In an exclusive interview with mid-day, well-known virologist Dr Jacob John from Vellore in Tamil Nadu talks about T-cells and their mandate to prove a vaccine’s efficacy, and answers other queries that continue to have diversified views among health experts. To follow up the continued efficacy of a vaccine, there is a need to test the antibody level, he said.

The T-cell became a widely discussed topic after it was missing from the Lancet study on phase 3 trials of indigenously made Covid-19 vaccine Covaxin. Later on, a non-peer reviewed study in India showed that Covaxin provides T-cell response in a human body. T-cells determine the specificity of immune response to antigens or foreign substances in the body.