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. 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.

Can't find what you're looking for? Ask your COVID-19 vaccine questions here.

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

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 is creating 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 the disease statistics in their area, number of doses of vaccines they expect to receive in the early days, etc. As such, we suggest checking your state health department website as most of the 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.

Last updated: 12/31/2020

What are the side effects of the mRNA vaccine?

Side effects from both mRNA vaccines are caused as part of the immune response to the vaccines. In some ways, the more vigorous the immune response, the more common the side effects.

The most common side effects from the mRNA vaccines 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.

Last updated 12/15/2020

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 develops over a week or two after vaccination, but the greatest chance of affecting your immune response would be in the first few days after receipt of the vaccine.

Last updated: 1/20/2021

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 had a fever, but we know that the vaccine worked for 90 of every 100 people.

Last updated: 1/20/21

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

The vaccine is not expected to have long-term negative effects for a few reasons:

  • First, 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.
  • Second, 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.

Last updated: 12/31/2020

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

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 the child, 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 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: 1/8/2021

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 1/19/2021

Do mRNA vaccines contain antibiotics?

No. Because the mRNA vaccines do not involve growing SARS-CoV-2 virus in cells to produce the vaccine, they do not contain antibiotics.

Last updated: 12/22/2020

When the Moderna vaccine first came out the CDC said it was 100% effective in older adults, now they are saying it is not as effective in older adults. Which information is true?

A few different concepts are at work here, so let’s look at each individually:

  • Regarding changing efficacy – The Moderna vaccine was originally reported to have 100% efficacy against severe disease. This report was a result of the fact that no people in the vaccine group had a severe case of COVID-19 when they pulled together their data to submit it to the FDA. Thereafter, one person in the vaccine group developed symptoms that could qualify as a “severe case of COVID-19,” according to their study definition. This person’s diagnosis meant the calculations changed, hence a lower efficacy. If we consider that vaccines are typically not 100% effective, we would expect that over time some people in the vaccine group would likely develop disease, but likewise, over time, more people in the placebo group would as well. So scientifically speaking, this change is not concerning.
  • Regarding lower efficacy in older adults –Moderna found 94.1% efficacy in all age groups, but only 86.5% in those over 65 years of age. The efficacy in older adults was calculated based on a very small number of vaccine recipients over 65 years of age getting the disease (4 of them) compared with the number over 65 in the placebo group who got sick (29). It is expected that, as with the Pfizer vaccine, people over 65 are well protected and that this perceived difference is reflective of the small numbers of older adults who experienced disease through that point in the trial. As the company continues monitoring trial participants, we will learn more.
  • With all of this said, it is important to be aware that as these vaccines start to be used in the general population, we will find lower levels of protection “in the real world.” You can think of this as being analogous to “gas efficiency” rates that we look at when we buy a car. What you see on the window sticker at the time of purchase is not necessarily what you experience when you buy the car because the actual number relies on how you and other consumers use your cars (e.g., highway versus local driving), whereas the manufacturer measures gas efficiency under strict conditions. In the case of vaccines, clinical trials represent well-controlled settings compared with general use in the population. This phenomenon is so well-known that scientists refer to “efficacy” and “effectiveness” when talking about how well a vaccine works.
  • Efficacy is what we know from a clinical trial
  • Effectiveness is what is experienced when the vaccine is used with the general public.

However, even if efficacy was 95% and effectiveness falls to 80%, that still means 8 of every 10 people who get vaccinated are spared from the disease.

You can read a comparison of the Moderna and Pfizer vaccines in this article.

Last updated: 12/22/2020

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

What stops the body from continuing to produce the COVID-19 spike protein after getting an mRNA vaccine?

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.

Last updated 12/31/2020

How well does the mRNA vaccine work?

More than 9 of every 10 people vaccinated during the clinical trials were protected from disease. This number may decrease a bit as the vaccines are given to the general population because the conditions during a clinical trial tend to be optimal, so they measure the best case scenario. However, it is still expected that most people who get both doses of the vaccine, according to the time interval recommended, will be protected.

Last updated 12/15/2020

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, it 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 will be doing additional studies to better understand whether this is the case.
  • Scientists estimate that to control COVID-19, about 7 or 8 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 250 million of them will need to be immune to reach this goal. Between March and November 2020, almost 12 million people in the U.S. were found to be infected, although estimates from antibody studies suggest that the number might be 3-7 times greater. Despite this the virus rages on, demonstrating just how many more people need to become immune before we can expect to control the spread of COVID-19. This also shows how important vaccines are in controlling the spread because more than 250,000 people died as a result of COVID-19 infections between March and November 2020. If we had to rely on infections alone to stop the spread of COVID-19, between 1 million and 5.4 million people would die on the way to 250 million people becoming immune.

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 12/15/2020

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

What types of COVID-19 vaccines are being tested?

Several approaches to COVID-19 vaccines are currently being tested. They include both tried-and-true as well as novel approaches.

Here is a brief summary of these different strategies:

  • Inactivated vaccine — The whole virus is killed with a chemical and used to make the vaccine. This is the same approach that is used to make the inactivated polio (shot), hepatitis A and rabies vaccines.
  • Subunit vaccine — A piece of the virus that is important for immunity, like the spike protein of COVID-19, is used to make the vaccine. This is the same approach that is used to make the hepatitis and human papillomavirus vaccines.
  • Weakened, live viral vaccine — The virus is grown in the lab in cells different from those it infects in people. As the virus gets better at growing in the lab, it becomes less capable of reproducing in people. The weakened virus is then used to make the vaccine. When the weakened virus is given to people, it can reproduce enough to generate an immune response, but not enough to make the person sick. This is the same approach that is used to make the measles, mumps, rubella, chickenpox and one of the rotavirus vaccines.
  • Replicating viral vector vaccine — In this case, scientists take a virus that doesn’t cause disease in people (called a vector virus) and add a gene that codes for, in this case, the coronavirus spike protein. Genes are blueprints that tell cells how to make proteins. The spike protein of COVID-19 is important because it attaches the virus to cells. When the vaccine is given, the vector virus reproduces in cells and the immune system makes antibodies against its proteins, which now includes the COVID-19 spike protein. As a result, the antibodies directed against the spike protein will prevent COVID-19 from binding to cells, and, therefore, prevent infection. This is the same approach that was used to make the Ebola virus vaccine. (To see how viruses reproduce in cells, watch this short animation.)
  • Non-replicating viral vector vaccine — Similar to replicating viral vector vaccines, a gene is inserted into a vector virus, but the vector virus does not reproduce in the vaccine recipient. Although the virus can’t make all of the proteins it needs to reproduce itself, it can make some proteins, including the COVID-19 spike protein. No currently licensed vaccines use this approach.
  • DNA vaccine — The gene that codes for the COVID-19 spike protein is inserted into a small, circular piece of DNA, called a plasmid. The plasmids are then injected as the vaccine. No currently licensed vaccines use this approach.
  • mRNA vaccine — In this approach, the vaccine contains messenger RNA, called mRNA. mRNA is processed in cells to make proteins. Once the proteins are produced, the immune system will make a response against them to create immunity. In this case, the protein produced is the COVID-19 spike protein. The Pfizer and Moderna COVID-19 vaccines use this approach. Watch this short video in which Dr. Offit discusses how mRNA vaccines work.

Hear more about the types of vaccines being tested in this recorded event presented by Dr. Offit, Director of the Vaccine Education Center Current Issues in Vaccines, December 9, 2020. This webinar series is supported by the Thomas F. McNair Scott Endowed Research and Lectureship Fund and co-sponsored by the PA Chapter, American Academy of Pediatrics and Wilkes University. (For healthcare providers wishing to obtain continuing education credits for viewing this recorded event, please review the continuing education information on this page.) View answers to a series of questions asked during the event.

You can also visit the Vaccine Makers Project page, “The Coronavirus Pandemic – Answering Your Questions” for more details about the types of vaccines being studied. (See the “April 6” entry), or watch this CNBC interview with Dr. Offit for animations showing how some of these approaches work.

Last updated 12/15/2020

Which type of COVID-19 vaccine is most likely to work?

It is likely that more than one of these approaches will work, but until large clinical trials are completed, we won’t know for sure. Likewise, the different approaches may have different strengths and weaknesses. For example, mRNA or DNA vaccines are much faster to produce, but neither has previously been used to successfully make a vaccine that has been used in people. On the other hand, killed viral vaccines and live, weakened viral vaccines have been used in people safely and effectively for many years, but they take longer to produce.

In addition to differences in how long it takes to make different types of vaccines, each type may also cause the immune system to respond differently. Understanding the immune responses that are generated will be important for determining whether additional (booster) doses will be needed, how long vaccine recipients will be protected, and if one type offers benefits over another.

Last updated 12/15/2020

Is one of the COVID-19 vaccines expected be more effective for the elderly population? 

Each vaccine will need to be tested in various age groups; however, both the Pfizer and Moderna mRNA vaccines worked well in older adults.

Some of the traditional approach vaccines may not be effective in elderly populations. But if that is found to be the case, alternative versions may be explored, such as higher dose versions, as was done for influenza vaccines. Another possibility would be to deliver the SARS-CoV-2 spike protein with one or two powerful adjuvants, similar to what was done with the shingles vaccine, known as Shingrix®, which works well in the elderly.

Last updated 12/15/2020

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

None of the early vaccines (those by Moderna, Pfizer, AstraZeneca, or Johnson & Johnson) 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’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, a few of the other vaccines being studied use cells originally isolated from fetal tissue (often referred to as fetal cells). These fetal cells are used to grow the vaccine virus. Some of these potential vaccines are currently being tested in people.

The fetal cells being used to produce some of the potential COVID-19 vaccines are derived from two sources (HEK-293 and PER.C6), neither of which is 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 cell lines are used to make two of the non-replicating viral vector vaccines being evaluated.

Check this article in Science for a table showing some of the candidate vaccines that use these cell lines and to learn more about a letter to the Food and Drug Administration (FDA) discouraging use of these cell lines for COVID-19 vaccine production.

Last updated 12/15/2020

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.

Some COVID-19 vaccines being evaluated only require a single dose, but the clinical trials will provide more information about how many doses of each vaccine will be needed.

Last updated 12/15/2020

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. The degree to which these vaccines protect against COVID-19 one or two years after vaccination will be determined later. Trial participants will continue to be monitored, so we will learn more, but we do not yet know whether booster doses will be needed.

Last updated 12/15/2020

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. Likewise, although the virus has been changing since it was first recognized, antibodies from people who were sick early during the pandemic are still effective against the slightly modified version. For these reasons, scientists are hopeful that people will be protected for one or more years.
  • 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 the mRNA 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 1/19/2021

If you had the virus, will 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 vaccines since they are not live vaccines that reproduce the whole virus in the body.

But, we do not yet know if the COVID-19 mRNA 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 mRNA vaccines only prevent disease, a person could be infected following an exposure and potentially spread the virus. Additional studies will be completed 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 12/15/2020

If more than one vaccine becomes available, could taking two different vaccines boost the effectiveness?

At least at first, COVID-19 vaccines are not be interchangeable. 

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 need to be done to determine 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 12/15/2020

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.

Last updated 12/15/2020

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. So far, the virus that causes COVID-19 does not appear to have functionally changed in an important way. But, it does happen and at some point a change could affect how well a vaccine works. Right now, that does not appear to be happening. For example, recent changes enabled the virus to spread more easily, but those changes do not appear to make people sicker and the vaccine appears to protect against the newer version. Likewise, antibodies from people who had an earlier version of the virus are still able to protect against the newer version. In other words, at least to date, the virus hasn’t mutated away from the approach taken to combat COVID-19 with vaccines.

Last updated 12/31/2020

What will be needed to obtain permission from the FDA for use of a coronavirus vaccine in the U.S.?

Vaccine manufacturers have to follow guidance provided by the Food and Drug Administration (FDA) while developing any coronavirus vaccine. This includes requirements to share information about how they determined that a vaccine is safe and that it works. Each company with a potential vaccine will need to provide data for review and information, so the FDA and other scientists can understand things like:

  • How the studies were designed
  • How many people were evaluated
  • How the testing to obtain the data was done

The FDA has also encouraged manufacturers to include people who represent the populations most affected by coronavirus in their studies, such as racial and ethnic minorities as well as older people and those with underlying illnesses.

Despite the shortened vaccine development timeline, the FDA has issued assurances that they will not approve a vaccine that was developed by sacrificing the standards for quality, safety, and efficacy that any other vaccine would need to meet. A group of vaccine manufacturers have also signed a pledge not to submit a COVID-19 vaccine before phase III studies have demonstrated that their candidate vaccine is safe and effective. The Biotechnology Innovation Organization (BIO) has also released an open letter to companies making COVID-19 vaccines regarding the standards that should be followed.

Last updated 12/15/2020

What are the phase III COVID-19 studies measuring to tell if a vaccine works?

The studies may be designed to measure slightly different things depending on the different companies:

  • Viral shedding – When people are infected with COVID-19, virus particles can be found in the secretions from their nose and mouth. Some studies are measuring whether vaccinated people have virus in these secretions, called viral shedding. With this approach, even if a person does not have symptoms, scientists can tell if the person was infected.
  • Protection against moderate or severe disease – In these studies, scientists evaluate people for specific symptoms of infection that are considered to represent more severe disease. By comparing the rates of these symptoms in people who were or were not vaccinated, they can tell if the vaccine protected more people from getting more severely ill. This is how the Pfizer and Moderna studies were done.
  • Some studies are evaluating both viral shedding and protection against moderate or severe disease.

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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. As a result, we only have a small amount of data regarding the safety of these vaccines in pregnant women. The good news is that in this small group of women, no concerns were found and the vaccine worked, but it will be important to get data on larger numbers of women moving forward.

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.

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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.

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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.

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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.

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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.

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 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.

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If a person is taking anticoagulants (blood thinners), can they 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: 1/19/2021

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 about 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 mRNA vaccine cross the blood-brain barrier?

It would not be expected that the mRNA vaccines would cross the blood-brain barrier for two main reasons:

  • 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.

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Does the mRNA 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.

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Does the mRNA 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.

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What company is working on coronavirus vaccine?

More than 150 groups around the world are working on coronavirus vaccines, including in the United States, United Kingdom, Germany, India, China, Russia, and South Korea. To find out more about the vaccines being tested, download the file found on this page of the World Health Organization’s (WHO) website.

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When will I be able to get a vaccine against COVID-19?

The U.S. Centers for Disease Control and Prevention (CDC) created a framework, informed by the efforts of other groups, to advise states regarding the equitable distribution of limited supplies of COVID-19 vaccines:

With this information states, territories, and local health departments each created their own prioritization plans and submitted them to the CDC. You can see the executive summaries of each plan on this page of the CDC’s website. However, these plans are continually being updated and adapted as more information becomes available. Therefore, you may wish to visit the website of your state, territory, or local department of health to find out more about what is happening in your area.

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If I am currently staying in a state that is not my permanent residence, will I be able to get the vaccine?

To our understanding, people will be able to get the vaccine where they are. We have not heard of states planning to check residence status before giving doses. However, you may want to inquire with the Department of Health in the state that you are in to find out more specific information. You can find each state’s immunization program website on this page of the Immunization Action Coalition’s website.

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How many doses of COVID-19 vaccine will be ready to give to people by the beginning of 2021?

Both Pfizer and Moderna have provided estimated doses, but the number of doses for the U.S. and how many doses will be allotted to various states and territories remains to be determined. Here is what is currently known:

  • Pfizer – 50 million doses by end of 2020 and 1.3 billion doses by end of 2021. These are global supply estimates, and the vaccine requires two doses, so about 25 million people could be immunized with the supply from late 2020 and 650 million by late 2021.
  • Moderna – 20 million dose for the U.S. by end of 2020 and 500 million to 1 billion doses by end of 2021. These are U.S.-based doses, and the vaccine requires two doses, so about 10 million people could be immunized with the late 2020 supply and 250 to 500 million people in 2021.

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Who will get the vaccine first?

In most states and areas throughout the U.S., it is expected that frontline healthcare providers and residents of long-term care facilities will be prioritized, followed by sectors of the population at higher risk of suffering severe disease and death, such as essential workers and those with health conditions that put them at higher risk.

State and local health departments are basing their plans on recommendations made by the Centers for Disease Control and Prevention (CDC):

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When will there be enough vaccine for everyone who wants to be vaccinated to get a COVID-19 vaccine?

While we cannot know for sure, if both the Pfizer and Moderna vaccines are provided in the quantities they estimate producing, it is expected that by summer or fall of 2021 most people who want a COVID-19 vaccine should be able to receive it, as long as they do not have a contraindication that prevents them from receiving these versions.

Likewise, it is possible that vaccines produced by Johnson & Johnson and AstraZeneca will become available during 2021 that could change these projections.

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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.”

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Since the vaccine has to be stored at such a cold temperature, what temperature will it be when it is given?

The vaccine will be thawed, allowed to come to room temperature, and diluted with a salt solution before being administered. Providers will be given specific instructions to ensure that how they handle the vaccine will not affect its effectiveness.

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How long after testing positive for COVID-19, can I get my flu shot?

Talk with your healthcare provider about when you personally can get your influenza vaccine, but generally speaking, people can get a flu vaccine once they no longer have symptoms of COVID-19. 

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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.

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Will getting the flu vaccine protect me against coronavirus?

No. Influenza viruses and coronaviruses are different, so the flu vaccine does not protect against coronavirus. You can learn more about the differences between these two viruses:

Even though flu vaccine does not protect against COVID-19, it is more important than ever to get an influenza vaccine this year:

  • For individuals — Preventing influenza infection will help people in two ways. First, since several of the symptoms of influenza and COVID-19 are similar, it will help with determining the cause of an infection this winter. Second, many people who die after having influenza actually die from a second infection. These second infections are called “opportunistic infections.” They are often the result of bacterial infections that capitalize on lung damage caused by influenza, leading to pneumonia. Given that COVID-19 also affects the lungs, it is possible that influenza infection could be complicated by COVID-19. It will take time to figure out the effects of these two infections on the lungs if they occur at or near the same time, so preventing or lowering the chance of influenza infection is important.
  • For healthcare systems — Every year, hundreds of thousands of people are hospitalized with influenza. Given that COVID-19 is already straining medical resources, it is possible that the impact of influenza and COVID-19 occurring at the same time will overwhelm healthcare systems, leading to both difficult decisions about how to best provide care and unnecessary deaths.
  • For communities — If both COVID-19 and influenza are spreading in communities and people are uncertain which they have, it could lead to excessive quarantines and shutdowns that contribute to an already fragile economic recovery. Likewise, from a public health standpoint, more people immunized against influenza will decrease its spread. So, overall, communities will be healthier, and community resources, such as EMTs, ambulances, public health, and related services will not be further overwhelmed by influenza.

Find out more and see tips for keeping your family healthy in the September 2020 Parents PACK article, “Coronavirus, influenza … Feel more in control this fall.”

Watch this short video in which Dr. Offit describes the importance of getting flu vaccine during the COVID-19 pandemic.

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Does the pneumonia vaccine work against coronavirus?

Vaccines against pneumonia, such as the pneumococcal, Haemophilus influenzae type b (Hib), and meningococcal vaccines, are not likely to protect against COVID-19 disease.

However, the pneumococcal, Hib, and meningococcal vaccines prevent other serious infections. For more information about these vaccines and the diseases they prevent, go to:

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Does the anthrax vaccine protect from coronavirus?

The anthrax vaccine has not been tested for any ability to provide protection against COVID-19 disease, nor would it be expected to do so.

The anthrax vaccine is not routinely recommended in the U.S., but some high risk groups of people are recommended to get it.  Find out more on the “A Look at Each Vaccine: Anthrax Vaccine” webpage.

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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.

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How do we know if COVID-19 vaccines are safe?

Given that COVID-19 vaccines were made more quickly than other vaccines, it is understandable to be concerned about their safety, but the following can provide reassurances:

  • Phase III trials for COVID-19 vaccines have been as large as those for other vaccines, including tens of thousands of participants. While these trials may not uncover rare adverse events (that occur in the millions), we can be comfortable that these trials were large enough to detect any major safety concerns.
  • For each new vaccine, the data from these large phase III vaccine trials will undergo several rounds of review by different, independent groups of experts in immunology, statistics, infectious diseases, virology, and vaccinology:
    • The trials are coded, so that the manufacturers do not know who got vaccine and who got placebo. During this time, an independent group of experts monitor the data to make sure that no concerning developments occur with trial participants.
    • Once the company submits the data to the Food and Drug Administration (FDA), an advisory committee of independent experts, called the Vaccine and Related Biologics Product Approval Committee (VRBPAC) reviews the data to evaluate vaccine safety and effectiveness. This committee provides advice to the FDA before a vaccine can be accepted.
    • Once a vaccine is approved by the FDA, the data undergo a third round of review, by yet another committee of experts. This group, called the Advisory Committee on Immunization Practices (ACIP), reviews the data and make recommendations to the Centers for Disease Control and Prevention (CDC) regarding who should or should not get the vaccine and when, based on the data.

As a result, by the time a vaccine can be given to any individual, the results of the phase III trials have been reviewed and discussed regarding their scientific merit by more than 50 independent experts, in addition to the scientists at the companies and their own trial advisory groups.

Watch this short video to hear Dr. Offit discuss how we will know a COVID-19 vaccine is safe.

COVID-19 vaccines will be approved using the FDA’s “Emergency Use Authorization (EUA)” process, rather than the typical “Biologics Licensing Application (BLA)” process, due to the emergency we face resulting from the pandemic. However, the main difference between these processes from the point of view of vaccines is that under the EUA process, the vaccines will be approved more quickly, so they can get to people faster. As such, companies will need to continue monitoring the trial participants and submit subsequent findings to the FDA. In reality, companies usually continue following participants, but the time difference here is that rather than having studied the vaccine for several years, it has only been studied for several months; therefore, the additional monitoring will be critical to continuing to understand the durability of immune responses to the vaccine.

To find out more about the emergency use authorization compared to the typical vaccine approval process, watch this interview with Dr. Offit posted by Medscape (October 27, 2020).

Finally, once a vaccine is approved and individuals are deciding whether to get it, they will also have access to information that summarizes the clinical trial findings, particularly related to any side effects found during the trials and who should or should not get the vaccine. In the U.S., a document called a Vaccine Information Statement, or VIS, is legally required to be presented before every dose of vaccine is given. While a COVID-19 vaccine will be approved outside of the normal process, because of the EUA protocol, a VIS, or similar document, should still be made available to provide the information that individuals will need to make informed decisions based on the known risks and benefits.

To read more about the history of the VIS, see “History of Vaccine Information Statements,” produced by the Centers for Disease Control and Prevention.

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Does the COVID-19 vaccine have any derivatives of red blood cells, white blood cells, plasma or platelets?

The mRNA vaccines do not contain any blood products. We will not know about the ingredients of other vaccines until each is submitted for approval, as companies are required to share this type of information.

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Can DNA vaccines change the DNA of a person?

DNA vaccines are among the types being tested to prevent COVID-19. DNA vaccines may offer an advantage to other types of vaccines because they do not need to use the virus to produce an immune response. Other DNA vaccines in development (including for influenza, HPV, and HIV) have been extensively tested in animals and people and shown to be safe.

Some people are concerned that DNA vaccines could change people’s existing DNA. While it is the case that the DNA from the vaccine is treated the same as human DNA in the cell, two points are worth considering. First, DNA vaccines have not historically worked as well as other types because it is difficult to get enough DNA introduced to the vaccine recipient to make a strong immune response. Second, even when it is introduced successfully, vaccine DNA only enters a few cells, which then produce viral proteins that, once released from the cell, activate the immune system to generate immunity.

As such, concerns related to a person’s DNA being altered by DNA vaccines are theoretical concerns without evidence. Since all vaccines are required to go through extensive testing before approval, the same standard will be applied to DNA vaccines as will be applied to any other COVID-19 vaccine.  Only then will we know whether DNA vaccines will be useful in protecting against COVID-19.

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How can our family safely celebrate the holidays?

The November 2020 issue of Parents PACK offered tips for families as they plan for the holidays. Topics addressed include advance planning, travel and lodging, and during- and after-event precautions.

Check out the article on this page or download a PDF for sharing.

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Will there be more shutdowns?

Stay-at-home orders have been used as a way to decrease the spread of COVID-19; however, it is unlikely that the country will experience widespread shutdowns like those implemented in the spring of 2020. Rather, it is expected that locally targeted public health measures will be “turned up” and “turned down,” depending on situations in each community.

With this said, the virus is currently spreading so rapidly that we may see many communities or larger geographic areas concurrently implementing measures to slow the spread, particularly as the holidays may increase an already “out-of-control” spread. Indeed, the CDC recently asked Americans not to travel during the Thanksgiving and Christmas holidays. The best way to decrease the need for restrictions is for communities to ban together when it comes to wearing masks and social distancing, particularly until enough people have been immunized to make it difficult for the virus to find susceptible people in the community.

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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.

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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, virtually no one has existing immunity. People can become immune to SARS-Co-V2, the virus that causes COVID-19, in two ways — through disease or through vaccination. Conversations have been about both of these concepts:

  • As vaccines are developed, one way to describe how well a vaccine works is to describe how many people would need to be immunized to achieve herd immunity.
  • Likewise, some people are talking about herd immunity because they want to get back to “normal” and are arguing to “make the herd immune” by just going about one’s business and letting people get infected. Unfortunately, there are dangers involved with this because:
    • The disease is more fatal than a virus like influenza
    • We don’t know who will become severely ill if infected
    • If too many people get sick at the same time, we will overwhelm medical resources
    • We don’t know everything we need to know about how long immunity lasts following infection; we don’t understand the long-lasting effects of infection; and we have limited treatments at this stage (although we are learning more every day)

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

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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.

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I heard something about MMR vaccine helping against COVID-19. Can you tell me what that is about?

Some have proposed that giving people a live weakened vaccine, such as MMR (measles, mumps, and rubella) vaccine, might lessen the severity of coronavirus disease, including swelling in the lungs and sepsis, an infection in the bloodstream. While there is some evidence that live weakened vaccines can induce immunity that can protect against other infections, any protection would not be specific. At this time, use of MMR, or any other live weakened vaccine, has not been studied as a way to prevent the complications of coronavirus in either animals or people, so it is not recommended. Further, because the protection would not be specific or long-lived, it would not be as useful as COVID-19 vaccines.

For more information about MMR vaccine, go to "A Look at Each Vaccine: Measles, Mumps and Rubella (MMR) Vaccine." 

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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

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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.

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Is there a cure for coronavirus?

No cure for coronavirus is available.

People who are mildly ill and recovering at home
Rest and drinking plenty of fluids are most important for people with mild cases of COVID-19. While over-the-counter medications can be used to make a person more comfortable, it is important to realize that often symptoms are the result of the immune response to infection. For example, fevers make the body a less “comfortable” environment for the virus to reproduce and allow the immune system to work better. So, treating fever can prolong illness. To learn more about fever, check out this downloadable question-and-answer sheet, or to find out more about fever and vaccines, check out this webpage.

Those recovering at home should be in touch with their healthcare provider for specific medical recommendations, and anyone having trouble breathing, or who quickly takes a turn for the worse, should seek immediate medical care. A monoclonal antibody treatment, called bamlanivimab, was recently approved for treatment of mild-to-moderate disease in those with high risk conditions.

It is also important for those with mild illness to still isolate from others in the home as they can still spread the virus.

People who are severely ill and require hospitalization
Healthcare providers have been learning more about ways to treat people who become severely ill. One medication, Remdesivir, has been shown to shorten the length of infection. Similarly, a drug called dexamethasone (a steroid) has been shown to be of benefit for people with pneumonia caused by SARS-CoV-2.

Treatment of hospitalized patients varies based on the symptoms and complications each patient experiences.

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How did the new coronavirus form?

In late 2019, a novel coronavirus, SARS-CoV-2, formed. This new virus had two important characteristics. First, it could cause severe disease and death in people. Second, it could easily spread from one person to another. Together with the fact that no one in the world was immune, these characteristics set the stage for the COVID-19 pandemic that quickly changed current life as we knew it.

As scientists around the world have diligently worked to help us understand this virus and the disease it causes, it is important to realize that we will continue to learn more about this virus for many years to come. But, we have learned some important things already:

  • For many people, disease will be mild. Some people will not experience any detectable symptoms. But, this is not true for everyone, and, as with other infections, science has not evolved to a point that we can predict who will become severely ill, experience complications, or die. This means, everyone should take the virus seriously — if not for themselves, then for those around them.
  • In some cases, groups of people are known to be at greater risk of suffering severe COVID-19. These include older adults and people of color as well as sub-groups of the population, like those with heart and lung disease, obesity, type-2 diabetes, and pregnant women.
  • And, for some people symptoms last extremely long, and lingering, long-term effects may also result, although this is another area that healthcare providers and scientists are still working to understand.
  • Finally, while healthcare providers are learning more every day about how to treat COVID-19, many medications and treatments are still being studied.

For these reasons, and because prevention is better than treatment, COVID-19 vaccines are essential to returning to some sense of normalcy. But, we can also work together using important public health practices to limit the illness, deaths, and societal damage SARS-CoV-2 seeks to sow.

Last updated 12/15/2020

What are the ways that we can prevent spread of COVID-19?

Coronaviruses spread through respiratory secretions, like saliva produced during coughing, speaking, and singing, and nasal secretions producing during sneezing or from a runny nose. Droplets from coughs or sneezes are often considered “large droplets,” meaning they don’t hang in the air for long. But, in some cases, small virus-containing droplets can remain in the air for longer periods of time. These are sometimes referred to as “aerosolized droplets,” and they are more contagious. Viruses present in either of these sized droplets can enter another person’s eyes, nose, or mouth and infect cells that line that person’s nose, throat, lungs, blood vessels, and intestines. As such, we can protect ourselves and decrease spread in these ways:

  • Handwashing – Because we touch so many things, we almost always have germs on our hands. If these viruses or bacteria are still infectious, we can easily inoculate ourselves, particularly if we touch our eyes, noses, or mouths with unclean hands.
  • Social distancing – Because respiratory droplets travel some distance after leaving our mouths or noses, staying further apart decreases the chance for particles containing viruses to then be breathed in or land on us. The speed and force with which a particle leaves the body determines how far it can travel before landing somewhere. So, droplets from a sneeze will travel further than those spread during speaking. While a particular distance is not guaranteed to protect someone, the Centers for Disease Control and Prevention (CDC) has recommended 6 feet. In enclosed spaces, like small rooms or cars, the chance for exposure increases; therefore, it is important to increase ventilation, by opening windows and not using recirculated air when possible.
  • Masks – While masks have been somewhat controversial, they do help to decrease the spread of this virus, particularly because it can spread through “small droplets,” which means you do not need to see the droplets for them to spread the virus. Masks primarily decrease the spread of virus by the person wearing them, but they may also somewhat reduce the chance of being infected.

Find out more about masks:
How to properly put on, take off, and clean masks, October 2020 Parents PACK
Images of correct and incorrect ways to wear masks as well as information about studies of different mask materials, Vaccine Makers Project News & Events, September 30, 2020

  • Disinfecting surfaces – When respiratory droplets land on surfaces, the viruses they carry remain infectious for hours to days, depending on the characteristics of the virus, the type of surface on which they land, and the surrounding environment. Because the virus can be spread in droplets not visible to the eye, regularly cleaning surfaces that are touched often or around which people often pass is important to decreasing viral spread.
  • Staying home when sick – As with other respiratory viruses, anyone with symptoms should stay away from others to decrease spread. If someone with symptoms coughs or sneezes, their respiratory secretions are likely to have even greater amounts of virus than someone without symptoms. Therefore, they may infect more people or the small number of people they infect may get a bigger inoculation, which could lead to more severe disease. In the case of COVID-19, people who know (or think) they have been exposed are also being asked to isolate because it is estimated that about 4 of 10 people who are infected do not develop symptoms.

Last updated 12/15/2020

What is a challenge study?

To see whether a vaccine works, scientists have to determine whether people who got the vaccine are less likely to get sick with the disease than those who were not vaccinated. They can do this in one of two ways:

  • If the pathogen is spreading in the community, they can see if fewer vaccinated people get sick.
  • But, if the pathogen is only spreading at low levels, they may not be able to tell because differences between vaccinated and unvaccinated people could simply be due to differences in exposure to the virus. In this situation, challenge studies can be used.

A “challenge study” is one that includes intentional exposure to the pathogen as part of the research plan. For example, a study volunteer might get vaccinated and a month after receiving the last dose be intentionally exposed to the pathogen. After exposure, the volunteer would be monitored for both symptoms of illness and the presence of a memory immune response, such as through the measurement and typing of antibodies in a blood sample. Challenge studies have been used in the past to determine the effectiveness of various influenza vaccines.

Challenge studies offers a few benefits:

  • As mentioned, they do not need to rely on disease spreading in the community to see whether the vaccine works.
  • Scientists know when the person was exposed to the pathogen.
  • They can control the exposure, so that the person is not likely to get severely ill if the vaccine did not work as expected.

However, challenge studies can have ethical and technological drawbacks that must be considered before being implemented:

  • By definition, this kind of study means volunteers are being intentionally exposed to a pathogen. If the vaccine does not work, some people could become severely ill, or even die.
  • Currently, for COVID-19, we have limited treatment options, so treating anyone from a study who becomes ill would be further hindered by these limits.
  • Scientists have an important responsibility when they choose the challenge strain of the pathogen. They need to choose a strain that will cause the immune system to respond, but not one that will cause severe illness. In the current COVID-19 situation, much remains to be learned about this pathogen, which complicates the choice of a challenge strain.
  • Also, under natural conditions, people will be exposed to different burdens of virus. As a general rule, the greater the amount of virus the worse the symptoms. Challenge studies, however, are likely to use only one dose of virus.

Watch this short video in which Dr. Offit discusses challenge studies.

Last updated 12/15/2020

What are the different phases of clinical trials (phase I, II, and III studies)?

Vaccine development typically follows a progression of increasingly larger studies to limit risk while learning about the potential vaccine. Every phase monitors safety of the potential vaccine, but each phase also has additional specific goals:

  • Phase I studies typically include fewer than 100 healthy adults and are designed to figure out if the potential vaccine generates an immune response. Watch a short CNN interview in which Dr. Offit discussed how to think about Phase I results (July 21, 2020).
  • Phase II studies typically include a few hundred healthy adults and are designed to figure out the optimal vaccine dose and vaccine production specifications and tests.
  • Phase III studies typically include tens of thousands of participants. Ideally, these participants represent the population of people who will be recommended to get the vaccine. These studies evaluate whether the vaccine works in the intended population, and because of the number of people who receive the potential vaccine, they are important for detecting side effects that may occur infrequently, and, therefore, might not have been found in the earlier phases. These are the last studies completed before a potential vaccine can be licensed. Early phase III trials of the COVID-19 vaccine were designed to include about 20,000 people who got the vaccine and 10,000 people who get a shot that doesn’t contain the vaccine (i.e., a placebo). Some companies, however, might do smaller phase III trials.
  • After approval, scientists continue to monitor vaccines in “post-licensure studies.” In this way, they can quickly become aware of any previously undetected issues of concern, so that vaccinations can be halted if necessary. The Vaccine Safety Datalink in the United States is designed to quickly pick up a safety problem once the vaccine has been administered to hundreds of thousands or millions of people.

For more details about each of these phases, visit the VEC’s webpage, “Making Vaccines: Process of Vaccine Development.”

For more details about the Vaccine Safety Datalink, visit the CDC’s webpage, “Vaccine Safety Datalink (VSD).”

Last updated 12/15/2020

How long does each phase of vaccine testing last?

The amount of time for each phase of vaccine development varies based on a variety of factors related to the vaccine being tested, the disease, and the way the studies are designed. But, generally speaking, phase I trials take about 1 to 2 years, phase II trials take 2 or more years, and phase III trials take 3 to 4 years to complete.

In the case of COVID-19 vaccines, this timeline was shortened by combining the phases of trials, decreasing the number of participants in the early phases of the trials, and adding tremendous resources to allow for faster completion. For example, the government invested in some of the potential vaccine candidates to allow for building the manufacturing facilities and making vaccine doses before it is was known whether the vaccine worked. For example, because the Pfizer mRNA vaccine worked and was safe, doses could be distributed shortly after the vaccine was approved for use, but if the vaccine did not work, the doses would have been discarded.

You can find out more here:

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 eight 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 12/15/2020

Reviewed by Paul A. Offit, MD on January 20, 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.