Q&A on COVID-19 Vaccines


One COVID-19 vaccine is now authorized in the U.S. and more are likely to follow. In this story, we answer some common questions about the shots.

For more information about specific vaccines, we’ve created or will be creating individual pages for COVID-19 vaccines that are authorized or likely to be authorized.

The first vaccine to receive the Food and Drug Administration’s green light is Pfizer/BioNTech’s two-dose mRNA vaccine, which was authorized via an emergency use authorization, or EUA, on Dec. 11. (For more, please see “A Guide to Pfizer/BioNTech’s COVID-19 Vaccine.”)

Close behind is Moderna’s vaccine, which also uses an mRNA platform, and is widely expected to get the same nod shortly after the FDA advisory committee’s Dec. 17 meeting. The external panel voted 20-0, with one abstention, that the vaccine’s benefits outweigh the risks for use in people 18 years of age and older. Moderna announced on Nov. 30 that its product had a 94% efficacy in preventing symptomatic disease in its phase 3 trial.

Vaccine candidates from Johnson & Johnson (also known as Janssen), AstraZeneca and Novavax are in some form of phase 3 testing, while other potential shots are in earlier stages of clinical or preclinical testing.

  • When can I get a vaccine, and how is it being distributed?

Access to a vaccine will depend on where you live and whether you’re at high risk of exposure to the coronavirus or of developing a severe case of COVID-19 if infected.

Given the limited early supply, the first COVID-19 vaccines are slated primarily for health care workers and nursing home residents. The federal government is doling out doses to states and other jurisdictions based on population, and letting those local governments decide on the specifics of prioritization within their borders.

Although states have leeway to make alternate decisions, most are sticking to the guidance from the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices, which concluded on an interim basis that the first vaccines (phase 1a) should go to the nation’s 21 million health care personnel and 3 million residents of long-term care facilities.

Health care workers are not only at increased risk of getting COVID-19, but also are needed to keep hospitals running during the pandemic. Those in nursing homes and similar facilities have higher rates of death or severe COVID-19 than other Americans, due to their age, preexisting conditions and shared living conditions.

Other prioritized groups that are expected to follow include essential workers, those 65 years of age and older, and people with medical conditions that put them at high risk of severe COVID-19. Each of these groups is large — ACIP estimates there are some 87 million essential workers, 53 million seniors and more than 100 million people with high-risk medical conditions.

All of this means vaccine doses are unlikely to become available to the general public beyond those groups for at least several more months, if not longer. 

Officials with Operation Warp Speed, the U.S. government’s effort to fast-track vaccine development and manufacturing, said on Dec. 14 that between Pfizer/BioNTech and Moderna, they expect to have enough doses to vaccinate 20 million people by the end of the year and 100 million people by the end of March. That would cover everyone in phase 1a and a portion of those in the next phases.

Vaccine supplies should expand significantly in the spring, assuming other vaccine candidates come online. Moncef Slaoui, chief adviser of OWS, said that the first doses from Johnson & Johnson could be available in February and those from AstraZeneca could start in March.

According to Health and Human Services Secretary Alex Azar, the U.S. government has already signed contracts to purchase enough vaccines to allow any American who wants to get vaccinated to do so by the end of June 2021, although that assumes the various candidate vaccines are authorized and companies are able to deliver the promised doses. 

Other experts caution that these timelines may be optimistic and will be in flux, as it’s not unusual to run into manufacturing hiccups as vaccine production is ramped up.

“It’s really hard to mass produce vaccines,” Dr. Paul A. Offit, a vaccine expert at the Children’s Hospital of Philadelphia, told us, adding that the delicate lipid-wrapped mRNA vaccines have never been scaled up before. “Hopefully there won’t be glitches.”

  • How effective are the vaccines, and what do they protect against?

The details will be specific to each vaccine, but the Pfizer/BioNTech and Moderna vaccines are both very effective at preventing symptomatic disease.

According to the results of the phase 3 trials, the two vaccines had an efficacy of 94% or higher, which approximately means your risk of getting sick is cut by 94% or more if you are vaccinated. That’s a very good result — although it’s important to keep in mind that the effectiveness of the vaccines outside the controlled setting of a clinical trial is typically somewhat lower.

Data from the Moderna trial also demonstrate that the vaccine protects against severe COVID-19. The Pfizer/BioNTech vaccine likely does as well, although the trial accumulated fewer severe cases, limiting the conclusions that can be drawn on that point.

The clinical trials evaluated whether people developed symptoms, and subsequently tested positive for the coronavirus, or SARS-CoV-2. What is still unknown is whether these vaccines protect against infection with the coronavirus, and if not, whether they reduce or prevent viral transmission. The shots might only protect against disease, which could mean vaccinated people who are infected but not showing symptoms could still pass the virus on to others.

Alternatively, as National Institute of Allergy and Infectious Diseases Director Dr. Anthony Fauci explained in an interview, it’s possible for a vaccine to block transmission even if it doesn’t prevent infection.

“The level of immune response that protected you from clinically recognizable disease would be enough to lower the titer of the virus in your nasopharynx such that you would not be infective,” he said of that scenario. “So you could be infected, but not have enough virus in your nasopharynx to transmit it.”

  • If I get vaccinated, can I return to my normal activities without precautions?

No, at least not yet. Since no vaccine is 100% effective, not everyone will be protected from falling ill, so it’s important to continue to be vigilant about physical distancing, avoiding crowds, wearing masks and washing hands, especially when the virus is continuing to circulate at high levels.

That’s further compounded by the fact that it’s not known yet if inoculation prevents someone from becoming infected or becoming contagious.

In a Dec. 13 interview, National Institutes of Health Director Dr. Francis Collins called this an “urgent” question to answer, but said it will take several more months to know for the Pfizer/BioNTech vaccine.

“What that means is if you’ve had the vaccine,” he said, “you still need to wear the mask, you still need to think of yourself as potentially contagious, even though you are protected from getting sick at a very high percentage of certainty. Masks are still going to be part of our life. We need to recognize that and not step away or start to drop our guard.”

  • How long will a person be protected if vaccinated?

Scientists don’t know how long vaccination will last, but this is something that the clinical trials, which are continuing, will try to answer.

Dr. Peter Marks, the head of the FDA’s Center for Biologics Evaluation and Research, which is responsible for vaccines, told JAMA on Dec. 14 that based on the people who were immunized earliest in the trials, it appears there’s a duration of protection against disease of at least several months.

“It’s probably not just two months,” he said. “It’s probably at least probably on the order of four to six months. The question is, will it reach out to a year? Hopefully yes, but I think we’ll have those data in the not too distant future — and we’ll have real data, because of the people who are being followed on the trial.”

Offit anticipates the protection might last years, although he cautions that that’s just a guess.

“I think the thing that was most encouraging, at least looking at the Pfizer and Moderna data, is they induce T cell responses, which means there’s decent T cell memory,” he said, adding that that suggests there would also be decent B cell memory.

Those memory responses would mean that even if a person no longer has circulating antibodies, they’d still be able to mount a rapid response if they encountered the virus and could likely avoid falling ill.

It may turn out that people will need to receive an additional shot periodically to boost the immune system to extend the duration of protection. But Offit doesn’t think this would need to be so frequent as every year.  

  • What side effects should you expect if you get a COVID-19 vaccine?

Reports suggest that many of the coronavirus vaccines will be more unpleasant to get than a typical shot.

Trial data from Pfizer/BioNTech and Moderna show that many people experience pain at the site of injection, fatigue, joint or muscle pain, headache, chills or fever after receiving the jabs. These reactions are more likely after the second dose, given several weeks after the first, and more common and severe in younger people.

Of the two vaccines, Moderna’s vaccine may produce a stronger reaction, as more people reported some of these symptoms and to a greater degree than in the Pfizer trial, although it’s hard to compare the two directly. 

Offit said these reactions were not dangerous — and are actually good signs of the vaccine working — but some people might end up missing a day of work or two.

Harvard immunologist Barry Bloom said in a press call that the difference could come down to the different lipid formulations used in each vaccine or the fact that the Moderna vaccine includes more mRNA per dose than the Pfizer/BioNTech shot.

No serious safety concerns were reported in either trial. 

Since the rollout of the Pfizer/BioNTech vaccine, several individuals in Alaska and Britain have had serious allergic reactions following receipt of the shot, although all have now recovered. Some allergic reactions are to be expected with any vaccine, although these are typically very rare.

The FDA is monitoring the situation and recommends those who have had a serious allergic reaction to a previous dose of the Pfizer/BioNTech vaccine or one of its ingredients to skip the shot. 

The CDC is also investigating and has advised that anyone who has previously experienced anaphylaxis be monitored for a half hour after getting the shot. Everyone else should be monitored for 15 minutes; all administration sites will be set up to treat allergic reactions.

  • Did the speed of vaccine development compromise on safety?

No. As Fauci has explained, the unprecedented speed of the COVID-19 vaccines was due to multiple factors, including past investments in mRNA vaccines, and did not require skimping on safety.

“The speed of it is a reflection of the extraordinary scientific advances that have been made in platform technologies for vaccines. It was not at the expense of safety,” he said. “In addition, an enormous amount of money — hundreds of millions, if not billions of dollars — were put into the development and the production of vaccine doses, so that they would be ready to give to people as soon as the vaccine was shown to be safe and effective.”

As a technology, one of the boons of mRNA vaccines is their speed — in terms of design, a plausible candidate can be cooked up just knowing the genetic sequence of the virus and an idea of which protein to target.

In this case, scientists already knew from past experience with SARS and MERS, which are other diseases caused by coronaviruses, that the spike protein the virus uses to enter cells was likely the right one. And much of the work had already been done in determining how best to ferry the RNA into cells.

Although no mRNA vaccine has ever received FDA approval before, this type of vaccine has been studied for years, including in people in some early-phase clinical trials.

The testing of the vaccines was also sped up by consolidating some of the early testing stages. As Icahn School of Medicine at Mount Sinai virologist Florian Krammer has written in the journal Nature, the trials “were designed such that clinical phases are overlapping and trial starts are staggered, with initial phase I/II trials followed by rapid progression to phase III trials after interim analysis of the phase I/II data.”

Frequently, these steps are only completed sequentially, largely because companies don’t want to proceed with expensive trials until there’s a sign that the vaccine will work. But with the government taking on the financial risk in many cases, that pressure was removed.

“It is very important to point out that moving forward at financial risk is the main factor that has enabled the accelerated development of SARS-CoV-2 vaccine candidates,” Krammer wrote, “and no corners have been or should be cut in terms of safety evaluation.”

The phase 3 randomized controlled clinical trials, which each enrolled upwards of 30,000 people, were also hastened because of the severity of the coronavirus outbreak in the U.S. With half of people receiving a placebo and the other half getting the vaccine, how long a trial takes is dependent on how rapidly COVID-19 cases accumulate.

And of course, production capacity was sped along by starting manufacturing even before knowing whether the vaccines would be successful. Here, another plus for the mRNA vaccines is that their components are often less time-consuming to produce than traditional vaccines, which require production of protein or virus in cells or eggs.

  • Why are the vaccines being authorized on an emergency basis, and how is that different from full approval?

Given the threat of the ongoing pandemic, the FDA is expediting its review of COVID-19 vaccines, and both Pfizer/BioNTech and Moderna applied for EUAs rather than the standard full licensure, which is known as a biologics license application, or BLA.

An EUA typically is a less stringent standard — regulators must determine that the product “may be effective” and the “known and potential benefits outweigh the known and potential risks.” But knowing that a vaccine will go into millions of healthy people, the FDA set up special, more rigorous requirements for a COVID-19 EUA for vaccines that resemble the requirements for a BLA.

In particular, the FDA required “at least one well-designed Phase 3 clinical trial that demonstrates the vaccine’s safety and efficacy in a clear and compelling manner” and said it expected vaccine companies to continue to collect data to pursue full FDA-approval. The agency also wanted to see at least two months of follow-up data on half or more of the participants.

That’s less than the minimum of six months that’s usually needed for a BLA, but in terms of safety, there is little reason to think more time would uncover any concerns.

“When vaccines cause serious and occasionally fatal adverse events, they invariably occur within six weeks,” said Offit, who serves on the FDA’s advisory committee.

It’s important to be clear that no vaccine or medical product is 100% safe, and so while large phase 3 clinical trials of the first two candidates have not revealed any safety concerns, it’s possible rare adverse events could crop up as the vaccine is moved into millions of people.

“I think you have to be humble and be open-minded to the fact that there may be a serious side effect,” said Offit.

But, as he told JAMA, this is always true when deploying a new vaccine, which is why surveillance systems are in place — and any theoretical risk of a vaccine must be balanced against the risk of contracting SARS-CoV-2.

“The choice not to get a vaccine here is not a risk-free choice. It’s a choice to take a different risk,” he said. “The term safety in the medical world means that the benefits outweigh what are at this point theoretical risks.”

If there is a rare serious adverse event, Offit told us, the good news is that it will be detected rapidly and usually within the first several million doses.

  • How can I report a potential safety issue?

The CDC and FDA have assembled multiple surveillance systems to monitor the safety of COVID-19 vaccines as they are taken by more and more people. Several of these systems draw on participation from the public, and people are encouraged to use them.

The first is the previously existing Vaccine Adverse Event Reporting System. Experts will comb through the submissions to identify and follow-up on adverse reactions that might be due to the vaccine.

The CDC is also rolling out a new smartphone-based tool called v-safe for COVID-19 vaccines. If you register for the program, you will be asked via text message how you are feeling every day for a week after vaccination and less frequently after that. If your answers indicate a potential problem, the system will flag your responses and someone will contact you for more information.

  • How much will a COVID-19 vaccine cost?

For the duration of the pandemic, no one should have to pay anything for a COVID-19 vaccine or its administration.

Karyn Schwartz, a senior fellow with the Kaiser Family Foundation with expertise in health insurance, told FactCheck.org that the vaccines themselves are being provided by government free of charge and there will be no out-of-pocket costs for patients due to various changes to health insurance rules, such as through the Coronavirus Aid, Relief, and Economic Security, or CARES, Act, and the Families First Coronavirus Response Act. 

Vaccine providers are allowed to bill insurance companies for administering the vaccine, however, so Schwartz said people should not be alarmed if asked to provide their health insurance information.

“Insurers will be picking up some of the administration costs,” she said. “But it won’t be like so much else in health care where you think it’s covered by your insurance and then it’s not and you get a bill.”

At some point, the government will stop purchasing doses, and COVID-19 vaccines will likely become like other shots that are covered by insurance — and some of the protections in place will go away, especially if you are uninsured, Schwartz said.

Unless the law is changed, though, she added, COVID-19 vaccines for Medicare enrollees will always be covered under Part B with no cost-sharing.

  • Will I have a choice in the specific vaccine I receive?

No, at least not to start. While there are likely to be two or more vaccines available soon, supplies of each will still be limited for months, and it’s unlikely you will be able to choose which one you get.

But if doses become plentiful, Offit said that could change, although he estimated that might not happen until the end of 2021.

  • Could a COVID-19 vaccine become mandatory?

It’s possible that in the future, when COVID-19 vaccines are no longer in short supply, that states or certain workplaces might require individuals to be vaccinated. 

As legal and public health expert Joanne Rosen of Johns Hopkins University has explained, the legal precedent for states to make vaccinations compulsory goes back to a 1905 Supreme Court case, Jacobson v. Massachusetts, in which a man challenged an ordinance requiring all adults to be vaccinated against smallpox or to pay a $5 fine. The court sided with the state, finding that the smallpox inoculation requirement was a reasonable regulation to protect public health.

Employers are also allowed to require their workers to get a vaccine, but only if vaccination is reasonably related to a person’s job duties. That typically includes places such as hospitals or nursing homes, which often require their staff to get flu shots each year.

The federal government cannot issue a vaccine mandate, Rosen told us, although it can provide financial incentives to nudge states to enact mandates. 

She said she would not be surprised if some workplaces do introduce COVID-19 mandates, but was less confident that states would, at least in the shorter term.

“I don’t know if states will enact COVID-19 vaccine mandates or will opt, instead, to strongly encourage people to get vaccinated and roll out public education campaigns,” she said.

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