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.

Second, the immunologist Shane Crotty told me that while the decline in antibodies was troubling, it was hardly catastrophic. “It’s not unusual to have fading antibody response after several months,” he said.