Patients who survive serious coronavirus infection have immune responses against the virus that lasts months, according to a recent Massachusetts General Hospital study, offering hope about protection from reinfection.

Doctors have long known that the immune system produces antibodies in response to COVID-19 infection, but “there is a big knowledge gap in terms of how long these antibody responses last,” said Dr. Richelle Charles, investigator in the division of infectious diseases at MGH and a senior author of the research.

Charles and her team got blood samples from 343 coronavirus patients, most with severe cases, and found that levels of an antibody called immunoglobulin G stayed elevated in the patients for four months and had neutralizing properties.

“That means that people are very likely protected for that period of time,” said Charles. “We showed that key antibody responses to COVID-19 do persist.”

The blood samples were taken from the patients up to four months after the onset of symptoms and plasma was isolated to see how different types of antibodies bound to the part of the virus that leads to infection.

The authors wrote, “The observation that (immunoglobulin G) and neutralizing antibody responses persist is encouraging, and suggests the development of robust systemic immune memory in individuals with severe infection.”

The patients in the study had very serious cases of coronavirus, 93% needing hospitalization.

“These findings are expected to have significant implications for protective immunity in a population which clearly is vulnerable to poor outcomes when exposed,” according to the researchers.

Charles and her colleagues also found that people infected with the coronavirus had other antibody responses that were short-lived and that declined to low levels within about two and a half months or less.

Charles said patients with those responses were likely infected with the virus within the last two months.

Researchers also found that measuring immunoglobulin was highly accurate in identifying infected patients who were sick for at least two weeks.

Since a standard nasal swab test can lose accuracy over time, researchers said augmenting it with an antibody test could help catch some positive cases that may have otherwise gone unnoticed.

Dr. Jason Harris, a pediatric infectious disease specialist at MGH and co-senior author of the study said, “There are a lot of infections in the community that we do not pick up through PCR testing during acute infection, and this is especially true in areas where access to testing is limited.”

“Knowing how long antibody responses last is essential before we can use antibody testing to track the spread of COVID-19 and identify ‘hot spots’ of the disease,” said Harris.

The authors write in the study that there has been “widespread misperception that antibody testing may be inaccurate.”

But, they say the study provides confidence that such measures can improve epidemiological investigations in public health efforts.


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