finally, when people with COVID-19 received plasma containing SARS-CoV-2 antibodies, they did not experience enhanced disease.

For these reasons, ADE is not expected to be a concern for SARS-CoV-2 infections or vaccination.

Last updated 12/15/2020

Does the COVID-19 vaccine cause fertility issues?

Infertility has not been found to be an issue in women infected with COVID-19, so it would not be expected to be a concern for the vaccine.

Concerns about antibodies generated by the COVID-19 vaccine attacking syncytin-1, a protein associated with the placenta during pregnancy, are unfounded. The claims, which circulated online, were based on a small number of similar amino acids in the two proteins, but the overlap is not sufficient to cause such a reaction. This notion has been addressed by Full Fact.

Last updated 12/15/2020

If I am currently staying in a state that is not my permanent residence, can I get the vaccine?

We recommend that you inquire with the Department of Health in the state that you are in to find out more specific information. While most states are not checking residency, a few are. You can find each state’s COVID-19 information on this page of the Vaccinate Your Family website.

Last updated 3/1/2021

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

People should separate their COVID-19 vaccinations by at least 14 days from any other vaccine (before or after). This recommendation is based on the fact that we currently do not have data regarding whether the COVID-19 vaccines will affect, or be affected by, other vaccines. Studies to determine whether COVID-19 vaccines can be given with the flu vaccine or the shingles vaccine will be completed; these types of studies are called “concomitant use studies.”

Last updated 12/15/2020

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 12/15/2020

How much will the coronavirus vaccine cost?

Coronavirus vaccines will be distributed for free; however, insurance companies may have to cover the cost of administering the vaccine.

Last updated 12/15/2020

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. 

Last updated 3/1/2021

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 12/15/2020

We don't talk about "herd immunity" for protection against influenza or other common viral infections, so why is it discussed so much with COVID?

Herd immunity is a concept used in public health to describe a situation in which the more people in a community immune to a particular pathogen, the fewer people available for that pathogen to infect. As the infectious agent spreads through a community, it has more trouble finding susceptible people if most of those around them are immune. In this manner, we rely on herd immunity for viruses, such as measles, rubella, polio, and chickenpox, among others, even if we are not having conversations about it. Influenza is more difficult because the virus changes so much from one year to the next and as such, vaccination does not offer long-term protection.

Related to COVID-19, herd immunity has been discussed more frequently for a couple of reasons. First, because this is a completely new virus, no one had pre-existing immunity. People can become immune to SARS-Co-V2, the virus that causes COVID-19, in two ways — through disease or through vaccination. By monitoring how many people are immune relative to the entire population, public health officials can offer informed guidance related to easing restrictions meant to stem spread of the virus.

Herd immunity can only be induced by vaccination. Never in history has any virus infection been eliminated because of immunity induced by natural infection.

Last updated 3/1/2021

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

While COVID-19 vaccines have been developed more quickly than has ever been done in the past, 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.

Last updated 12/15/2020

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 12/15/2020

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, and no studies have actually been completed to test this theory.

Last updated 12/15/2020

COVID-19 video resources

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

Update on SARS-CoV-2 vaccines
Vaccine Education Center (VEC) Current Issues in Vaccines webinar, Dec. 9, 2020 (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 nineteen short videos in which Dr. Offit addresses common questions about COVID-19.

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 3/1/2021

Reviewed by Paul A. Offit, MD on March 01, 2021

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.