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How Long Does a COVID Booster Shot Last?

Effectiveness wanes over time, but protection against critical illness can persist longer

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The first coronavirus vaccines became available in the U.S. in late 2020, and ever since, one thing has become clear: The initial shots and subsequent boosters have saved countless lives — some studies estimate more than 3 million. 

Vaccinated adults who received a dose of the most recent booster, what’s known as a bivalent vaccine, are 5.3 times less likely to die from COVID-19 than their unvaccinated peers, March data from the Centers for Disease Control and Prevention (CDC) shows. Their odds of surviving a coronavirus infection are also greater than vaccinated adults who skipped out on the new booster, which has been available since September 2022. 

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And a study published in The New England Journal of Medicine in February 2023 found that the bivalent shots were 37 percent more effective at preventing severe COVID-19 than the original boosters. But how long does this protection last? 

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.

Many factors determine length, degree of COVID protection

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.”

Federal data shows the boost in protection from infection and illness afforded by the boosters, including the bivalent booster, tends to wane after a few months. That doesn’t mean the body becomes defenseless overnight, however.

“We begin to see within 60 days that the quality of your protection against infection starts to decrease. And, in fact, by six months or so, you have very little protection against infection. But your protection against severe disease, like death and hospitalization, remains pretty good. It’s not 100 percent — it never is. But it’s pretty good,” Poland says. 

Several factors influence overall immunity. Antibodies are the vanguard of the immune 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.


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However, omicron and its subvariants, like the now-dominant XBB.1.5, are better at sneaking around these antibodies, which is why people who have been vaccinated or infected, or both, can still get COVID-19. 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. These key players are sometimes referred to as “memory cells.” 

The B cells “have this amazing capacity of continuing to evolve,” says Alessandro Sette, a professor at La Jolla Institute for Immunology. Research has shown that even months after vaccination, the B cells keep working to make stronger, more effective antibodies. 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 COVID vaccination continue to recognize coronavirus variants, including omicron. 

“It’s the T cells that protect you against severe infection, hospitalization and death,” Poland says, noting that the protection might not be as robust in immune-compromised individuals. CDC data from January through May show that even though protection against hospitalization after a bivalent booster drops over time, it’s more sustained against critical illness. 

It’s not clear how long these responses last, but B and T cell responses tend to persist for some time, experts say. 

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How often are COVID boosters needed? 

Health officials are still working to determine how frequently people should get vaccinated against COVID-19. For many, it may be an annual shot, like the flu vaccine. People more vulnerable to severe illness, however, may need a boost more frequently. (In April, health officials gave adults 65 and older and immunocompromised individuals the OK to get a second dose of the bivalent booster, as long as it’s been at least four months since their last one.) 

Vaccine manufacturers will likely update the vaccine to better target the virus as it evolves. Scientists are also working to develop a vaccine that could be longer-lasting and more effective at preventing a coronavirus infection, Poland says.

In the meantime, health experts are urging people who haven’t received the bivalent booster to get it. Only about 17 percent of the U.S. population has received this shot, federal data shows. Wearing a mask indoors — especially if cases are increasing in your area — can also help keep you healthy. 

If you do get COVID-19, Poland says, make sure you talk to your doctor about treatments. There are antiviral pills that can help keep you out of the hospital. “The sooner after getting infected and having symptoms that you get treated, the better the result,” he says. 

Editor’s note: This story, first published Feb. 24, 2022, has been updated to reflect new information.

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