People who survive severe COVID-19 infections have protective antibodies for months

reviewed by Emily Henderson, Bachelor of ScienceOct 9, 2020

People who survive severe COVID-19 infections have long-lasting immune responses against the virus, according to a new study led by researchers at Massachusetts General Hospital (MGH).

The study, published in Science immunology, offers hope that people infected with the virus will develop lasting protection against re-infection. The study also shows that antibody measurement can be an accurate tool for tracking the spread of the virus in the community.

The immune system produces proteins called antibodies in response to SARS-CoV-2, the virus that causes COVID-19.

But there is a large knowledge gap in terms of how long these antibody responses last.. “

Richelle Charles, MD, study author and principal investigator, Division of Infectious Diseases, Massachusetts General Hospital

To find out, she and her colleagues obtained blood samples from 343 COVID-19 patients, most of whom had severe cases. Blood samples were taken up to four months after the patient’s symptoms appeared.

Plasma from blood was isolated and applied to laboratory plates coated with the receptor-binding domain (RBD) of the virus “spike” protein, which binds to cells and causes infection.

The team studied how different types of antibodies in plasma bind to RBD. The results were compared with blood samples obtained from more than 1,500 people before the pandemic.

The researchers found that measuring an antibody called immunoglobulin G (IgG) was very accurate in identifying infected patients who had symptoms for at least 14 days.

Since the standard PCR (nasal swab) test for SARS-CoV-2 loses sensitivity over time, it will be helpful to augment it with an antibody test in patients who have had symptoms for at least eight days (at which point 50 percent produce antibodies). Identify some positive cases that might otherwise be missed, says Charles.

The researchers found that IgG levels remained elevated in these patients for four months and were associated with the presence of protective neutralizing antibodies, which also demonstrated a small decrease in activity over time. “That means people are very likely to be protected during that period of time,” says Charles. “We show that key antibody responses to COVID-19 persist.”

In another finding, Charles and his colleagues showed that people infected with SARS-CoV-2 had immunoglobulin A (IgA) and immunoglobulin M (IgM) responses that were relatively short-lived, declining to low levels in about two and a half months. less, on average.

“We can now say that if a patient has IgA and IgM responses, they have likely been infected with the virus in the past two months,” says Charles.

Knowing the duration of the immune response to IgA and IgM will help scientists obtain more accurate data on the spread of SARS-CoV-2, explains Jason Harris, MD, a pediatric infectious disease specialist at MGH and a co-lead author of the study.

“There are many infections in the community that we do not detect by PCR testing during acute infection, and this is especially true in areas where access to testing is limited,” he says. “Knowing how long antibody responses last is essential before we can use antibody tests to track the spread of COVID-19 and identify the ‘hot spots’ of the disease.”