According to a paper published in Cell, infection or natural exposure to the novel coronavirus “may prevent the recurrent episodes of severe COVID 19“. This happens as once infected with SARS-CoV-2, the immune system evokes “robust, broad and highly functional memory T cell responses”.

According to the study, the SARS-CoV-2 specific T cells are found even in the family members of people who have been exposed to the virus and have tested negative on the antibody blood test. These cells were also seen in convalescent individuals who have a history of asymptomatic COVID infection.



Strong response


All the categories of people who have recovered from moderate to severe COVID 19 infection, in the convalescent phase after mild or severe disease or exposed to family members, exhibited, “robust memory T cell responses months after infection, even in the absence of detectable circulating antibodies specific for SARS-CoV-2”, claims the study.

The scientists were able to detect the similar memory T cell response directed against the internal and surface proteins of the virus in people in whom the SARS-CoV-2 specific antibodies could not be detected.

This means that seroprevalence as an indicator may underestimate the extent of immunity in the population, say, scientists.

“The dissociation of antibodies (its absence) and a robust T cell response is noteworthy. It reinforces how much we miss by focusing on antibodies out of convenience since T cells response is only assessed in research labs,” says Research Director and Founder, Scripps Research Translational Institute,

Studies found that once infected, even the animals were fully protected from reinfection. Till date, no case of reinfection has been found in the world, whether they recovered from mild or severe COVID infection or were completely asymptomatic.

Antibodies may not be detectable in people who have mild symptoms or were completely asymptomatic. At the same time, the SARS-CoV-2 specific T cells were found in the humans that have been infected.

The study


The team of researchers characterised different T cells in 206 people including people who have recovered from moderate or severe disease and convalescent individuals and healthy blood donors.

The study was small and had limited clinical follow-ups thus it cannot be completely claimed that robust memory T cell response can protect against severe COVID 19 infection. However, the 2002 SARS and MERS induced potent memory T cell response that persists even when antibody responses wane.

When the antibodies wane with time, the robust T cell memory formed after SARS-CoV-2 infection, potent adaptive immunity is maintained, which provides protection against the severe re-infection with the virus.