Mild COVID-19 induces lasting antibody protection: Study
Months after recovering from mild cases of COVID-19, people still have immune cells which produce antibodies against the novel coronavirus, according to a study published on Monday in the journal Nature. The researchers from Washington University School of Medicine in St. Louis, US, noted that such cells could persist for a lifetime, churning out antibodies all the while.
Antibody levels go down but don't vanish
The study suggests that mild cases leave those infected with lasting antibody protection and that repeated bouts of illness are likely to be uncommon. "Last fall, there were reports that antibodies wane quickly after infection. It's normal for antibody levels to go down after acute infection, but they don't go down to zero; they plateau," said senior author of the study Ali Ellebedy.
How do antibodies work in a human body?
The researchers found antibody-producing cells in people 11 months after first symptoms. These cells will live and produce antibodies for the rest of people's lives, and that's strong evidence for long-lasting immunity. During a viral infection, antibody-producing immune cells rapidly multiply and circulate in the blood, driving antibody levels sky-high. Once the infection is resolved, most such cells die, and blood antibody levels drop.
Some antibody-producing cells settle in the bone marrow
A small population of antibody-producing cells, called long-lived plasma cells, migrate to the bone marrow and settle in. In the bone marrow, these cells continually secrete low levels of antibodies into the bloodstream to help guard against another encounter with the virus. Ellebedy and colleagues were already working on a project to track antibody levels in blood samples from COVID-19 survivors.
Who all participated and how was the study conducted?
The researchers enrolled 77 participants who were giving blood samples at three-month intervals starting about a month after initial infection. Most participants had had mild cases of COVID-19, only six had been hospitalized. They obtained bone marrow from 18 participants seven or eight months after their initial infections. Five of them came back four months later and provided a second bone marrow sample.
Antibodies were detectable even 11 months after infection
For comparison with the COVID-19 infected people, the scientists obtained bone marrow from 11 people who had never suffered from the infection. They found that antibody levels in the blood of the COVID-19 participants dropped quickly in the first few months after infection and then mostly leveled off, with some antibodies detectable even 11 months after infection.
No antibody-producing cells found in those who were never infected
Fifteen of the 19 bone marrow samples from people who had had COVID-19 contained antibody-producing cells specifically targeting the virus that causes COVID-19. Such cells could still be found four months later in the five people who came back to provide a second bone-marrow sample. According to the researchers, none of the 11 people who had never had COVID-19 had such antibody-producing cells.
