Questions and Answers about COVID-19 Vaccines

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 severely from 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 possibly 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, while we wait, we can work together using important public health practices to limit the illness, deaths, and societal damage SARS-CoV-2 seeks to sow. 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.
  • 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.

If we all work together to decrease the spread of this invisible enemy, we can control it, giving scientists and healthcare providers more time to understand it and develop treatments and vaccines.

As we wait for COVID-19 vaccines, many people have questions about this disease and the vaccines being developed to prevent it. In the sections that follow, you can find a compilation of some of the most common questions people are asking.

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

COVID-19 vaccines

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. No currently licensed vaccines use this approach.

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, September 23, 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.

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 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.

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

It is likely that COVID-19 vaccines could have different levels of effectiveness in various subgroups of people. Because the elderly generally do not respond as well to vaccines, one or more COVID-19 vaccines may not work well for them, which is concerning given their higher risk of severe disease. The large phase III studies may not include people over a certain age. But, the manufacturers have been encouraged to include older people, so that we have this type of information earlier in the process than may usually occur. We will have to wait and see what the data show to know which vaccine(s) work best in the older population.

If early vaccines are not as effective in elderly populations, it is likely that one or more manufacturers will explore alternative versions, such as higher dose versions, as was done for influenza vaccines. Another possibility would be to use a single protein from coronavirus (the spike protein) surrounded by two powerful adjuvants, similar to the shingles vaccine, Shingrix. This vaccine also works well in the elderly.

I have a health condition that prevents me from getting vaccines with live viruses. Do you know if the COVID-19 vaccine uses dead or live virus?

Right now, there is not a vaccine available, but several types of vaccines are being tested. None of the early vaccines being tested by Moderna, Pfizer, AstraZeneca, or Johnson & Johnson are live weakened versions (similar, for example, to the measles, mumps, rubella, or varicella 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?”

When vaccines are licensed, part of the information that will be provided will include who should or should not get each vaccine. At that time, we recommend talking with your healthcare provider regarding which vaccine will be the best one for you to get, given your medical history.

I heard that some COVID-19 vaccines are being made in fetal cells. Is this true?

Many scientists are working to design COVID-19 vaccines, including a few that could 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 some 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.

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

The number of doses of a COVID-19 vaccine that will be needed has not yet been determined. The coronavirus vaccines being studied are evaluating one or two doses. When giving two doses, they are usually given one or two months apart. We will need to wait for the results of the clinical trials to have more information about how many doses will be needed. 

Also, since several vaccines are likely to become available over time, it is possible that some vaccines will require one dose while others may require two doses. It is also possible that over time, additional doses of vaccine may be needed to provide continued protection. It will take ongoing evaluation over several months and years to understand how our immune systems respond to this virus and how vaccines that become available assist in that response.

How long will vaccine immunity last?

Since we do not yet know how long immunity after infection lasts, immunity following vaccination will also have to be determined. Likewise, immunity following vaccination will depend in part on which types of vaccines are licensed, what part of the immune system responds to the vaccine, and the level of immunity that is generated by the vaccine.

If you had the virus and recovered will you still be able or need to get the vaccine?

Right now, we do not know how long antibodies last after infection or whether they will protect against reinfection. So, while vaccine trials are being completed, it will be important for scientists to continue learning about COVID-19, particularly whether people who got sick with COVID-19 can be re-infected. The current vaccine trials will include immunizing people who have never been infected with SARS-CoV-2 as well as those who have been previously infected. We will soon know whether vaccination of those who have been previously infected affords more complete or longer lasting protection than those who were previously infected but haven’t been vaccinated.

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

If an individual is vaccinated and they are protected from infection, they will not transmit the virus to someone else. But, it is expected that COVID-19 vaccines may protect against severe infection, but not necessarily prevent mild or asymptomatic infection. If this is the case, a vaccinated person could still spread the virus if they are infected. This is why it is expected that even after a vaccine becomes available, people will need to use masks and practice social distancing measures for some time.

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

While it is likely that more than one COVID-19 vaccine will become available, we probably won’t have a good answer to this question until vaccines are actually licensed and we know more about them.

Three scenarios can occur if a person is 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.

Will a coronavirus vaccine need to be given annually?

When a vaccine is licensed, we will only have information about length of immunity for as long as we are from the trials. For example, if the first people in the study were vaccinated in July 2020 and the vaccine is licensed in December 2020, we will only have information about the immune response up to 5 months after vaccination. The vaccine manufacturer will likely continue to monitor vaccine recipients for several months or more, so that over time, we will continue to get a better picture of the durability of immunity. With this information, we will be better able to understand whether vaccines against COVID-19 will require annual dosing like influenza.

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. This specific immunity can be achieved in one of two ways — through illness or vaccination. Since illness could lead to severe disease or death, vaccination is a better alternative as long as safe and effective vaccines can be developed.

How long before a coronavirus vaccine takes effect?

Generally speaking, it takes a week or two for immunity to develop following vaccination, but the specific timeline for any coronavirus vaccine will depend to some extent on which type of vaccine is licensed. For example, a live, weakened vaccine requires time to reproduce in the body, whereas an inactivated vaccine is given at a dose that will generate immunity. On the other hand, because the live, weakened vaccine reproduces to generate immunity, it might provide a more robust immune response than an inactivated vaccine.

COVID-19 vaccine studies

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 do not have proven treatments, so treating anyone from a study who becomes ill would be further hindered by the limits of what we know about effective treatments.
  • 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.

Does the mutation of coronavirus affect the vaccine studies?

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 development of a vaccine. So far, the virus that causes COVID-19 does not appear to change very frequently. 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, recently identified changes have enabled the virus to spread more easily, but that change did not affect the way antibodies respond to the virus. Antibodies from people who had an earlier version of the virus are still able to protect against the newer version, so a vaccine would likely also still be effective.

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. Currently, phase III trials of the COVID-19 vaccine are designed to include about 20,000 people who will get vaccine and 10,000 people who will get a shot that doesn’t contain the vaccine (i.e., a placebo). Some companies, however, might do smaller phase III trials.
  • After a vaccine is licensed, scientists will continue to monitor its use in “post-licensure studies.” In this way, they will 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).”

How long does each phase of trial test 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 has been 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 has invested in some of the potential vaccine candidates to allow for building the manufacturing facilities and making vaccine doses before it is known whether the vaccine works. If the vaccine works and is safe, doses will be ready to be distributed shortly after the vaccine is approved for use, but if the vaccine does not work, the doses will need to be discarded.

You can find out more here:

What will be needed to license 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. They will need to provide data for review and information, so the FDA and other scientists can understand how the studies were designed, how many people were evaluated, and 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.

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.
  • Some studies are evaluating both viral shedding and protection against moderate or severe disease.

Is the coronavirus vaccine being studied in children or pregnant women?

As with most vaccines, studies will need to be conducted in children and in pregnant women, but these studies are often done after the vaccine has been shown to work and be safe in healthy adults. Given the current circumstances, the Food and Drug Administration (FDA) has encouraged vaccine manufacturers to consider including pregnant women in the current studies. Children will most likely be studied after one or more vaccines are approved. 

Could any of the vaccines currently in trial be approved for use in children without pediatric trials, or will these vaccines all need to undergo a separate clinical trial process before they can be given to children younger than 18 years of age?

COVID-19 vaccines should 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.

It is possible that trials in children would be smaller than the 30,000 person trials that are in process in adults, but enough children will still need to be tested to ensure that they develop immunity and that unforeseen side effects do not occur. Likewise, ongoing monitoring will need to occur in both adults and, eventually, children once vaccines are licensed to watch for infrequent side effects that are not detected until several hundred thousand or a few million doses are given.

If vaccine trials do not include people with autoimmune conditions, how will we know if they can be vaccinated?

The requirements related to who can participate in a vaccine trial vary based on the company running them, the disease they are seeking to protect against, and various types of autoimmune conditions. Often the first studies are the most restrictive, so that the data are not influenced by other conditions. Later scientists and healthcare providers will accumulate data for different sub-groups. In some cases, specific trials will be conducted, but often the information on healthy adults can inform what to expect regarding different conditions. Because often groups of people with a particular condition may be small, a formal clinical trial cannot be performed, but experience with similar vaccines and understanding of the implications of the disease on the immune system inform risk/benefit decision-making. Over time, as more people with the condition are vaccinated, data accumulates. Post-licensure monitoring systems, like the Vaccine Adverse Events Reporting System (VAERS) and the Vaccine Safety Datalink (VSD), provide opportunities for real-time monitoring of these sub-groups.

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. More than 15 of the vaccines have started being tested in people. The vaccine trials are being conducted by Moderna, Pfizer and BioNTech, The University of Oxford and Astra Zeneca, Inovio, Johnson & Johnson, Bharat BioTech, Clover Bio Pharmaceuticals, CanSino, SinoPharm, Sinovac BioTech, Imperial College London and Morningside, Anges and Osaka University, Curevac, Genexine, Gamaleya Research Institute, Vaxine, Medicago, and the University of Queensland, among others.  More vaccine candidates are likely to start clinical trials soon.

The vaccines furthest along in testing in the United States include those from Moderna, Pfizer and BioNTech, The University of Oxford and Astra Zeneca, and Johnson & Johnson.

COVID-19 vaccine availability

Is there a vaccine against COVID-19?

No. Currently, a vaccine against COVID-19 is not available, but several are in development.

Why isn’t there a coronavirus vaccine?

SARS-CoV-2, the virus that causes COVID-19, is a new virus. It did not exist before late 2019, so it will take some time for scientists and healthcare providers to learn about the virus and how to treat and prevent it.

An unprecedented amount of resources have been made available to develop a COVID-19 vaccine, and many scientists and labs are working on their development. Therefore, it is likely that one or more vaccines will become available more quickly than any vaccine that has ever been made. Most vaccine research and development programs take about 15 years. The coronavirus vaccine will likely be available in 1.5 years. With this said, the vaccine development process is being carefully monitored by governments and independent scientific committees to ensure that any vaccines made available were evaluated appropriately for safety and the findings made available for independent review.

When will there be a vaccine against COVID-19?

No one knows precisely when a COVID-19 vaccine will be available. While late 2020 or early 2021 have been suggested as target dates, it is important for people to understand what that projection means.

First, science keeps its own timeline, meaning that while a scientist may have a goal in mind, the research may or may not progress as planned. In science, we don’t know what we don’t know, so while it is important to have goals in mind, part of the scientific process is understanding that unanticipated issues may change the plan.

Second, even when a vaccine is finally licensed, that does not mean it will be immediately available for everyone to get it. Several important considerations are relevant:

Production — One of the ways that vaccine developers are hoping to shorten the timeline for a COVID-19 vaccine is that they are producing doses of vaccine while the vaccine is still being studied for safety and effectiveness. This means in some cases they will be producing vaccine as if it were licensed before they actually know if it will ever be approved for use. If the vaccine is approved, the companies and the population will win because they will have a stock of vaccine ready to ship as soon as they are allowed to do so. But, if the vaccine is not approved, they will need to discard all of the vaccine doses. By paying for mass production of vaccines prior to knowing whether they are effective in a phase III trial, the U.S. government has removed the risk for pharmaceutical companies if their vaccine is shown to be unsafe or ineffective, in which case all of the mass-produced vaccine would have to be discarded.

Distribution — Once a vaccine is approved, even with doses ready to go, the vaccine will need to be shipped to facilities where it will be administered.

  • First, it is important to realize that no company will have enough doses ready for the entire global population, so decisions will need to be made about which countries get how many doses. Public health experts agree that these decisions should be made based on where outbreaks are occurring because decreasing spread in any region of the world protects all regions of the world. To date, more than 170 countries have agreed to participate in a global cooperative, called the COVAX Initiative. The initiative is co-led by:
    • Coalition for Epidemic Preparedness Innovations (CEPI)
    • Gavi, the Vaccine Alliance
    • World Health Organization (WHO)

The candidate vaccines being supported offer participating countries access to the “largest and most diverse vaccine portfolio in the world.” The U.S. is not currently participating in this initiative.

  • Second, with limited doses available at the start, prioritization of different groups within a population will also likely be necessary. These decisions should be informed by risks of disease. For example, some experts have suggested that healthcare providers and essential workers should be prioritized, as well as sectors of the population at higher risk of suffering severe disease and death, such as those living in long-term care facilities and certain races and age groups that are experiencing more severe disease and death. In the U.S., the decisions regarding which groups would most benefit from early vaccines will likely be determined by the Centers for Disease Control and Prevention (CDC), although the National Academies of Sciences, Engineering, and Mathematics created a framework for the equitable allocation of COVID-19 vaccines, following a public comment period in early September 2020.

Supply chain — In addition to the vaccine, supplies needed for administering it must also be available in sufficient quantities. In some cases the need for supplies to vaccinate may compete with needs for treatment, such as personal protective equipment (PPE). In other cases, it may depend on how the vaccine is administered. For example, a vaccine given as a shot will require needles and syringes. Depending upon the route of injection, it may require a particular length of needle. Some needs can be anticipated while we wait for a vaccine, but others will depend upon the vaccine.

For these reasons, the discussions related to a vaccine timeline are more complex than may be realized from reports in the media.

I heard the U.S. has 2 million doses of COVID-19 vaccine ready to give to people. Is this true?

As described in the previous question, some companies may be making doses of vaccine in anticipation that the vaccine is found to be both safe and effective. But, what supplies they have and whether they are in a format to be distributed would be difficult to know. Further, the most important consideration at this time is not whether doses of a vaccine are ready, but rather how potential vaccines are being tested to ensure that they work and are safe. So that, when a vaccine is eventually licensed, we can be confident in our choice to use them.

Who will get the vaccine first?

Because a single vaccine manufacturer will not be able to quickly meet the global demand for vaccine, it will take time and, hopefully, more than one vaccine to immunize the large numbers of people who will need to be vaccinated. Therefore, who will get early doses of the coronavirus vaccine is an important topic that is now being discussed in the United States by the COVID19 Work Group of the Advisory Committee on Immunization Practices (ACIP). The National Academies of Sciences, Engineering, and Mathematics recently released a framework to offer guidance to the federal government. But, it is likely that these types of decisions will not be made until at least one vaccine is available.

Several factors will go into deciding who will get early doses of vaccine:

  • Vaccines might work differently in different groups. So, what we know about how well the vaccine works in different groups will be a factor. For example, if a vaccine does not work well in older people, even though they need the vaccine, it may be more effective to immunize younger people who could spread the disease to those individuals.
  • How safe the vaccine is and whether it is more or less safe in certain groups of people. For example, do certain groups of people have more side effects, while others do not?
  • Where are disease outbreaks occurring? While the goal is to eventually immunize most of the populations throughout the world, stopping outbreaks that could spread to other parts of a country or to other countries, helps everyone.
  • The number of doses available will also be a consideration.

Some groups being discussed for prioritization include healthcare providers, essential workers, people 65 years of age and older, people who live in long-term care facilities, and people with high-risk conditions, like heart disease, chronic lung disease, or who are pregnant. But, as described, it will be difficult to make decisions until additional details become available.

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

At this point, no one can really answer the question as to when everyone in the U.S. would be able to be vaccinated for a few reasons:

  • First, we do not know when the first vaccine will be licensed or how many doses will be available when it is.
  • Second, we do not know whether other vaccines will follow shortly thereafter and how many doses of those will be available when licensed. Additional vaccines would help speed up the timeline.
  • Third, in some cases vaccines may not be readily available for certain sub-groups of people based on how the phase III studies were completed. For example, currently, none of the phase III trials include children under the age of 18 years old. As a result, additional studies will need to be completed to ensure that a licensed vaccine is safe for that age group.
  • Further, if any of the vaccines are not effective in certain age groups, those people may not be recommended to get vaccinated with particular versions.
  • Finally, although a tiered system is being discussed, at this point, it has not been determined for sure who will be in the various tiers.

Additional factors related to level of disease, number of doses needed, and vaccine acceptance will also play into how initial doses are distributed.

Understandably, this is not an ideal answer, but it is meant to illustrate the uncertainties that remain at this point. As vaccines are licensed, we will have more information to better offer guidance related to when different groups of people should be able to get vaccinated.

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

Studies will have to be done to determine whether coronavirus vaccine is safe if given with other vaccines and that the two vaccines do not interfere with the immune response to each other. These are called concomitant use studies. It is possible that some of the later coronavirus vaccine trials will be tested with other vaccines, particularly the influenza vaccine, but that will depend on a variety of factors and would have to be approved as part of the clinical trial protocol.

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.

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 will be 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 fall. 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 overwhelmed.

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.”

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:

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.

How much will the coronavirus vaccine cost?

At this time, coronavirus vaccines are expected to be distributed for free. Insurance companies would likely have to cover the cost of administering the vaccine.

COVID-19 vaccine safety

How will we know if a COVID-19 vaccine is safe?

It will be important that any company producing a vaccine shares their data in a scientific forum, so that the part of the scientific process called peer review can be exercised. Peer review is an important part of science because it allows other scientists to critically review the methods, results and conclusions of a study, ensuring that the approach was sound and the conclusions, valid.

If the media is reporting on data, consumers need to evaluate those reports to determine whether the information was retrieved from the manufacturer through interviews or a press release or whether it was retrieved after being vetted through the peer-review process. You can find tips for evaluating information from both media reports and scientific studies, as well as websites, on this VEC Q&A sheet, titled “Evaluating Information: What You Should Know.”

In addition to evaluating how the study was designed (e.g., were there appropriate control groups? Was the study double-blinded? etc.), one of the most important components of COVID-19 vaccine studies that scientists will be interested in will be their size. Phase III vaccine studies typically include tens of thousands of participants. Although very rare side effects may not be discovered until a vaccine is given to hundreds of thousands of individuals, large phase III studies are likely to uncover any major safety concerns.

Finally, it will be important that any side effects found during clinical trials are made clear to those trying to decide whether or not to be vaccinated. 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 may be approved outside of the normal process, because of the emergency authorization 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.

What ingredients will be in a COVID-19 vaccine?

The ingredients that will be used in a COVID-19 vaccine will depend on the type of vaccine that is ultimately licensed. As vaccines are licensed, better answers will become available because that is part of the information that companies submit during the licensure process.

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.

Can mRNA vaccines change the DNA of a person?

Like with DNA vaccines, people also wonder whether mRNA vaccines can change a person’s DNA. Both DNA and mRNA vaccines cause cells to make viral proteins, such as, in this case, SARS-CoV-2 proteins. When the proteins are made, they are released from the cell and cells from the immune system recognize them as foreign and attack them, generating an immune response.

A simplified explanation of the way a cell makes proteins is that DNA produces mRNA which cells use as the blueprint to make proteins. So, a vaccine made from mRNA is one step closer to the intended outcome. 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. While RNA viruses have a gene to make a protein that allows for RNA to be converted to DNA (a process called reverse transcription), mRNA vaccines do not include this gene, so the mRNA would not be made into DNA that could change a person’s DNA.

Further, mRNA is quite unstable, so even if mRNA vaccines are found to be effective against COVID-19, distribution and storage will be important for maintaining vaccine effectiveness.

COVID-19 vaccine news

I heard that they are skipping steps to make a vaccine more quickly. Is that true?

Scientists are working feverishly to create a vaccine more quickly than has ever been done in the past. However, it is imperative that speed does not decrease safety. For this reason, the timeline can only be shortened by so much.

Some of the approaches that are being employed to shorten the timeline without sacrificing quality include:

  • Skipping phase I or combining 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 can look at data from a group of people as phase II is progressing to make these evaluations.
  • Manufacturing at risk — While completing the large phase III clinical trials, manufacturers can begin producing the vaccine, so that if it is shown to be safe and effective, they will 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 can be prepared, including:
    • Developing plans for how to distribute the first, limited quantities that will be 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, if vaccination is targeted to adults over 65 years of age, planning how to reach those people for vaccination, without unintentionally exposing them to a crowd in which the virus may be spread, will be important.

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 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 once COVID-19 vaccines become available.

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

Will COVID-19 vaccines contain a microchip?

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

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.

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.

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.

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.

COVID-19 video resources

This section of the page will house video resources and interviews related to COVID-19.
The Race to a COVID-19 Vaccine with Dr. Paul Offit
University of Pennsylvania, Perry World House, Sept. 1, 2020

Paul Offit’s Biggest Concern about COVID Vaccines
Medscape, Sept. 9, 2020

Making a COVID-19 Vaccine at Warp Speed
Vaccine Education Center Current Issues in Vaccines webinar, Sept. 23, 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.)

Reviewed by Paul A. Offit, MD on October 12, 2020

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.