Protective antibodies persist for months in survivors of ser
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People who survive serious 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 reinfection. The study also demonstrates that measuring antibodies 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 big knowledge gap in terms of how long these antibody responses last," says researchers. To find out, they obtained blood samples from 343 patients with COVID-19, most of whom had severe cases. The blood samples were taken up to four months after a patient's symptoms emerged.

The blood's plasma was isolated and applied to laboratory plates coated with the receptor-binding domain (RBD) of the virus's "spike" protein, which attaches to cells, leading to infection. The team studied how different types of antibodies in the plasma bound to RBD. The results were compared to blood samples obtained from more than 1,500 individuals prior to the pandemic.

The researchers found that measuring an antibody called immunoglobulin G (IgG) was highly 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, augmenting it with a test for antibodies in patients who have had symptoms for at least eight days (at which time 50 percent are producing antibodies) will help identify some positive cases that might otherwise be missed.

In another finding, researchers 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 within about two and a half months or less, on average. "We can say now that if a patient has IgA and IgM responses, they were likely infected with the virus within the last two months," conclude researchers.

Source: https://immunology.sciencemag.org/content/5/52/eabe0367
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