COVID-19 immunity may last for years, data shows.

How long might immunity to the coronavirus last? Years, maybe even decades, according to a new study — the most hopeful answer yet to a question that has shadowed plans for widespread vaccination.

Eight months after infection, most people who have recovered still have enough immune cells to fend off the virus and prevent illness, the new data show. A slow rate of decline in the short term suggests, happily, that these cells may persist in the body for a very, very long time to come.

The research, published online, hasn’t been peer-reviewed or published in a scientific journal. But it’s the most comprehensive and long-ranging study of immune memory to the coronavirus yet.

“That amount of memory would likely prevent the vast majority of people from getting … severe disease, for many years,” said Shane Crotty, a virologist at the La Jolla Institute of Immunology who co-led the new study.

The findings likely will come as a relief to experts worried that immunity to the virus might be shortlived, and that vaccines might have to be administered repeatedly to keep the pandemic under control.

And the research squares with another recent finding: that survivors of SARS, caused by another coronavirus, still carry certain important immune cells 17 years after recovering.

The findings are consistent with encouraging evidence emerging from other labs.

Researchers at the University of Washington showed that certain “memory” cells produced after infection with the coronavirus persist for at least three months in the body.

A study published lastweek also found that people who have recovered from COVID-19 have powerful and protective killer immune cells even when antibodies aren’t detectable.

These studies “are all by and large painting the same picture, which is that once you get past those first few critical weeks, the rest of the response looks pretty conventional,” said Deepta Bhattacharya, an immunologist at the University of Arizona.

Yale University immunologist Akiko Iwasaki said she wasn’t surprised that the body mounts a longlasting response because “that’s what is supposed to happen.” Still, she was heartened by there search: “This is exciting news.”

A small number of infected people in the new study didn’t have long-lasting immunity after recovery, perhaps because of differences in the amounts of coronavirus they were exposed to. But vaccines can overcome that individual variability, said Jennifer Gommer man, an immunologist at the University of Toronto.

“That will help in focusing the response,” she said.