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Researchers at Harvard Medical School have discovered an increased persistence of certain protective antibodies in patients who survived increased severity cases of COVID-19.

The research — published in Science Immunology earlier this month — identified antibodies that persist in blood samples four months after COVID-19 infection.

Jason B. Harris, an associate professor of pediatrics at HMS and co-senior author of the study, said the antibodies the researchers observed are broadly classified into three types: IgA, IgM, and IgG. The researchers were especially excited to find that IgG — which often serves as a neutralizing antibody that can block the virus from entering a cell — showed signs of longevity.

“For a lot of viruses, neutralizing antibodies predict whether you are protected from future infection,” Harris said. “Because COVID-19 is a new infection we are still learning about, we were especially interested to know whether that infection resulted in long-lasting immune memory. The persistence of antibodies, specifically IgG, is a very encouraging sign that COVID-19 does induce long-lasting immunity.”

Harris also said having antibodies such as IgA and IgM that demonstrate shortened persistence can be helpful to clinicians to identify both whether or not a patient might have been infected with SARS-CoV-2 as well as the timeline of infection.

“As a doctor, I see many people who want to know whether or not they have had COVID-19, even if it was in the past or recent past, because people might get sick but not know why they got sick,” Harris said. “Unless you’re testing them really early in the disease, PCR tests might not be as helpful in determining later on if someone was infected with COVID-19.”

Anita S. Iyer, a postdoctoral research fellow at HMS and first author on the study, said while the study provides promising findings, some questions still remain. The current study tracked antibody persistence over four months, follow-up studies will aim to track persistence over a year.

In addition, many of the blood samples within the study came from patients with severe COVID-19 infections who had been hospitalized at Massachusetts General Hospital. Iyer said researchers have yet to discover how antibody persistence might differ between severe and mild cases of infection.

“Since patients with asymptomatic or mild cases were able to mount resistance against infection, these patients must also have produced antibodies, right?” Iyer said. “However, we have yet to track more mild infections, and it is possible we might see a difference in persistence of antibodies produced in response to a mild infection compared to a severe infection.”

Richelle C. Charles, an assistant professor of medicine and co-senior author of the study, said while she believes patients with COVID-19 can develop immunity, scientists still do not know “exactly what the full protective immune response to COVID is.”

“I would say that neutralizing antibody titers is a protective response, but I would also want to look if there are other protective responses that might in addition be important in protection against subsequent infection,” Charles said.

—Staff writer Meera S. Nair can be reached at meera.nair@thecrimson.com.