Immune cells are responding to Covid six months after infection, study finds

Cellular, or “T-cell,” immunity against Covid-19 is likely to be present within most adults six months after primary infection, a new study said.

Research by the U.K. Coronavirus Immunology Consortium (UK-CIC), Public Health England and Manchester University NHS Foundation Trust has found “robust T-cell responses” to the coronavirus six months after infection.

T-cells are a part of our immune system that attack cells which have been infected with a virus or other kind of pathogen and they help other antibody-producing cells in the immune system. Scientists have been investigating T-cell responses to the coronavirus to see how lasting any immune response might be in individuals that have caught, and recovered from, Covid-19.

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

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

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 the virus, the study noted.

“T-cell responses were present in all individuals at six months after SARS-CoV-2 infection,” it said, indicating “that a robust cellular memory against the virus persists for at least six months.”

The study found, however, that “the size of T-cell response differed between individuals, being considerably (50%) higher in people who had experienced symptomatic disease at the time of infection six months previously.” The study has not yet been published or peer-reviewed.

The findings could improve our understanding of how immunity to the coronavirus works, as well as informing future vaccine strategies, the study — authored by Dr Shamez Ladhani, a consultant epidemiologist at Public Health England — noted.

“Cellular immunity is a complex but potentially very significant piece of the Covid-19 puzzle, and it’s important that more research be done in this area. However, early results show that T-cell responses may outlast the initial antibody response, which could have a significant impact on Covid vaccine development and immunity research.”

The study notes that further research is now needed to assess whether this immune response is maintained over the longer term and to better understand how the strength of the cellular immune response corresponds to the likelihood of reinfection.

Professor Paul Moss, the U.K. Coronavirus Immunology Consortium lead from the University of Birmingham, said that further work was needed to find out if people who were symptomatic with Covid-19 were safer from future reinfection.

“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.”