Your Questions About COVID-19 Booster Shots, Answered

Booster shots are recommended for everyone 5 and older. And people 50 and older are eligible for a second booster dose.

A healthcare worker prepares Pfizer-BioNTech Covid-19 vaccines for third doses at a senior living facility in Pennsylvania.
A healthcare worker prepares COVID-19 vaccines for third doses at a senior living facility in Pennsylvania.
Photo: Hannah Beier/Getty Images

Booster shots have been widely available for anyone 12 or older since early January, when the Food and Drug Administration expanded the authorization for booster doses of the Pfizer-BioNTech COVID-19 vaccine. Booster shots had become available to all adults in November 2021 and to older adolescents in December. In March, the FDA authorized an additional booster shot for some immunocompromised people as well as anyone 50 and up.

On May 17, the FDA expanded booster access further, to allow children ages 5 to 11 to get a booster dose of the Pfizer-BioNTech vaccine five months after receiving their second dose. Two days later, the Centers for Disease Control and Prevention recommended that this age group get boosters, making boosters recommended for everyone 5 and older. “The omicron wave has seen more kids getting sick with the disease and being hospitalized, and children may also experience longer-term effects, even following initially mild disease,” FDA Commissioner Robert M. Califf, MD, said in a statement.

“COVID-19 vaccines have proven to be the best and highly effective defense against COVID-19,” Janet Woodcock, MD, acting commissioner of the FDA, said in a November 2021 statement. Authorizing boosters “helps to provide continued protection against COVID-19, including the serious consequences that can occur, such as hospitalization and death.”

While the uptake of booster shots among Americans has been slow so far, officials have urged people at higher risk to get not just one booster dose, but two. “Current evidence suggests some waning of protection over time against serious outcomes from COVID-19 in older and immunocompromised individuals,” Peter Marks, MD, PhD, director of the FDA’s Center for Biologics Evaluation and Research, said in a March statement. “Based on an analysis of emerging data, a second booster dose of either the Pfizer-BioNTech or Moderna COVID-19 vaccine could help increase protection levels for these higher-risk individuals.”

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Before boosters were authorized, Pfizer-BioNTech and Moderna released results indicating that the protection offered by those vaccines against infection waned over time. But the data also showed that they still appeared to provide good protection against severe disease, hospitalization, and death. 

Boosters are safe and effective, and they can help protect individuals susceptible to severe disease, according to an FDA analysis of the evidence. Research indicates that even though the omicron variant can evade some of the protection against infection offered by vaccination, boosters significantly raise levels of protective antibodies against the variant, which rapidly became the predominant variant in the world after being first identified in fall 2021. People who have received a booster dose are less likely to be infected and far less likely to develop a severe case of the disease that could require hospitalization, according to studies published by the CDC and in the journals JAMA and The New England Journal of Medicine.

Still, booster protection wanes eventually, too, with some protection against infection and severe disease falling off three to six months after that dose. Early data from Israel suggests that when people 60 and older get a second booster, the extra protection against severe disease lasts at least six weeks, according to a study published in The New England Journal of Medicine on April 5. But boosted protection against infection overall appeared to wane after about four weeks, according to the study, even if protection against severe disease lasts longer.

With a potentially serious surge expected this coming fall and winter, vaccine manufacturers are planning to have a new round of boosters available in the fall, targeting some of the ways the virus has mutated since vaccines were first authorized.

Consumer Reports talked with experts and examined the data to better understand what we know about boosters, who should get them, and why they have sparked debate in the scientific community.

Who Is Eligible for a Booster Shot?

Anyone 5 or older who got a Pfizer-BioNTech or Moderna vaccine at least five months earlier or a Johnson & Johnson vaccine at least two months earlier is eligible and should get a booster, according to the CDC. As of June 22, 2022, about 105.1 million people in the U.S. had received booster shots.

On March 29, the FDA authorized a second booster dose with a Pfizer-BioNTech or Moderna vaccine at least four months after the initial booster dose for people 50 and older.

As of June 22, about 16.6 million people had received a second booster dose, the CDC. Whenever you are eligible for your first or second booster, you should get it as soon as you can, according to the agency.

Because the immune systems of many immunocompromised people don’t generate sufficient protection after the first two vaccine doses, researchers have determined that a third dose—not technically a booster—is beneficial for many of them. This applies to those who are on immunosuppressant drugs after an organ transplant, as well as people who have a similar level of immune system impairment. People 12 and older who are moderately or severely immunocompromised and got an mRNA vaccine (Moderna or Pfizer) are eligible for their third vaccine dose four weeks after their second shot and a booster shot five months after that (for a total of four shots).

On March 29, the FDA also authorized a second booster (a potential fifth shot) for similarly immunocompromised people 12 and older who received their initial booster at least four months earlier.

The booster recommendation for immunocompromised people who received the single-shot J&J vaccine is the same as for everyone else who got a J&J shot—two months after the initial dose.

What’s the Evidence That People Need Boosters?

While currently available vaccines—especially the mRNA vaccines made by Pfizer-BioNTech and Moderna—are highly effective, data shows that the protection they provide wanes over time. Boosters have been shown to restore that protection, and research indicates that a booster is particularly important for raising protection against the omicron variant.

In data that Pfizer and BioNTech submitted to the FDA, the companies cited a preliminary study by the healthcare company Kaiser Permanente, which found that the vaccine’s efficacy against infections with the delta variant declined from 93 percent a month after initial vaccination to 53 percent four or more months after vaccination. Efficacy against hospitalization remained at 93 percent. Evidence presented by Pfizer indicated particular concerns about immunity waning for older people.

On Sept. 15, 2021, Moderna released data showing that people who were immunized with its vaccine between December 2020 and March 2021 were about 36 percent less likely to develop a breakthrough infection than those who were immunized between July and October 2020. The company said this apparent decline in protection supported the use of a booster dose. But it also said the vaccine was still about 95 percent effective at preventing hospitalization with COVID-19. 

In its submission to the FDA requesting authorization for a booster dose, Johnson & Johnson said that while its vaccine remained highly effective against the most severe cases of COVID-19 (which resulted in hospitalization or death), its efficacy against moderate to severe COVID-19—which was lower than the mRNA vaccines from the start—had fallen over time, driven by reduced protection against variants of the coronavirus. During the FDA advisory committee meeting discussing J&J boosters, FDA and CDC experts stressed that the lower level of protection for people who had received only one J&J shot made a booster particularly important for this group.

Omicron significantly changed the booster calculus. According to one study published by the CDC, vaccines remained 76 percent effective against hospitalization more than six months after a second dose while delta was the predominant variant. Once omicron became the predominant variant, vaccine efficacy against hospitalization six months after a second dose fell to 57 percent. But two weeks after a booster dose, vaccine protection against hospitalization rose back to 90 percent.

In Pfizer and BioNTech’s request to authorize a fourth shot, the companies said that data from Kaiser Permanente Southern California showed that the protection an initial booster provided against infection and severe disease caused by omicron waned after three to six months.

Boosters may be especially important for kids ages 5 to 11 because for this group, the protection against infection with the omicron variant provided by two initial very small vaccine doses has been lower. “Since authorizing the vaccine for children down to 5 years of age in October 2021, emerging data suggest that vaccine effectiveness against COVID-19 wanes after the second dose of the vaccine in all authorized populations,” Peter Marks, MD, PhD, director of the FDA’s Center for Biologics Evaluation and Research, said in a statement. “The FDA has determined that the known and potential benefits of a single booster dose of the Pfizer-BioNTech COVID-19 Vaccine for children 5 through 11 years of age at least five months after completing a primary series outweigh its known and potential risks and that a booster dose can help provide continued protection against COVID-19 in this and older age groups.”

Do Boosters Improve Immunity?

Yes. Data published by the CDC and peer-reviewed research published in medical journals show that boosters significantly improve immunity, including against the delta and omicron variants.

According to a study published Oct. 7, 2021, in The New England Journal of Medicine, a booster shot for people in Israel who were 60 and older and fully vaccinated at least five months earlier significantly reduced the risk for any breakthrough infection or for severe disease. Another NEJM study from Israel, published Dec. 23, found that people who received a booster dose were approximately 90 percent less likely to die from COVID-19 than vaccinated people who had not received a booster. (Unvaccinated people are still far more likely to die from COVID-19 than people who have received two doses of an mRNA vaccine.)

CDC research indicates that boosters significantly lower the risk for hospitalization due to the delta or omicron variant. And a study published by CDC researchers in the journal JAMA shows that even though omicron is able to evade some of the protection against infection provided by vaccines, people who have received a booster are 66 percent less likely to test positive for omicron than people who received just two vaccine doses.

During an FDA advisory panel meeting April 6 discussing booster shots, the CDC presented data showing that while booster doses do indeed help prevent infection, their efficacy was highest against more severe cases and death. “The pattern here shows the clear benefit of a third dose during omicron,” said Lt. Cmdr. Ruth Link-Gelles, PhD, a CDC epidemiologist.

Still, research has increasingly shown that booster protection also wanes over time. According to a study released by the CDC on Feb. 11, two months after a booster vaccine efficacy against an emergency room or urgent care visit was 87 percent, and efficacy against hospitalization at that point was 91 percent. Four months after the booster, efficacy against an ER or urgent care visit fell to 66 percent, and efficacy against hospitalization fell to 78 percent.

Pfizer and BioNTech said that in people 60 and older, Israeli data shows that a second booster dose raises antibody levels to the peak seen with the initial booster. Rates of infection and rates of severe illness are significantly lower among those who receive a second booster, the companies say.

While protection against any infection starts to fall about a month after the fourth dose, protection against severe disease and death lasts at least six weeks—and could last longer, according to an April 6 study in The New England Journal of Medicine.

In the FDA’s authorization for a second booster dose, the agency said data showed that the second booster dose raised antibody levels against both delta and omicron variants of the coronavirus.

Are There Additional Risks From a Booster Shot?

The data presented during FDA and CDC meetings on boosters showed that side effects were similar to those after the second dose of an mRNA vaccine.

So far, data evaluated by the FDA indicates that the benefits of a booster dose outweigh the risk of myocarditis (heart inflammation), a rare complication some people experience after a dose of an mRNA vaccine that has generally resolved quickly. Rates of myocarditis after a booster are much lower than after a second vaccine dose, according to a CDC study released March 1.

In kids ages 5 to 11, commonly reported side effects after a booster dose are similar to those effects seen after an initial or second vaccine dose, including pain and redness at the injection site, fatigue, muscle or joint pain, and fever.

The FDA said no new risks were identified with a second booster dose based on several data sources, including an analysis of approximately 700,000 second booster doses given to people 18 and older in Israel.

Should You Get the Same Shot You Got the First Time?

That’s up to you. “Eligible individuals may choose which vaccine they receive as a booster dose,” the CDC statement said. “Some people may have a preference for the vaccine type that they originally received, and others may prefer to get a different booster.”

A study conducted by the National Institutes of Health indicates that a Moderna or Pfizer booster may raise antibody levels for J&J recipients far more than a J&J booster. This research is still preliminary; more is underway on which boosters might yield the strongest protection for recipients of J&J, Moderna, and Pfizer vaccines.

Keep in mind that Moderna’s booster shot is a different dose from the first shots—50 micrograms instead of 100. So if you’re getting a Moderna booster, you’ll want to make it clear to the provider that you don’t want one of the initial shots. Pfizer’s and Johnson & Johnson’s doses are unchanged for booster shots.

Where Can You Get a Booster Shot?

They’re being given at the same sites where coronavirus vaccines are available, including hospitals, pharmacies, doctors’ offices, and clinics. You don’t have to get a booster where you received your initial vaccination, but remember to take your vaccine card with you. Check with your state health department, or search Vaccines.gov to find a location near you.

Are the Booster Formulas Being Changed to Match Emerging Variants?

Yes. The booster vaccine doses that are being given so far are the same formula as the initial vaccine doses. But vaccine manufacturers have been studying booster formulas that use omicron or its subvariants, sometimes combined with the original strain of the virus that vaccines currently target.

At an FDA advisory panel meeting on June 28, the panel recommended that vaccine manufacturers should include components in booster vaccines that target the variants of the omicron strain of the coronavirus. So far, vaccine manufacturers have been working on booster formulas that target the first omicron strain. Both Moderna and Pfizer/BioNTech have presented some data showing that these formulas appear to do a better job targeting omicron. But agency representatives and advisory panel members indicated that manufacturers should target the omicron subvariants that are now the most common forms of the coronavirus in the U.S.

Pfizer said it could have vaccines with a new formula ready in early October; and Moderna said it could have updated vaccines ready by the end of October or early November. A Novavax representative at that meeting said the company could have updated vaccines ready by the fourth quarter of this year, but also noted that data indicates that the Novavax vaccines’ current formula—which has not yet received emergency authorization—does a good job targeting omicron subvariants.

It’s not yet clear that everyone will need a booster in the fall, but it’s likely that one will at least be suggested for older adults.

Will We Need Boosters Forever?

Down the road it’s possible that we may need a regular booster against the coronavirus as we do against the flu, says Joshua Barocas, MD, an associate professor at the University of Colorado School of Medicine who specializes in infectious disease.

But whether that’s the case depends on how well we control the ongoing pandemic, says Anna Durbin, MD, director of the Center for Immunization Research and a professor in the department of international health at the Johns Hopkins Bloomberg School of Public Health. The best way to ensure that we don’t need them soon or regularly is to stop the disease from spreading, and the best way to do that is to vaccinate the unvaccinated, both in the U.S. and around the world. The more unvaccinated people there are, the more chances there are for new variants to emerge.


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).