Whether we would develop immunity to COVID-19, or how long that would last if we did, has been a mystery since the early months of the pandemic.
However, two new studies are helping us better understand how our immune systems adapt to infection, and what that might mean for vaccination.
The studies, published in May, find that infection-induced immunity might last months or longer. But experts believe vaccination may lengthen the duration of this immunity.
Another important finding from both studies is that many people who have recovered from COVID-19 and later receive an mRNA vaccine (like the Moderna or Pfizer-BioNTech vaccine) may not need booster shots.
Immunity in people with prior infection ‘should’ be effective against virus variants
Both studies examined people exposed to the coronavirus roughly a year earlier.
According to one study published in Nature, immune cells located in our bone marrow keep a “memory” of the coronavirus and are able to create protective antibodies to prevent reinfection. The other study, which is not yet peer-reviewed, found these immune cells can mature and strengthen for about a year after infection.
“The data suggest that immunity in convalescent individuals will be very long lasting and that convalescent individuals who receive available mRNA vaccines will produce antibodies and memory B cells that should be protective against circulating SARS-CoV-2 variants,” the study authors wrote.
How the immune response works
According to Dr. Miriam Smith, chief of infectious disease at Long Island Jewish Forest Hills, Northwell Health in New York, our immune systems include B cells, which are a type of white blood cell (WBC) responsible for humoral immunity.
“They originate and mature in the bone marrow, then migrate to the spleen and lymph nodes,” she told Healthline. “B cells become activated in response to an antigen, a virus, or bacterium.”
Smith explained that B cells have receptors on their surface that can bind to these pathogens.
“With help from the T cells, another component of the immune system, the B cells will differentiate into plasma cells to produce antibodies that will trap the virus or bacterium invader and allow other cells (macrophages) to destroy the invader,” Smith said.
She said that after infection, the “memory” B cells stay around, so if that same virus or bacterium invades again, the immune system “remembers” and reactivates to fight it off.
Had COVID-19? You should still get vaccinated
“It’s still important for those people to be vaccinated,” said Dr. Len Horovitz, pulmonary specialist at Lenox Hill Hospital in New York. “Their immunity, as far as we know, may not be long-lived more than the 11 months that were documented.”
He explained that this means people who’ve had the disease cannot rely on previous infection to achieve immunity the way people could with measles, mumps, and rubella, “and those aren’t necessarily permanent immunity, but let’s say lifelong,” he added.
According to Horovitz, reinfections don’t necessarily mean a milder case of the disease.
“It can be milder, it can be the same in degree of severity, and it can be worse,” he explained. “So, there’s a lot we don’t know.”
According to the Centers for Disease Control and Prevention (CDC)Trusted Source, reinfection means someone got sick once, recovered, and then got sick again. The CDC emphasizes that although uncommon, reinfection can happen with COVID-19.
“We do not know the exact rate [of reinfection],” Horovitz said. “We know it can occur, we know that it’s not common, but it’s not rare.”
If reinfection is possible, Horvitz pointed out, “then you can spread it to other people.”
He said this means people who contract another infection will not contribute to herd immunity.
“So, it is important if you’ve had COVID not to rely on the fact that you’ve had it and probably won’t get it again,” Horvitz said. “And you need to be immunized because the antibodies that you get from infection are different from the antibodies that you get from immunization. They’re two different measurable antibodies.”
More booster shots in the future?
These new studies also suggest that a majority of people who have recovered from COVID-19 and were later immunized with one of the mRNA vaccines will not need booster shots to maintain protection against the virus.
However, vaccinated people who didn’t have a previous infection will likely require booster shots, as will the small number of people who had the disease but didn’t produce a sufficiently strong immune response.
According to Horovitz, booster shots may likely help.
“In fact, there was an article this week in The New York Times where they looked at the response of people who’ve had COVID and are vaccinated, and they had an unbelievable immune response — much more than somebody who was COVID naïve [hadn’t had a previous infection],” he said.
“So, someone who’s had COVID-19, gets immunized, then they never have to have a booster,” he continued. “They have more immunity than someone who’s been vaccinated [and never had a previous infection], it would seem.”
The bottom line
Two recently published studies have found that people who recover from COVID-19 develop antibodies that may last almost a year.
Experts say that reinfection, while uncommon, can still happen — and being vaccinated with one of the mRNA vaccines (like the Moderna of Pfizer-BioNTech vaccine) can significantly boost immunity.
Experts also say that people who have had COVID-19 may not require booster shots to maintain protection, since the mRNA vaccines elicit such a powerful immune response in this group.
However, experts caution that people who haven’t had a previous infection will likely need them.