How Long Does COVID-19 Immunity Last?

I called several scientists to talk me through the study and ease my apocalyptic anxiety. Their response: Please calm down—but don’t expect us to make you feel entirely relaxed. (I also reached out to several co-authors of the Kings College paper, but did not hear back.)

“I was definitely very worried when I saw the headlines,” said Shane Crotty, a virologist at the La Jolla Institute for Immunology. “But then I looked at the data. And actually, looking at the data, I feel okay about it.”

Acquired immunity is cellular memory. When our bodies fight off an infection, we want our immune systems to remember how to defeat it again, like a person who, after solving a big jigsaw puzzle, recognizes and remembers how to set the pieces the next time. The whole point of vaccination is to teach the immune system those same puzzle-solving lessons without exposing it to the full virus.

This is why the Kings College study initially seemed so dreadful. It found that the number of certain active antibodies—called “neutralizing antibodies”—declined significantly between tests, especially in patients with mild or no symptoms. Antibody levels are one proxy for the immune system’s memory. If they plunge quickly, that might mean that our immune system can’t remember how to solve COVID-19 for more than a few months at a time, dooming us to start from square one with each new exposure. No COVID-19 researchers are rooting for antibody levels to decline so quickly. Everyone I spoke with acknowledged that the study might reveal something important and concerning.

But overall, the scientists converged on three reasons to hold out a bit of skepticism about the most apocalyptic headlines.

First, our immune system is a mysterious place, and the Kings College study looked at only one part of it. When a new pathogen enters the body, our adaptive immune system calls up a team of B cells, which produce antibodies, and T cells. To oversimplify a bit, the B cells’ antibodies intercept and bind to invading molecules, and the killer T cells seek and destroy infected cells. Evaluating an immune response without accounting for T cells is like inventorying a national air force but leaving out the bomber jets. And, in the case of COVID-19, those bomber jets could make the biggest difference. A growing collection of evidence suggests that T cells provide the strongest and longest-lasting immunity to COVID-19—but this study didn’t measure them at all.

“To look at just one part of the immune response is woefully incomplete, especially if many COVID patients rely more on T cells,” said Eric Topol, a cardiologist and the founder and director of the Scripps Research facility. He pointed me to a study from France’s Strasbourg University Hospital, which found that some people recovering from COVID-19 showed strong T-cell responses without detectable antibodies. “There is a chance that if a similar longitudinal study looked at T-cell response, the outcome would be far more optimistic,” he said.