Your Questions About COVID-19 Booster Shots, Answered

·11 min read

Boosters are now recommended for everyone 12 and up

A healthcare worker prepares COVID-19 vaccines for third doses at a senior living facility in Pennsylvania.

By Kevin Loria

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.

The expanded recommendations came just as the highly contagious omicron variant began causing the largest surge yet in COVID-19 cases.

Getting a booster dose “will provide optimized protection against COVID-19 and the omicron variant,” Rochelle Walensky, MD, director of the Centers for Disease Control and Prevention, said in a statement. “It is critical that we protect our children and teens from COVID-19 infection and the complications of severe disease.”

“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.”

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.

Data show that boosters are safe and effective and that 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 the fall of 2021. People who have received a booster dose are less likely to be infected and far less likely to develop severe 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. On March 15, Pfizer and BioNTech asked the FDA to authorize an additional booster dose for people 65 and older, based on evidence from Israel showing that a second booster at least four months after the first significantly lowered the risk for infection and severe disease in people 60 and older.

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 12 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 March 14, 2022, about 96.1 million people in the U.S. had received booster shots.

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 in these groups. 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). As of Jan. 4, immunocompromised children ages 5 to 11 are also eligible for this third dose four weeks after their second shot, though boosters are not yet recommended for this population.

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 has shown 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 from infection 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.

The question is if and when another shot will be needed. In Pfizer and BioNTech’s request to authorize a fourth shot, the companies said that data from Kaiser Permanente Southern California shows that the protection an initial booster provides against infection and severe disease caused by omicron wanes after three to six months.

Do Boosters Improve Immunity?

Yes. Data published by the CDC and peer-reviewed research published in medicals journals shows 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 had received just two vaccine doses.

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 were significantly lower among those who received a second booster, the companies say.

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, according to the agency. Rates of myocarditis after a booster are much lower than after a second vaccine dose, according to a CDC study released March 1.

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 and Johnson & Johnson’s doses are unchanged for booster shots.

The Pfizer-BioNTech vaccine is the only vaccine authorized for use in people under 18, and thus the only one available as a booster for this age group.

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 to find a location near you.

Are the Booster Formulas Being Changed to Match Emerging Variants?

The booster vaccine doses that are being given so far are the same formula as the initial vaccine doses.

But companies are working on versions of their vaccines that can target new variants, says Gregory Poland, MD, director of the Vaccine Research Group at the Mayo Clinic in Rochester, Minn. Modifying the mRNA vaccines to target a different strain is a relatively quick process. What’s unclear at this point, he says, is how the FDA will regulate these modified vaccines—whether it will treat them as new products (which could take a long time for approval or authorization) or more like annual flu vaccines (for which approval would be much faster).

Pfizer and BioNTech and Moderna say that they’re working on omicron-specific boosters but that a boost with currently available vaccines significantly raises infection-fighting antibody levels against omicron. On Jan. 25, Pfizer and BioNTech announced that they had begun a trial with an omicron-specific vaccine candidate. On Jan. 26, Moderna announced that it had begun a similar trial with its own omicron-specific candidate.

One preliminary animal study indicates that an omicron-specific booster doesn’t boost antibodies significantly more than the boosters already being given, but it’s not yet clear whether that will hold true in larger human trials.

Will We Need Boosters Forever?

Down the road it’s possible that we may need a regular booster against the coronavirus like we do against the flu, says Joshua Barocas, MD, an associate professor of medicine 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.

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