Your Questions About Coronavirus Vaccines, Answered

In the battle against COVID-19, more than half of American adults are fully vaccinated

Two vaccine vials Photo: Getty Images

In a remarkably short period of time—less than one year—scientists managed to design, create, and test several potential vaccines for SARS-CoV-2, the virus that causes COVID-19.

Today, more than half of American adults are fully vaccinated.

The Food and Drug Administration issued the first two emergency use authorizations for coronavirus vaccines in December, with an additional vaccine authorized in February. The first two were two-shot regimens, developed by Pfizer/BioNTech and Moderna, using similar technology. The third, which provides protection after just one shot, was developed by Johnson & Johnson.

In July the FDA added a warning (PDF) to the label of the Johnson & Johnson vaccine. It says that reports "suggest an increased risk of Guillain-Barré syndrome during the 42 days following vaccination." The syndrome is a neurological disorder that in severe cases can cause paralysis, though most people fully recover.

The warning came after about 100 preliminary reports of Guillain-Barré syndrome were detected after 12.8 million doses of the Johnson & Johnson vaccine had been administered. In a statement, the Centers for Disease Control and Prevention emphasized that "the risk of severe adverse events after COVID-19 vaccination remains rare."

As of July 13, at least 387 million vaccine doses had been distributed in the U.S. At least 184 million people have received at least one dose, and more than 159 million people are now fully vaccinated, according to the CDC.

In a May Consumer Reports nationally representative survey of 2,079 U.S. adults (PDF), 67 percent of Americans said they had already received or were very likely to get a vaccine. This percentage was the same as it was in April, and up from 47 percent in January.

For those trying to understand all the vaccine news and how it affects their lives, a number of questions remain. Consumer Reports has reviewed government guidance and consulted with experts to answer some of the most common questions. (Don’t see your question here? Send it to us at and we may answer it in an update to this article.)

Who Is Eligible to Be Vaccinated?

As of May 12, anyone in the U.S. who is 12 or older is eligible to be vaccinated.

What Does It Mean for the FDA to Provide Emergency Use Authorization?

Because of the public health crisis caused by the ongoing pandemic, the FDA is empowered to provide expedited permission to distribute a vaccine to certain populations (which could be a narrow group, such as just healthcare workers, or a much broader group, such as all adults) before fully approving a vaccine, provided the vaccine meets certain standards for safety and efficacy. This would be an emergency use authorization, designed to more quickly and easily enable use of a vaccine, according to the agency.

After the emergency is over, vaccines would need full approval for continued use.

How Is the Vaccine Being Distributed?

The federal government has a centralized system to order, distribute, and track vaccines, according to the CDC. Vaccines are ordered through the CDC.

More on COVID-19

States, however, have flexibility in how they distribute vaccines, according to Kathleen Neuzil, M.D., a professor of vaccinology and director of the Center for Vaccine Development and Global Health at the University of Maryland in Baltimore. Because of that, there is some variation in the ways states distribute vaccines to priority populations, she says.

Initially, the rollout was slower than hoped. But vaccines are now widely available, and distribution efforts are focused on reaching people who have not yet been vaccinated.

Where Can I Get a Vaccine?

Vaccines are being distributed at a wide variety of locations, including hospitals, long-term-care facilities, mobile and temporary clinics, doctors’ offices, and pharmacies, according to the CDC.

Your local government or health department should have a vaccine provider list or search tool to find locations, and you can also check VaccineFinder, which includes limited data on pharmacies that are distributing COVID-19 vaccines.

Are the Coronavirus Vaccines Free?

Yes. The U.S. government will pay for vaccines given to people living in the U.S., according to the CDC.

Providers may charge a fee for administering the vaccine, but the government has mandated that insurers (or the government, in the case of uninsured individuals) cover this fee, so people should not have any out-of-pocket expenses associated with vaccination.

How Long Does Protection Take to Kick In?

The Moderna and Pfizer-BioNTech vaccines require two doses—an initial shot and a booster, usually several weeks later. Generally with a two-dose vaccine, it takes about two weeks from the second dose for a vaccine’s protection to fully kick in, according to Natalie Dean, Ph.D., an assistant professor of biostatistics specializing in infectious disease and vaccine development at the University of Florida in Gainesville.

Though both doses are necessary, the FDA’s analysis of the Pfizer-BioNTech vaccine indicates that people appear to be somewhat less likely to get COVID-19 within two weeks of receiving the first dose. It’s unclear how long protection from that first dose may last. And the second dose is still required for full protection, to ensure a more durable immune response.

The J&J vaccine requires only one dose. Protection starts to kick in two weeks after vaccination and grows stronger over the next two weeks, according to the company.

How Long Will Protection Last?

It will take time and more research before we know how long vaccine-provided immunity lasts, according to the CDC.

On April 1, Pfizer and BioNTech announced that they now had enough follow-up data from clinical trials to say that their vaccine provided protection for at least six months. These results have not yet been confirmed by the FDA or other regulators.

The early evidence scientists have on how long natural immunity lasts after an infection with SARS-CoV-2 has been mixed. But scientists hope immunity from a vaccine is more durable. If it turns out that vaccine-induced immunity wanes after time, occasional booster shots may be needed, experts say.

If I Had COVID-19, or Think I Did, Should I Still Get Vaccinated?

Yes. The CDC says that because reinfection is possible (though rare, and unlikely in the first few months after a first infection), it’s recommended that people who have recovered from COVID-19 still get vaccinated.

At least some of the vaccine trials have included people who had recovered from COVID-19, according to Neuzil, the vaccinology professor at the University of Maryland, and it appeared to be safe for these people to get the vaccine.

Even if recovered patients have some natural immunity, the vaccine could provide some longer-term benefit, she says. The immune system’s natural response to a SARS-CoV-2 infection is varied, and in some cases protection might not last very long.

So far, the evidence suggests that the immune system boost from vaccines is much stronger and thus potentially longer-lasting than the natural immune system response, according to Andrew Pekosz, Ph.D., a virologist, professor, and vice chair of the department of molecular microbiology and immunology at the Johns Hopkins Bloomberg School of Public Health.

Can We Really Know Yet If a Vaccine Is Safe?

Even before the vaccines were given emergency use authorization, the FDA reviewed months of safety data on tens of thousands of participants in vaccine trials. Since then, regulators have tracked people who received a vaccine in the real world, because it’s possible that very rare side effects might emerge once millions of people receive a shot.

In the U.S., more than half of adults are now fully vaccinated, and even more have received at least one dose. With more than 300 million doses of vaccine administered and an intense safety monitoring program that’s able to track even extremely rare side effects, researchers have been able to track vaccinated people for months, and are confident that the COVID-19 vaccines currently authorized for use by the FDA are safe.

For the vast majority of people, side effects have been similar to those from other vaccines, like the shingles vaccine, though they have been more common and severe than they are with the typical flu shot. These side effects include fever, headaches, feeling run-down, and soreness in the arm. These are more common after the second shot than the first, and generally go away within a few days.

A few rare side effects have been detected, now that millions of vaccine doses have been administered.

After receiving the J&J vaccine, a very small number of people—primarily women younger than 50—have developed a type of rare but serious blood clot. In women between 18 and 49, there have been about 7 cases per million vaccinations, and the FDA and CDC still recommend this vaccine. Similar rare blood clots have been observed with the Astrazeneca vaccine in Europe.

In July, the CDC also announced that the agency had detected preliminary reports of about 100 cases of Guillain-Barré syndrome, a neurological disorder, among 12.8 million people who received the J&J vaccine. Most were men, many of them 50 and older.

After receiving either the Moderna or Pfizer-BioNTech vaccines, a small number of people have had a severe allergic reaction, called anaphylaxis, which can occur after any type of vaccination. These have occurred in about two to five people per million vaccinated, and while serious, they are treatable—this is why people are asked to stick around for 15 to 30 minutes after getting a shot (for more, see the question below).

The CDC is currently investigating higher than normal rates of suspected myocarditis (heart inflammation) in adolescents and young adults who have received the Pfizer or Moderna vaccines. These incidents are rare, and in 81 percent of suspected cases with a known outcome, patients have fully recovered. The CDC, the American Heart Association, and the American Academy of Pediatrics continue to recommend that anyone 12 or older get vaccinated.

Any longer-term side effect is extremely unlikely, according to the CDC. Typically, any vaccine side effects would emerge during these first two months after immunization, says C. Buddy Creech, M.D., director of the Vanderbilt Vaccine Research Program and a principal investigator on coronavirus vaccine efforts by Moderna and Johnson & Johnson.

Plus, he adds, it’s difficult to clearly link any adverse health events that occur after two months with a vaccination. But regulators will continue to monitor vaccine trial participants for two years to see how long immunity lasts and note any adverse events.

What Should I Know About Reports of Allergic Reactions to the Vaccine?

Initial reports of several severe but treatable potentially life-threatening allergic reactions called anaphylaxis raised concern about whether the vaccines would be safe for people with severe allergies.

There were 71 cases of anaphylaxis reported after the first 18 million vaccine doses were administered in the U.S., according to Jay Butler, deputy director for infectious diseases at the CDC. That works out to 2.8 cases of anaphylaxis per 1 million people vaccinated with the Moderna vaccine and 5 cases per 1 million doses of the Pfizer-BioNTech vaccine, with no reported deaths linked to anaphylaxis. The risks of getting COVID-19 are much worse, according to Butler—about 16,500 people per 1 million diagnosed with COVID-19 will die.

Now, the only people being told to avoid the vaccine are those allergic to vaccine ingredients such as polyethylene glycol or the related substance polysorbate.

Guidelines for the administration of both vaccines specify that facilities providing them should be prepared to manage severe allergic reactions.

The authors of a research review evaluating cases of anaphylaxis concurred with FDA and CDC guidance on vaccine administration. To minimize risk while maximizing the number of people vaccinated, they suggest that vaccine administrators ask patients about allergy history. People who report being allergic to a vaccine component should be given a skin test and should not receive the vaccine if that test is positive.

If patients report a history of severe allergies to food, medication, or other vaccines or injectable medications, the authors write that the vaccine can still be given, and that those vaccine recipients should be observed for 30 minutes after getting their vaccine dose (instead of the standard 15 minutes).

How Many People Need to Be Vaccinated for Normal Life to Resume?

Scientists don’t yet know, according to the CDC. Once enough people have some immunity, either because of previous infection or because of vaccination, the virus will have a hard time spreading through the community. Once that community protection exists, it may be possible to resume what we thought of as “normal” pre-pandemic life.

More research needs to be done before scientists can say exactly how many people need to be vaccinated. Researchers have hoped we might reach community-level protection when around 70 to 75 percent of people are vaccinated, according to Butler at the CDC. But more contagious variants of the virus could cause that number to rise to 80 or 85 percent, he says.

How Many Vaccine Doses Will the U.S. Need?

All but one of the COVID-19 vaccines that are in or have completed Phase 3 clinical trials in the U.S. require two shots to be effective, according to the CDC. (For more on the stages of vaccine trials, see our article on vaccine development.) In most cases, that means 100 million doses of a vaccine will be enough for 50 million people. There are about 250 million adults in the U.S., so we are likely to need 500 million doses to vaccinate everyone 18 and up—fewer once we factor in effective one-dose vaccines. (The vaccines are still being tested in children.)

The U.S. has announced purchases of enough vaccine doses for at least 300 million people, though not all have been distributed. That includes 200 million doses each of the Pfizer-BioNTech and Moderna vaccines, enough to vaccinate 200 million people in total. The U.S. has also purchased at least 200 million more vaccine doses, including at least 100 million doses of the one-shot J&J vaccine.

The CDC has said that people who don’t know if they received the Pfizer-BioNTech or Moderna dose the first time should still receive a second dose of whichever vaccine is available. The agency has also said that while people should get their second dose as close to the three- or four-week window as possible, getting it a little later is acceptable if that is necessary.

What Do the Efficacy Numbers Really Mean?

Pfizer-BioNTech and Moderna, manufacturers of the first two vaccines authorized by the FDA, reported that their vaccines appeared to be about 95 percent effective at preventing people from developing symptoms of COVID-19 in clinical trials.

In vaccine trials, roughly an equal number of participants receive the real vaccine or a placebo. Pfizer and BioNTech calculated that their vaccine was about 95 percent effective, for example, after observing that 172 out of the 181 COVID-19 cases that occurred in trial participants were in the placebo group—demonstrating that people who received the vaccine appear to be generally well-protected.

While other vaccines might not appear to be quite as effective overall, they may still be equally effective at preventing severe disease that requires hospitalization and puts people at risk for death.

The J&J vaccine, for example, appeared to be 66 percent effective overall at preventing moderate to severe COVID-19—72 percent effective in the U.S., 61 percent effective in Latin America, and 64 percent effective in South Africa. In South Africa, a virus variant that seems to be able to evade some vaccine-induced immunity is the predominant variant. Another variant was the predominant one in Brazil, where J&J conducted most Latin American testing.

But the J&J vaccine was 86 percent effective at preventing severe or critical disease overall 28 days after vaccination in the U.S., with similar efficacy against severe or critical disease in South Africa and Latin America. None of the more than 20,000 vaccinated people in the J&J trial died from COVID-19, and there were no COVID-19 cases requiring hospitalization for people in that trial who had been vaccinated for at least 28 days.

On March 25, AstraZeneca reported that clinical trials had shown its vaccine to be 76 percent effective against symptoms of COVID-19, with slightly better efficacy in adults 65 and older and even greater protection against severe disease and hospitalization. And on June 14, Novavax reported that clinical trials had shown its vaccine to be 90 percent effective overall, and 100 percent effective against moderate to severe disease. Still, all data on safety and efficacy will need to be reviewed by the FDA before the agency decides whether to authorize the use of that vaccine in the U.S.

Studies suggest that the degree of effectiveness in clinical trials is consistent with effectiveness in a real-world setting, according to the CDC. In a study published on May 14, CDC researchers found that being fully vaccinated (two doses) with either the Moderna or Pfizer-BioNTech vaccine was 94 percent effective in preventing symptomatic infection. (The study subjects were healthcare workers in 25 states, who were vaccinated between January and March.) An earlier CDC study showed that the Moderna and Pfizer vaccines appeared to be 90 percent effective in reducing the risk of infections in real-world settings.

And under real-world conditions in Israel, which has vaccinated one of the largest shares of its population of any country, an organization that provides medical care to over one-quarter of Israelis has reported that the Pfizer-BioNTech vaccine maintained that 95 percent effectiveness, according to Reuters.

Still, while manufacturers have done their best to test vaccines in a variety of populations, including people of different ages and races, and with different medical conditions, it’s possible that vaccines will turn out to be more or less effective in certain populations, according to Paul Offit, M.D., an attending physician in the division of infectious diseases at Children’s Hospital of Philadelphia and director of the hospital’s Vaccine Education Center. Offit is also a member of the FDA advisory panel.

Is It Unexpected That Some Vaccines Report 95 Percent Efficacy?

Before data from trials of these vaccines started to come in, researchers were hoping to see that the vaccines were 70 or 75 percent effective, according to Offit. FDA guidelines required the vaccines to be at least 50 percent effective to be considered for authorization.

Seeing that the Pfizer-BioNTech and Moderna vaccines were significantly more effective than that was “extraordinary,” Neuzil says. That indicates that it will be possible to have a significant impact on this pandemic and that some of the new vaccine technologies that were used during the development of these vaccines may come in handy for other viral outbreaks in the future.

It’s possible that “we enter into a golden age of vaccinology by having these types of new technologies,” says Creech at the Vanderbilt Vaccine Research Program.

Even vaccines that are less effective overall are still quite useful, especially if they can prevent severe disease. “In the event you have the choice to be vaccinated, I’d encourage you to take the vaccine that is given,” John Brooks, chief medical officer for the CDC’s COVID-19 response, said Jan. 29 during an IDSA call.

Why Are There So Many Different Kinds of Vaccines?

Many scientists and pharmaceutical companies started working on this problem at the same time, using as many different approaches as they could think of.

The first coronavirus vaccines to be authorized, those created by Moderna and Pfizer-BioNTech, relied on new technologies that had never been used in an approved vaccine before, according to Dean at the University of Florida. Usually, the barrier for trying to develop a new vaccine is cost, says Paul Duprex, Ph.D., a professor of microbiology and molecular genetics, and director of the Center for Vaccine Research at the University of Pittsburgh. But in this case, the federal government decided to step in to cover the financial risk.

Many of the new technologies used in the first batch of vaccines were designed for emergencies, Dean says, leading to fast development. It was important to try a variety of approaches, according to Neuzil, because there was no certainty that any one approach would work out. But the first vaccines that were authorized and others that are furthest along in the pipeline have at least one thing in common: They target the specific protein (known as the spike protein) that SARS-CoV-2 uses to infect cells.

The Moderna and Pfizer-BioNTech vaccines also use the same technology, called mRNA (more on that below). Given all these similarities, it’s reassuring to see that both have similar efficacy, Neuzil says.

How Are These Vaccines Made, and What Technology Do They Use?

The Pfizer-BioNTech and Moderna vaccines rely on technology known as messenger RNA, or mRNA.

To make an mRNA vaccine, researchers insert a bit of the genetic code from the virus into a lipid coating that can be injected into the body. Our cells use that code to create a harmless piece of the protein that SARS-CoV-2 uses to infect cells—without the dangerous parts of the virus. This teaches our immune system to recognize and respond to that protein, so the immune system is then able to fight off an infection from the real virus.

The mRNA can’t affect a person’s own genetic makeup—it breaks down after passing on the instructions used by our immune system.

The advantage of this technology, according to Neuzil, is that it was very fast to create a vaccine once scientists had identified the genetic sequence for the SARS-CoV-2 virus. Though these are the first mRNA vaccines that have been authorized for use, scientists have studied and conducted trials with mRNA vaccines for decades, according to the CDC. What we’ve seen about safety and efficacy of these vaccines is very encouraging, according to Matthew Zahn, M.D., medical director of the division of epidemiology and assessment for the Orange County Health Care Agency in California, speaking at a Feb. 18 briefing organized by the Infectious Diseases Society of America.

The J&J vaccine and several others, including AstraZeneca’s, use a different technology known as a viral vector. These vaccines use a harmless virus (not the one that causes COVID-19) to deliver instructions to make a part of a protein made by the virus that causes COVID-19. As with the mRNA vaccines, this teaches our immune system to respond to this protein, making it ready to fight off the real virus.

Novavax's vaccine is protein-based; it uses harmless proteins created from the virus that causes COVID-19 to teach the immune system to recognize a real infection. That's similar to the technology used in certain flu and HPV vaccines.

How Might Variants Affect the Vaccine?

As the virus that causes COVID-19 has spread around the globe, it has continued to mutate, as all viruses do. A number of variants—versions of the virus with specific sets of mutations—have emerged, and in many cases, become the dominant version of the virus in parts of the world.

Vaccines teach our immune system to respond to a virus by recognizing some key sign of it. Mutations that affect the parts of the virus the immune system recognizes can thwart a vaccine’s effectiveness.

Most of the vaccines currently in use or development target a particular protein—the spike protein—that the coronavirus uses to infect people. So mutations of that protein could potentially make a vaccine less effective, says Poland at the Vaccine Research Group at the Mayo Clinic.

But while the vaccines don’t seem to generate quite the same level of antibodies in response to some newer variants, that reduced activity has not been significant enough to blunt the vaccines' protection.

“So far, the vaccines we currently use here in the U.S. are effective in protecting against the variants,” says Tina Tan, M.D., a pediatric infectious disease specialist and professor of pediatrics at Northwestern University.

The Pfizer vaccine is still approximately 95 percent effective against the variant now known as the Alpha variant, which was first described in the U.K. and is now the dominant strain of the virus in the U.S., according to a May study in The Lancet, which looked at real-world effectiveness of that vaccine in Israel. And the full two doses of that vaccine are still approximately 88 percent effective against the newer Delta variant, though one dose is only 36 percent effective, according to data from Public Health England.

While it’s not yet clear whether we’ll eventually need to get booster vaccines, “the booster vaccines that all the companies are working on will include coverage for the variants that have so far emerged,” Tan says.

Will I Be Able to Choose Which Vaccine I Want?

As more vaccines become available—and if we learn that certain vaccines work better or cause fewer side effects for certain population groups—one vaccine might be recommended over another, as is the case now with flu vaccines.

It’s now possible to use the website to search for a specific vaccine. As appointments have become easier to come by, people seeking a particular vaccine due to a doctor's recommendation or simply personal preference may be able to find it.

When Will Children Be Able to Get Vaccinated?

Adolescents age 12 and up are currently eligible to receive the Pfizer vaccine. The FDA is expected to authorize additional vaccines for adolescents soon.

It's not certain, but children under age 12 may be eligible for the vaccine perhaps as early the fall. That’s according to a May 4 Pfizer earnings call, in which the company described plans to seek FDA authorization for use of its vaccine in children ages 2 to 11 in September. Pfizer also said it hoped to get authorization for the vaccine in infants in November.

Is the Vaccine Safe for Pregnant People?

Trials involving pregnant people are underway, according to the CDC. Animal tests revealed no pregnancy-related safety concerns with the Moderna, Pfizer-BioNTech, and J&J vaccines.

Already, guidance from the Advisory Committee on Immunization Practices permits individual pregnant people to choose to get the vaccine if they are part of a group that’s currently eligible to be vaccinated.

More than 10,000 already have without raising any red flags about safety so far, according to Anthony Fauci, M.D., director of the National Institute of Allergy and Infectious Diseases. And recent data indicates that the vaccines work for pregnant people: For a study published March 25 by the American Journal of Obstetrics and Gynecology, researchers followed 84 pregnant, 31 lactating, and 16 non-pregnant vaccine recipients. The researchers found that antibodies generated by vaccines in pregnant and lactating recipients were equivalent to the antibodies in those in the non-pregnant group and that these antibodies could be passed on to children through the placenta or breast milk. This indicates that the vaccines not only should help protect pregnant and lactating people but also may provide some protection to their children.

The CDC says that pregnant people may choose to get vaccinated with any of the currently available vaccines.

Can Vaccinated People Still Spread the Virus?

Yes, but research so far suggests they are much less likely to do so.

A study on real-world effectiveness released by the CDC on March 29 found that the Moderna and Pfizer-BioNTech vaccines were just as good at preventing asymptomatic infections as they were at stopping symptomatic ones.

Data released in February by the University of Oxford and AstraZeneca showed that vaccines may reduce overall transmission of the virus by about two-thirds. That could indicate that vaccinated people are significantly less likely to spread the virus, though it’s still possible for them to do so. Early data from Israel indicates that people who have received the Pfizer-BioNTech vaccine seem to have a lower viral load when they are infected, meaning they’d be less likely to infect others.

But while it’s likely that other vaccines might show some similar reduction in transmission, scientists don’t yet have the data to say for sure, according to Joshua Barocas, M.D., an assistant professor of medicine at the Boston University School of Medicine, speaking at an IDSA press call Feb. 3.

The CDC recently updated guidance to say that people who are fully vaccinated—meaning it has been at least two weeks since their last required dose—no longer need to quarantine if they are exposed to someone with confirmed or suspected COVID-19, as long as it has not been more than three months since the last vaccine dose.

After I Get a Vaccine, What Can and Can't I Do?

According to the latest CDC guidance released May 13, fully vaccinated people can safely stop wearing masks in most situations, indoors and outdoors. Vaccinated people with an underlying health condition or who take immune-system-weakening medications should talk with their doctors about what’s safe.

However, everyone should continue to wear masks in planes, trains, buses, and other forms of public transportation, as well as inside airline terminals, train stations, and other transit hubs. You should also still wear a mask in doctor’s offices, hospitals, and other healthcare settings.

The agency said, too, that states, municipalities, and businesses can still set their own rules, which supersede the CDC guidelines.

And while celebrating getting your vaccine dose is fine, the Better Business Bureau recommends not sharing a picture of your vaccination card on social media. Doing so could reveal your personal information and may allow scammers to create and sell counterfeit cards.

Will a Vaccine End COVID-19?

Researchers hope that vaccination campaigns will be sufficient to end the pandemic, Neuzil says, once there is sufficient vaccine supply and enough people get vaccinated. However, Offit, at the Vaccine Education Center, cautions that the whole world will need to have access to these vaccines for the disease threat to be fully eliminated. If the disease is still spreading somewhere, it could always reemerge, especially if people’s immunity wanes.

Editor’s Note: This article is updated frequently to include the latest developments. It was originally published Dec. 10, 2020.

Head shot image of CRO Health editor Kevin Loria

Kevin Loria

I'm a science journalist who writes about health for Consumer Reports. I'm interested in finding the ways that people can transform their health for the better and in calling out the systems, companies, and policies that expose patients to unnecessary harm. As a dad, I spend most of my free time trying to keep up with a toddler, but I also enjoy exploring the outdoors whenever possible. Follow me on Twitter (@kevloria).