NEW DELHI: A study from India that may have implications for Covid-19 vaccines has reported long-term persistent immune T-cell memory responses in patients with mild coronavirus and even “pre-existing” immunity in those yet unexposed to the disease.
The pre-existing immunity in people unexposed to SARS-CoV-2 comes from cross-reactivity with certain common cold viruses.
This had been first reported by Singapore, then by US doctors.
Now, researchers associated with the National Institute of Immunology and AllMS, Delhi, along with scientists from the US have confirmed this in India at higher levels than observed in those countries.
In India, 70% of the sample of unexposed people had cross-reactive immunity compared with 45% in Singapore and 50% in the US.
The doctors in the paper — “Immune memory in mild Covid-19 patients and unexposed donors from India reveals persistent T cell responses after SARS-CoV-2 infection” — have speculated that this high pre-existing cross-reactivity could be one reason for India’s low case fatality rates.
“By providing the knowledge on cellular immune responses to SARS-CoV-2, our work has implications for the evaluation and implementation of vaccines against Covid-19,” the authors have noted.
To investigate the quality and stability of immune reactivity in the Covid patients, researchers recruited 28 adult patients who had recovered from mild coronavirus and followed them over five months.
They have now reported that significant titers of antibodies and memory cells after several months post-infection indicate persistent antibody response in mild disease.
“Our observation is consistent with the recent reports where no decline was observed in antibodies to SARS-CoV-2 within 4 to 5 months of the COVID-19 diagnosis,” they have said. Despite high burden of the Covid-19 incidences; the case fatality rates in Indian contingent are extremely low, said the researchers, adding that whether the high magnitude of cross-reactive CD4+ T cells (memory immunity cells) are contributing to this less severe outcome needs to be addressed.