NEW YORK — The vaccines made by Pfizer-BioNTech and Moderna set off a persistent immune reaction in the body that may protect against the coronavirus for years, scientists reported Monday (June 28).

The findings add to growing evidence that most people immunised with the mRNA vaccines may not need boosters, so long as the virus and its variants do not evolve much beyond their current forms — which is not guaranteed. People who recovered from Covid-19 before being vaccinated may not need boosters even if the virus does make a significant transformation.

“It’s a good sign for how durable our immunity is from this vaccine,” said Dr Ali Ellebedy, an immunologist at Washington University in St Louis who led the study, which was published in the journal Nature.

The study did not consider the coronavirus vaccine made by Johnson & Johnson, but Dr Ellebedy said he expected the immune response to be less durable than that produced by mRNA vaccines.

Dr Ellebedy and his colleagues reported last month that in people who survived Covid-19, immune cells that recognise the virus lie quiescent in the bone marrow for at least eight months after infection. A study by another team indicated that so-called memory B cells continue to mature and strengthen for at least a year after infection.

Based on those findings, researchers suggested that immunity might last for years, possibly a lifetime, in people who were infected with the coronavirus and later vaccinated. But it was unclear whether vaccination alone might have a similarly long-lasting effect.

Dr Ellebedy and his colleagues recruited 41 people — including eight with a history of infection with the virus — who were immunised with two doses of the Pfizer-BioNTech vaccine.

Dr Ellebedy’s team found that 15 weeks after the first dose of vaccine, a specialised structure called the germinal centre that forms in lymph nodes was still highly active in all 14 of the participants, and that the number of memory cells that recognised the coronavirus had not declined.

The results suggest that a vast majority of vaccinated people will be protected over the long term — at least, against the existing coronavirus variants. But older adults, people with weak immune systems and those who take drugs that suppress immunity may need boosters; people who survived Covid-19 and were later immunised may never need them at all.

This article originally appeared in The New York Times.