How Long Does a COVID Booster Shot Last?

Research suggests protection against severe illness could delay need for another dose in some

Seamless pattern of vaccines fighting against Omicron spikes on pink background

Dusan Stankovic / Getty Images

Rachel Nania,

AARP

En español

February 24, 2022

When it comes to the pandemic, it’s been a long winter — one of record-breaking COVID-19 infections and hundreds of thousands of lives lost. And throughout it, one thing has become clear: A booster shot is key to avoiding the ravages of the now-dominant omicron variant.

During December, unvaccinated adults ages 18 through 49 were 30 times more likely to be hospitalized than their boosted peers, federal data show. Looking at the 65-plus age group, the difference shoots up to 51 times more likely. What’s more, the risk of dying from COVID-19 during January was 41 times higher for unvaccinated adults than for those with their booster shot. “It’s very important to get boosted for omicron,” says David Montefiori, a professor and vaccine expert at Duke University School of Medicine’s Human Vaccine Institute.

How long does this protection last? “There are no real clear definitive answers,” says Alessandro Sette, a professor at La Jolla Institute for Immunology. But scientists are learning more every day. Here’s what we know so far about the durability of a booster shot and what that could mean for the future.

Booster protection wanes, but still deters serious illness

If you’re one of the more than 93 million Americans who received a COVID-19 booster in the fall or winter and you are not immunocompromised, a number of experts say you are likely still well protected against serious illness and death. Still, it’s important to keep in mind that the vaccines offer “a gradient of protection” that is influenced by a number of factors, including age, genetics, the immune system and underlying health conditions, says Gregory Poland, M.D., professor of medicine and infectious diseases at the Mayo Clinic in Rochester, Minnesota, and founder and director of Mayo’s Vaccine Research Group. “There is no light switch here.”

Research collected during the omicron wave and published by the Centers for Disease Control and Prevention (CDC) found that about two months after a Pfizer-BioNTech or Moderna booster shot, the vaccine’s effectiveness against hospitalization was around 90 percent. Four months out, it was about 80 percent, which top infectious disease expert Anthony Fauci, M.D., says “is still a good protective area.” It’s also considerably higher than the level of protection against hospitalization provided by two standard doses of an mRNA vaccine, which fell to about 54 percent roughly five months after vaccination.

Despite the initial decline, scientists say the strong degree of protection against severe outcomes could hold steady even longer in some people. The reason? We’re learning more about the various players on the body’s COVID-fighting team and how they’re mounting their defense when faced with the coronavirus.

B cells and T cells: It’s not all about the antibodies

Neutralizing antibodies, though commonly discussed, is only one key component in this defense. These germ-attacking proteins spike after vaccination or infection (both trigger their production) and circulate in the blood, keeping an eye out for the virus. If they recognize an invader, they’ll attempt to bind to the virus, interfering with its ability to infect the cells. However, omicron has complicated their efforts: According to the National Institutes of Health, antibodies generated by the COVID-19 vaccines “don’t recognize their targets as well in heavily mutated variants like omicron,” which helps to explain why we’ve seen so many breakthrough infections since the variant rose to dominance.

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What’s more, research suggests these neutralizing antibodies lose steam over time, and their levels drop off after several months.

That’s where the next line of defense comes in: specifically, B cells, which make the antibodies, and T cells, which patrol and destroy the cells infected with the virus.

“You can imagine that the B cells are soldiers that shoot out bullets, and the bullets are the antibodies. So once the attacker is gone, the soldiers stop shooting. It would be a waste of ammunition to keep on making antibodies for a virus that is no longer there,” Sette explains. If the virus comes back, “they are ready to go in a matter of days to mount a full-blown immune response again,” Sette says.

A new preprint study, first reported on by The New York Times, found that a third dose of an mRNA vaccine (Pfizer or Moderna) increases the power of these B cells, allowing them to “produce antibodies capable of clearing even diversified variants such as omicron” within a few days of recognizing an invader, the report’s authors note. This can help explain why a booster shot of an mRNA vaccine that was not “specifically designed to protect against variants is effective against variant-induced serious disease,” they write. The research, however, has not yet been peer reviewed.

“The B cells have this amazing capacity of continuing to evolve,” Sette explains, adding that even in the absence of an ongoing infection, “you have this continued maturation of the antibody response.”

What’s more, research from Sette and others shows that the majority of T cells — these are the cells that help to control and terminate an infection — generated after vaccination continue to recognize coronavirus variants, including omicron. “These cells won’t stop you from getting infected, but in many cases, they are likely to keep you from getting very ill,” Shane Crotty, a professor at La Jolla Institute for Immunology and a coauthor of the study published in Cell, said in a statement. (The data from the study stemmed from fully vaccinated, but not yet boosted, adults. The researchers are currently studying T cell responses in boosted individuals.)

It’s not clear how long these responses last, but B and T cell responses tend to persist for some time, experts say. According to Sette, T cells lasted more than a decade after infection with the SARS virus that was behind the 2003 outbreak in Asia.

“We’re still really learning a lot about what we call immune correlates of protection,” says Robert Atmar, M.D., a professor of medicine and infectious diseases at Baylor College of Medicine in Houston. “In other words, what part or parts of the immune system protect a person from getting infected, getting sick or getting very sick? There’s still a lot of new information coming out, and it looks like the cellular immunity is less affected by changes in variants.”

A second booster may make sense for some

Because of the staying power of these B and T cells, several experts interviewed by AARP say a second booster (amounting to a fourth shot for people who had Pfizer or Moderna for their first series and a third shot for those who had Johnson & Johnson the first go-round) may not be needed right away — at least for most healthy adults and in the absence of a more virulent variant. One prediction is that a second booster could be available in the fall — a time of year when many people also head to the pharmacy or doctor’s office to get their flu shots.

Some countries have already started the rollout of a fourth dose for older adults; Fauci has said that in the U.S. “recommendations, if needed, will be updated according to the data as it evolves.” He added, “For the immunocompetent people, a single booster shot continues to provide high levels of protection against severe disease caused by omicron.” (People who are immunocompromised are already eligible for a fourth dose of an mRNA vaccine.)

However, even if a second booster is recommended, that doesn’t mean we’ll necessarily have to keep going back for more every few months, though an annual booster is a possibility. One extra dose of the vaccine could be enough to keep the neutralizing antibody levels higher for longer, Montefiori says. An extra shot could also help the memory B cells continue to mature, so they are better prepared for future infections.

“At some point, though, you reach a plateau where you can keep boosting and the antibodies aren’t getting any better, the resting memory B cells aren’t going to continue to get any better — you’re going to have as many as the body’s going to make, and they’re going to be as mature as they’re going to get,” Montefiori says. “I don’t think we’re there with only three doses; I think we’ll get there with four doses. And for people with weaker immune systems, that will probably take five doses.”

In the meantime, if you haven’t received your first booster and are eligible — less than half of fully vaccinated Americans ages 12 and older have gone back for that booster dose — make sure you do that, Montefiori adds. It could protect you against serious illness from an omicron infection. It may also defend you from the wrath of any forthcoming variants.

“What we see with boosting is protection against omicron, which is very, very different from any other variants we’ve seen before it. So I am an optimist. I take that as a sign that boosting might help protect against future variants as well,” he says.

Also, it’s still important to keep up other preventive efforts that can lower your risk of disease, experts interviewed by AARP say, even as new cases of COVID-19 continue to fall in many areas of the country. “Wear a proper mask, properly” when you’re indoors with people who are not your family, Poland says. Try to maintain some physical distance between yourself and others, he adds, and make sure you’re getting your information from credible sources, like academic medical centers.

Also, take a look at infection rates in your own community, which can help you weigh your individual risk, Atmar suggests. (You can look at local levels of transmission on the CDC’s website here.) “And then stay tuned,” Poland says.

Rachel Nania writes about health care and health policy for AARP. Previously she was a reporter and editor for WTOP Radio in Washington, D.C. A recipient of a Gracie Award and a regional Edward R. Murrow Award, she also participated in a dementia fellowship with the National Press Foundation.

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