In a new study from Washington University in St. Louis, researchers found that months after recovering from mild cases of COVID-19, people still have immune cells in their body pumping out antibodies against the virus that causes COVID-19.
Such cells could persist for a lifetime, churning out antibodies all the while.
The findings suggest that mild cases of COVID-19 leave those infected with lasting antibody protection and that repeated bouts of illness are likely to be uncommon.
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 off, and blood antibody levels drop.
The key to figuring out whether COVID-19 leads to long-lasting antibody protection lies in the bone marrow.
In the study, the team examined whether those who have recovered from mild cases of COVID-19 harbor long-lived plasma cells that produce antibodies specifically targeted to SARS-CoV-2, the virus that causes COVID-19.
They 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.
The team obtained bone marrow from 18 of the participants seven or eight months after their initial infections. Five of them came back four months later and provided a second bone marrow sample.
For comparison, the scientists also obtained bone marrow from 11 people who had never had COVID-19.
As expected, 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.
Further, 15 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.
None of the 11 people who had never had COVID-19 had such antibody-producing cells in their bone marrow.
The team says 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.
People who were infected and never had symptoms also may be left with long-lasting immunity, the researchers speculated.
But it’s yet to be investigated whether those who endured more severe infection would be protected against a future bout of the disease.
The team says Inflammation plays a major role in severe COVID-19, and too much inflammation can lead to defective immune responses.
But on the other hand, the reason why people get really sick is often that they have a lot of viruses in their bodies, and having a lot of virus around can lead to a good immune response.
If you care about COVID-19, please read studies about these 2 blood types linked to lower risk of severe COVID-19 and findings of this mental problem is a key sign of COVID-19 in frail, older people.
For more information about COVID-19 and your health, please see recent studies about this surgery could help reduce severity of COVID-19 and results showing that COVID-19: when are you most infectious.
The study is published in Nature. One author of the study is Ali Ellebedy, Ph.D.
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