Based on examine outcomes, immune cells reply to Covid-19 six months after an infection

A doctor applies a nasal swab during testing at the Orange County Health Services Covid-19 transit point in Barnett Park in Orlando, Florida on Thursday, October 29, 2020.

Joe Burbank | Tribune News Service | Getty Images

According to a new study, most adults are likely to have cellular or "T-cell" immunity to Covid-19 six months after initial infection.

Research by the British Coronavirus Immunology Consortium (UK-CIC), Public Health England and the NHS Foundation Trust of the University of Manchester have shown "robust T-cell responses" to the coronavirus virus six months after infection.

T cells are part of our immune system that attack cells that have been infected with a virus or other type of pathogen. Scientists have studied T cell responses to the coronavirus to determine how long an immune response lasts in people who have caught Covid-19 and are recovering from it.

This latest study looked at 100 people who tested positive for the coronavirus in March and April 2020 but had not been hospitalized with the virus. All 100 people had either mild or moderate symptoms, or were asymptomatic (56 versus 44 people), according to the study.

Serum samples were collected monthly to measure antibody levels and after six months blood samples were taken to assess cellular (T cell) response to the virus.

A number of analyzes were performed to assess various aspects of the T cell response, including the magnitude of the response and the response to different proteins in the virus, the study said.

"T-cell responses were present in all subjects six months after SARS-CoV-2 infection," it says, "which indicates that a robust cellular memory against the virus lasts for at least six months."

However, the study found that "the size of the T-cell response varied between individuals and was significantly (50%) higher in people who had symptomatic disease at the time of infection six months earlier". The study has not yet been published or peer-reviewed.

Part of the Covid-19 puzzle

The results could improve our understanding of how immunity to the coronavirus works and inform future vaccination strategies, according to the study, led by Dr. Shamez Ladhani, an epidemiologist consultant with Public Health England.

"Cellular immunity is a complex but potentially very important piece of the Covid-19 puzzle and it is important that more research be done in this area. However, initial results show that T cell responses can outlast the initial antibody response that could have had a significant impact on Covid vaccine development and immunity research. "

The study notes that more research is now needed to determine whether this immune response is sustained over the longer term and to better understand how the strength of the cellular immune response corresponds to the likelihood of re-infection.

Professor Paul Moss, head of the University of Birmingham's UK Coronavirus Immunology Consortium, said more work was needed to determine whether people who were symptomatic with Covid-19 are safer from future reinfection.

"Interestingly, we found that cellular immunity at this point in time is stronger in people with symptomatic infection compared to asymptomatic cases. We now need to investigate more closely whether symptomatic people are better protected against re-infection in the future."

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