Participants with a prior case of disease showed cells in their bone marrow up to 4 months after their initial infection.
A recent study conducted by investigators from the Washington University School of Medicine in St. Louis has discovered that mild cases of COVID-19 provided individuals with immune cells that create antibodies against the virus for lasting protection.
Results from the study were published in the journal Nature.
"People with mild cases of COVID-19 clear the virus from their bodies two to three weeks after infection, so there would be no virus driving an active immune response seven or 11 months after infection," Ali Ellebedy, senior author on the study said. "These cells are not dividing. They are quiescent, just sitting in the bone marrow and secreting antibodies. They have been doing that ever since the infection resolved, and they will continue doing that indefinitely."
For the study, investigators elaborated on work that they were conducting which was tracking antibody levels in blood samples from individuals who had survived an infection with COVID-19.
The team obtained bone marrow samples from 18 of 77 participants who were enrolled in the previous study 7 to 8 months after their initial infection.
They then compared those samples to samples from 11 people who had never been infected with the disease.
Findings from the study showed that 15 of the participants who had COVID-19 contained antibody-producing cells specifically targeting the SARS-CoV-2 virus in their samples. Additionally, the investigators found the cells in 5 samples from individuals who came back for a second sample 4 months later.
"Last fall, there were reports that antibodies wane quickly after infection with the virus that causes COVID-19, and mainstream media interpreted that to mean that immunity was not long-lived," Ellebedy said. "But that's a misinterpretation of the data. It's normal for antibody levels to go down after acute infection, but they don't go down to zero; they plateau. Here, we 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. That's strong evidence for long-lasting immunity."