We also know that critically ill patients experience an increase in inflammation factors (inflammatory cytokines) and immune system overreaction, whereas the number of T cells, the "command centers" for immune cells, is significantly reduced in the blood. "T cell memory might reach a more stable plateau, or slower decay phase, later than the first 6 months post-infection", the study states. Like many countries in Europe, Spain is facing a second wave of coronavirus infections which is putting pressure on the country's health services.
A study published Friday by Oxford University ensures that people infected with coronavirus have little chance of returning to the disease in at least six months.
They found that while T cells were markedly activated in the lungs of patients with severe pneumonia, the T cell braking function stopped working.
Until now much of scientists' attention has been focused on antibodies, which neutralise a virus before it enters the body's cells. To shed light on the problem, a research collaboration based in Kumamoto University (Japan) has performed a genetic analysis of T cells from lung tissue of COVID-19 patients.
Staff with antibodies were also less likely to test positive for COVID-19 without symptoms, the researchers said, with 76 without antibodies testing positive, compared to only three with antibodies.
The British healthcare workers did the study on the frontline of the battle against the coronavirus. One theory is that antibodies fade very quickly after someone recovers from Covid - but T-cells are longer lasting.
"But this latest study shows that there is some immunity in those who have been infected".
But Dr Wrighton-Smith added: 'We are not picking up all cases with the antibody surveys - so more people may be protected than we thought'.
The research suggested COVID-19 immunity may last for years.
"It gives us hope that immunity to SARS-CoV-2 could last for several years", said Prof Deborah Dunn-Walters, Professor of Immunology at University of Surrey and Chair of the British Society for Immunology expert advisory group on covid-19 Immunology.
But Dr Rupert Beale of the Francis Crick Institute in London, said the issue may be to do with the antibody tests used.
Local health officials in every part of the state have investigated outbreaks that started with get-togethers that seemed innocent at the time, but led to many people getting sick, and in some cases, hospitalizations and deaths.