[A new] study, published January 6 in Science, contrasts with earlier findings that suggested covid-19 immunity could be short-lived, putting millions who’ve already recovered at risk of reinfection. That predicament wouldn’t have been a total surprise, since infection by other coronaviruses generates antibodies that fade fairly quickly. But the new study suggests reinfection should only be a problem for a very small percentage of people who’ve developed immunity—whether through an initial infection or by vaccination.
In fact, the new study does show that a small number of recovered people do not have long-lasting immunity. But vaccination ought to offset that problem by ensuring herd immunity in the larger population.
The researchers found that antibodies in the body declined moderately after eight months, although levels varied wildly between individuals. But T-cell numbers declined only modestly, and B-cell numbers held steady and sometimes inexplicably grew. That means that despite decreases in free-flowing antibodies, the components that can restart antibody production and coordinate an attack against the coronavirus stick around at pretty high levels. [Researcher Shane] Crotty adds that the same mechanisms that lead to immune memory after infection also form the basis for immunity after vaccination, so the same trends ought to hold for vaccinated people as well.