How Long Does Vaccine Protection Last?
Nearly 18 months after COVID-19 first appeared in Wuhan, China, researchers are still learning new things about the virus and the vaccines developed to fight it. Among the questions scientists want to answer: How long do vaccines protect against the virus?
A study published in the journal Science that looked at the immune response among people who contracted COVID-19 found that protection lasts at least six months and possibly as much as eight months as immunity slowly trails off after the initial infection.
That study looked at the various pieces of the immune system — B cells, T cells and others — that form the body’s “memory” when it comes to recognizing a disease and fighting it in the future.
After the initial infection, the body’s immune response spikes at about 20 days then tapers off to a point where it offers a consistent level of immunity. Because COVID-19 is a new disease, it remains unclear exactly how long that immunity lasts. Eight months has been the maximum observed so far.
Vaccinations provide a safe way to simulate an infection. By doing so, they kick-start the body’s immune reaction without requiring someone to contract a disease naturally.
In some cases, vaccines provide stronger immunity than do actual infections. Based on the immunity that comes from COVID-19 infections, researchers believe vaccination-derived immunity will last about the same length of time.
“There’s a lot of different arms of the immune system recognizing the virus,” Daniela Weiskopf, a co-author of the study and a researcher at the La Jolla Institute for Immunology in California, told The Washington Post.
Those many arms also should protect against mutant strains of the virus, such as B.1.17 and B.1.135 that are circulating in many African countries.
“So, if you have a mutation, it wouldn’t evade all these different arms,” Weiskopf said.
Because COVID-19 vaccines were issued on an emergency basis, scientists were unable to conduct the type of long-term phase 3 studies they usually do for vaccines. So, in effect, they are still learning how the COVID-19 vaccines function in the human body and how long their benefits last.
At the moment, it seems likely people will need annual booster shots to support their immunity to COVID-19, according to public health experts.
With nearly 100 COVID-19 vaccines in some form of development, scientists will continue to attack the virus in new ways.
“Vaccine-derived immunity can sometimes be stronger and longer-lasting, but this is by no means always the case, and so with COVID-19 vaccines the jury is still out,” science writer Priya Joi wrote in the blog of Gavi, the Vaccine Alliance.
One thing is certain: Vaccinations protect people from severe symptoms and, so far, have completely stopped people from dying of COVID-19.
For that reason, public health officials such as John Nkengasong, director of the Africa Centres for Disease Control and Prevention, continue to urge people to get vaccinated against COVID-19. Any vaccination is better than no vaccination at all, Nkengasong has said repeatedly.
Even if full immunity decreases over time, the body remains primed to take on the virus, keeping future reinfections less serious than if the person were never vaccinated, according to the study.
“Even if antibody levels wane and you get reinfected or you get infected with a variant, the memory B cells — if you have enough of them — will respond very quickly and prevent that severe disease,” David Topham, a professor of microbiology and immunology at the U.S.’s University of Rochester, told The Washington Post.