Scientists find long-lasting immunity after mild or asymptomatic COVID-19 infection

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In a new study, researchers found evidence of protective immunity in people up to four months after mild or asymptomatic COVID-19.

They analyzed antibody and T cell responses in 136 London healthcare workers who had mild or asymptomatic COVID-19 infection dating back to March 2020.

They found that 89% of healthcare workers analyzed carried neutralizing antibodies 16-18 weeks after infection.

Even more encouragingly, in 66% of healthcare workers, they found levels of these protective antibodies are high and that this robust antibody response is complemented by T cells.

This means that if people have been infected there is a good chance that they will have developed antibodies and T cells that may provide some protection if they encounter the virus again.

The research was conducted by a team from the Queen Mary University of London and elsewhere.

From the outset of the pandemic, scientists across the globe have been working to understand how our immune system protects us against SARS-CoV-2, and how long this protection lasts.

Much of this debate around protective immunity has focussed on the different roles of B cells, which make antibodies, and T cells, white blood cells which work in several different ways to help protect from viruses, including direct killing.

In this study, the researchers found that whilst protective antibody responses were usually complemented by a T cell response, over half of the healthcare workers had mismatched antibody and T cell responses, and did not produce a T cell response specific to proteins found on the outer layer of the SARS-CoV-2 virus.

They also found that T cell responses tended to be higher in those with the classic, defining symptoms of COVID-19, while asymptomatic infection resulted in a weaker T cell immunity than symptomatic infection, but equivalent neutralizing antibody responses.

Understanding how this careful choreography of immune responses works in people with mild or asymptomatic infection is particularly important as they represent the largest infected group.

The study also provides reassurance for vaccination efforts, suggesting that even following mild infection, individuals carry antibody and T cell immunity to many parts of the virus, known as epitopes.

Whilst new variants are appearing, the changes to the virus don’t necessarily occur within these epitopes so it is hoped the vast majority of immune recognition can likely continue unperturbed.

One author of the study is Mr. Joseph Gibbons, a Postdoctoral Research Assistant at Queen Mary.

The study is published in Science Immunology.

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