“Immunity sterilization doesn’t happen very often – it’s not the norm,” said Alessandro Sette, immunologist at the La Jolla Institute of Immunology and co-lead of the study.
More often than not, people are infected a second time with a particular pathogen, and the immune system recognizes the invader and quickly quenches the infection. The coronavirus in particular is slow to damage, which gives the immune system enough time to kick in.
“It can be stopped quickly enough so that not only are you free of symptoms, but also contagious,” said Dr. Sette.
Dr Sette and his colleagues recruited 185 men and women, aged 19 to 81, who had recovered from Covid-19. The majority had mild symptoms that did not require hospitalization; most provided a single blood sample, but 38 provided multiple samples over several months.
The team tracked four components of the immune system: antibodies, the B cells that make more antibodies when needed; and two types of T cells that kill other infected cells. The idea was to paint a picture of the immune response over time by examining its constituents.
“If you only look at one, you can really miss the full picture,” Dr Crotty said.
He and his colleagues found that the antibodies were long lasting, with modest drops six to eight months after infection, although there was a 200-fold difference in levels among participants. T cells have only shown a slight, slow breakdown in the body, while B cells have increased in number – an unexpected finding that researchers can’t quite explain.
The study is the first to map the immune response to a virus in such detail, experts said. “Of course, we don’t have a prior here,” Dr. Gommerman said. “We are learning, I think for the first time, about some of the dynamics of these populations over time.”