Aacquired immunity is cellular Memory. When our body is fighting an infection, we want our immune system to remember how to beat it again, like a person who, after solving a big puzzle, recognizes and remembers how to put the pieces down next time. The goal of immunization is to teach the immune system these same puzzle-solving lessons without exposing it to the whole virus.
This is why the KCL study seemed so terrible at first. He found that the number of certain active antibodies – called “neutralizing antibodies” – decreased significantly between tests, especially in patients with mild or no symptoms. Antibody levels are a proxy for the memory of the immune system. If they dive quickly, it could mean that our immune system can no longer remember how to fix COVID-19 for more than a few months at a time, ordering us to go back to square one with each new exposure. No COVID-19 researcher wants antibody levels to drop so quickly. Everyone I spoke with acknowledged that the study may reveal something important and concerning.
But overall, scientists have converged on three reasons to keep some skepticism about the most apocalyptic titles.
First, our immune system is a mysterious place, and the KCL study looked at only 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 make things a little simpler, antibodies to B cells intercept and bind to invading molecules, and killer T cells seek out and destroy infected cells. Evaluating an immune response without taking T cells into account is like taking an inventory of a national air force, but leaving out bomber jets. And, in the case of COVID-19, these bombers 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 did not measure them at all.
“Examining just one part of the immune response is woefully incomplete, especially if many COVID patients rely more on T cells,” said Eric Topol, cardiologist and founder and director of the Scripps Research Center. He pointed to a study from the French University Hospital in Strasbourg, which found that some people recovering from COVID-19 had strong T cell responses without detectable antibodies. “There is a chance that if a similar longitudinal study looked at the T cell response, the result would be much more optimistic,” he said.