Archived COVID-19 Questions

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

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  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.

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

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.

Last updated 12/15/2020

What companies are working on a 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.

Last updated 12/15/2020

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):

Last updated 12/15/2020

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. 

Last updated 12/15/2020

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.

Last updated 12/15/2020

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:

Last updated 12/15/2020

Does the anthrax vaccine protect against 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.

Last updated 12/15/2020

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.

Last updated 12/15/2020

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.

Last updated 12/15/2020

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.

Last updated 12/15/2020

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." 

Last updated 12/15/2020

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.

Last updated 12/15/2020

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

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.

Last updated 12/15/2020

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.

Last updated 12/15/2020

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.

Last updated 12/15/2020

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.

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

Reviewed by Paul A. Offit, MD on April 23, 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.