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T cell coronavirus immunity 'present in adults six months after first infection'

 

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NIHR supported research shows robust T cell immunity is likely to be present for at least six months after asymptomatic, mild or moderate coronavirus infection. 

This study from the UK Coronavirus Immunology Consortium (UK-CIC) and Public Health England, one of the largest to date in this field, showed T cell responses in all 100 participants at six months after coronavirus (SARS-CoV-2) infection. These findings will feed not only into our understanding of how immunity to SARS-CoV-2 works but also help inform future vaccine strategies.

T cells are white blood cells that form part of our immune system and help to protect us against viruses such as SARS-CoV-2 (the virus that causes COVID-19). They can do this by acting as ‘killer cells’ to destroy virus-infected cells, or they can act as ‘helper cells’ which support B cells to produce antibodies. 

As part of UK-CIC, jointly funded by NIHR and UK Research and Innovation, researchers from the University of Birmingham, Public Health England and NIHR Manchester Clinical Research Facility collected blood samples from a cohort of more than 2,000 healthcare workers, including 100 individuals who tested positive for SARS-CoV-2 in March and April 2020. 

All 100 individuals experienced either mild or moderate symptoms, or were asymptomatic, and none were hospitalised for COVID-19. Blood samples were collected monthly to measure antibody levels, and again after six months to assess the T cell (cellular) response. 

A range of analyses were carried out to assess different aspects of the T cell response, including the magnitude of response and the response to different proteins from SARS-CoV-2. The T cell response was measured against a range of proteins from the virus, including the Spike protein that is being used in most vaccine studies. 

The researchers found that the size of T cell response was 50% higher in people who had experienced symptomatic disease at the time of infection six months previously. The results are published in a bioRxiv pre-print, which reports preliminary data that has not yet been peer reviewed.

It is possible that heightened T cell immunity might provide increased protection against re-infection in people with initial symptomatic infection, or that asymptomatic individuals are simply able to fight off the virus without the need to generate a large immune response.

Professor Paul Moss, UK Coronavirus Immunology Consortium lead from University of Birmingham, said: “To our knowledge, our study is the first in the world to show robust cellular immunity remains at six months after infection in individuals who experienced either mild/moderate or asymptomatic COVID-19.

“Interestingly, we found that cellular immunity is stronger at this time point in those people who had symptomatic infection compared with asymptomatic cases. We now need more research to find out if symptomatic individuals are better protected against reinfection in the future.”

Further research is needed to assess whether this immune response is maintained over the longer term and to better understand how strength of cellular immune response relates to likelihood of reinfection. 

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