“Sterilization of immunity does not happen very often – this is not the norm,” said Alessandro Cete, an immunologist at the Institute of Immunology in La Jolla and co-leader of the study.
More often, people become infected a second time with a specific pathogen, and the immune system recognizes the invader and quickly extinguishes the infection. In particular, the coronavirus slowly causes damage by giving the immune system enough time to start working.
“It can stop quickly enough so that you not only don’t have any symptoms, but you’re not contagious,”
Dr. Seth and his colleagues recruited 185 men and women between the ages of 19 and 81 who had recovered from Covid-19. Most have mild symptoms that do not require hospitalization; most provided only one blood sample, but 38 provided multiple samples over many months.
The team tracked four components of the immune system: antibodies, B cells that produce more antibodies as needed; and two types of T cells that kill other infected cells. The idea was to build a picture of the immune response over time by looking at its components.
“If you look at just one, you can really miss the full picture,” Dr. Croti said.
He and colleagues found the antibodies to be persistent, with a moderate drop six to eight months after infection, although there was a 200-fold difference in levels among participants. T-cells showed only a slight, slow breakdown in the body, while B-cells grew – an unexpected finding, researchers can not quite explain.
The study is the first to describe the immune response to a virus with such granular detail, experts said. “We certainly don’t have priorities here,” Dr. Homerman said. “For the first time, we are learning about some of the dynamics of these populations over time.”