ST. LOUIS — Researchers here have discovered cells in the bone marrow of COVID-19 survivors that were still producing antibodies against the virus months after recovery, suggesting immunity may last far longer than once thought.
In a study released Monday in Nature, researchers show that among a group of 19 participants who previously had mild cases of COVID-19, 15 had antibody-producing cells in their bone marrow that target the virus that causes COVID-19.
“That’s strong evidence for long-lasting immunity,” said Ali Ellebedy, an associate professor at Washington University and senior author of the study.
The researchers took bone marrow samples from 18 participants seven to eight months after their initial infections. The cells were still found four months later in five participants who returned.
The researchers did not find the antibody-producing cells in a control group of 11 people who had never had the virus.
Ellebedy said Washington University researchers are also in the process of studying individuals who have been vaccinated.
The bone marrow work stemmed out of an ongoing study at Washington University, where researchers were tracking antibody levels in the blood of 77 participants, most of whom had mild cases of COVID-19. Their data showed antibody levels in the blood dropping quickly in the first few months of infection, then leveling, with still detectable amounts 11 months after infection.
The researchers acknowledged that the study only looked at the bone marrow of people who had mild cases of the virus, not those who had asymptomatic cases, or moderate or severe cases. And Ellebedy said that the age group of the participants was relatively young, so it is unclear whether an older group of individuals would have shown the same immune response. The participants ranged from 30 to 69 years old.
Dr. Sharon Frey, clinical director for St. Louis University’s Center for Vaccine Development, said scientists have suspected the presence of these cells, because they are found with other viruses, like influenza.
Still, said Frey, who was not involved in the study, the findings are positive, and exciting.
The body’s response to COVID-19 is complex, Frey said, and the cells are “just a piece of the overall immune response.” There are still many unknowns about how long the protection will last, and how protective they will be against different variants of the virus.
“It’s just a piece of the puzzle,” Frey said. “There’s a lot more work that needs to be done to research this aspect. A lot of that research is going to rely on the passage of time.”