‘Antibodies more important than T-cells in long-term’

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.

Dr Jacob John, virologist

Some experts say vaccinated individuals need follow-ups up to 18-24 months and even more to make sense of T-cells to ascertain a vaccine's efficacy. What is your view?
There is no need to routinely check T-cell immunity in vaccinated people. Usually T-cell immunity, once induced, is long lasting. However, to follow up the continued efficacy of a vaccine, an antibody test is required. Two-dose recipients show waning of immunity (drop in antibody levels) from about six months to a year. What ought to be done is to offer a booster dose, instead of monitoring the antibody level and administering the booster shot when it drops. That is not practical. I strongly recommend a booster dose routinely.

Fully vaccinated people in Europe, US and other nations are still getting Covid-19. Why?
The short vaccination schedule of two doses will not induce strong immunity to prevent SARS-CoV-2 [virus that causes Covid-19) infection, for which a booster dose is necessary. Thereafter, probably no more booster shots may be necessary for a few years. But, that can be clarified only by future studies.

When we spoke last about T-cells being an important parameter for a Covid-19 vaccine, you said that is ‘book knowledge'. A new study shows Covaxin has better T-cell response compared to antibodies. What is your opinion?
Demanding T-cell immunity in the publication on phase 3 vaccine trial was what I called book knowledge. Lancet editors did not ask for it, because it is not normally required in phase 3 trial reports. Reduction of risk of the disease, in quantified data and vaccinated versus placebo recipients is normal. I said that T-cell immunity studies had been done and reported in phases 1 and 2 trials.

Do you think T-cells study is needed for all Covid-19 vaccines globally?
All of them have T-cell immunity data from phase 1 and phase 2 reports. All European/US vaccines and Covaxin had been reported to induce T-cell immunity. Some Chinese vaccines had only antibody studies, as far as I recall. Demanding T-cell immunity studies on a large scale is not a sign of practical knowledge of the rules of the game.

Out of the 10 Covid-19 vaccines available globally, which one is better?
All vaccines approved by the respective national regulatory agencies are "safe and effective", but there are both safety and efficacy issues on most of them. Two-dose efficacy seems highest for the two mRNA vaccines. Covaxin seems to be the safest among all vaccines.

There are reports of life-threatening blood clot incidents in AstraZeneca (Covishield in India) vaccine. Anaphylaxis (life-threatening allergic reaction) seems to be a bit more common for Pfizer vaccine than Moderna, and it seems to be higher for the both than in AstraZeneca ‘s. It seems to be the least for Covaxin. Vaccines with WHO blessing (emergency use authorisation) are on top of the list for assured safety and efficacy. There are just six such vaccines now, including Covaxin.