New Evidence of Protective Immunity After COVID-19 Infection Gives Hope for Long-Lasting Vaccine Efficacy

New research has found evidence of protective immunity in people up to four months after mild or asymptomatic COVID-19, raising hopes that a vaccine could offer long lasting efficacy.

In a study, scientists from the Queen Mary University of London (London, UK) analyzed antibody and T cell responses in 136 London healthcare workers who had mild or asymptomatic COVID-19 infection dating back to March 2020. The scientists found that 89% of healthcare workers analyzed carried neutralizing antibodies 16-18 weeks after infection. They found most also had T cells capable of recognizing multiple different parts of the virus, however the two responses did not always persist in harmony, with some individuals showing T cell immunity but no evidence of antibodies, and vice versa.

In their study, the researchers showed that while 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 new 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. While 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.

“Our study of SARS-CoV-2 infection in healthcare workers from London hospitals reveals that four months after infection, around 90% of individuals have antibodies that block the virus,” said Joseph Gibbons, a Postdoctoral Research Assistant at Queen Mary. “Even more encouragingly, in 66% of healthcare workers we see levels of these protective antibodies are high and that this robust antibody response is complemented by T cells which we see reacting to various parts of the virus. This is good news. It means that if you have been infected there is a good chance that you will have developed antibodies and T cells that may provide some protection if you encounter the virus again.”

“Our study in asymptomatic and mild cases gives a positive insight into the durability of immunity to SARS-CoV-2 after four months of infection,” said Dr. Corinna Pade, a Postdoctoral Research Scientist at Queen Mary. “A remarkable number of around 90% of individuals have a joint force of strong antibodies that prevent the virus from entering, coupled with T cell responses to various parts of the virus to interfere with its survival. This is an important find as mild or even no symptoms of COVID-19 are very common and representative of most infections in the community. Such abundant immune responses also give hope for the long-lasting efficacy of vaccines.”


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Queen Mary University of London