The T-cell study adds to the debate about the duration of...

A small UK study found that people with mild or asymptomatic COVID-19 infections have “cellular immunity” to the pandemic SARS-CoV-2 virus after six months – suggesting that they will have one for at least that period could have some protection.

A woman with a face mask will take part in the weekly “Clap for our Carers” in front of the Houses of Parliament in London for the last time on May 28th. Photo: Xinhua

Scientists presenting the results of 100 unhospitalized COVID-19 patients in the UK said they were “comforting” but did not mean that in rare cases, people cannot become infected twice with the disease.

“While our results lead us to be cautiously optimistic about the strength and duration of immunity generated after SARS-CoV-2 infection, this is only part of the puzzle,” said Paul Moss, professor of hematology at the UK University of Birmingham-led the study.

“There’s still a lot to learn before we have a full understanding of how immunity to COVID-19 works.”

The study, which has not yet been peer-reviewed but has been published online on bioRvix, analyzed the blood of 100 patients six months after those patients had either mild or asymptomatic COVID-19.

It found that while some of the patients’ antibody levels had decreased, their T-cell response – another important part of the immune system – remained robust.

„“[Our] Initial results show that T cell responses can outlast the initial antibody response, “said Shamez Ladhani, a consultant epidemiologist at Public Health England who helped lead the work.

The study also found that the size of the T cell response varied and was significantly higher in people with symptomatic COVID-19 than in people who had no symptoms when infected.

The researchers said this could be interpreted in two ways: it is possible that higher cellular immunity offers better protection against re-infection in people with symptoms, or that asymptomatic patients are better able to fight off the virus without it being generated needs a great immune response.

Experts not directly involved in the study said their results were important and would add to a growing knowledge of possible protective immunity to COVID-19.

“These results give certainty that although the titer of the antibody to SARS-CoV-2 can fall below detectable levels within a few months after infection, a certain level of immunity to the virus can be maintained,” said Charles Bangham, Department of Immunology at Imperial College London.

“The crucial question, however, remains: do these persistent T cells offer effective protection against renewed infection?”

While more than 46 million people have been infected with COVID-19 worldwide, confirmed cases of reinfection are so far very rare.