Vaccine / Covishield single dose 61% effective against Delta, two doses 65%: COVID panel chief

New Delhi: Amid a heated debate over the required gap between the two doses of Covishield vaccine, Covid Working Group chief Dr NK Arora has said that according to research in India, a single shot had up to 61 per cent effectiveness against the Delta strain.

Here are the top 10 things you must know about the Covishield dosage gap:

The national Covid immunisation programme began with an interval of four weeks. The immune response is very good, data showed, according to Dr NK Arora. The UK, by that time, had already increased the interval to 12 weeks.

Six weeks later the WHO also suggested that 6-8 weeks interval may be a good idea. The working group, however, decided to look at the real-life data coming in from the UK, Dr Arora said.

In April, Public Health England suggested that with a 12-week interval the vaccine efficacy was varying between 65 per cent and 80 per cent. A few days later, it decided that with one Covishield dose, the protection was 33 per cent, the Working Group chairperson noted. But the number of people in the trial who got that shot was very small.

The Union Ministry of Health, on May 13, announced the decision to change the gap from 6-8 weeks to 12-16 weeks. This came at a time when supplies of the shot were falling short of demand and infections were surging across the country.

That was the second time in three months that the gap was widened. It triggered speculation it was to compensate for a shortfall in production.

The UK results, meanwhile, did not convince Dr Arora and his team. Later, statistically significant data from Christian Medical College Vellore's research, based on a sample size of several thousand during the peak Delta variant outbreak, showed that a single dose had a 61 per cent vaccine effectiveness which increased to 65 per cent with two.

In the short run, the protection from serious disease, hospitalisation, and death is similar whether one has received one dose or two doses of Covishield and Covaxin, Dr Arora said.

Dr Arora's clarification follows a Reuters report that said the Centre had doubled the gap between the two doses of Covishield without a nod from the National Technical Advisory Group on Immunisation (NTAGI) that, the government claimed, had recommended the increase.

The Reuters report quoted three scientists, including the former chief of the government-run National Institute of Epidemiology, as saying that they had only discussed increasing the interval to eight-12 weeks and not 12-16 weeks.

Union Home Minister Dr Harsh Vardhan has said the decision to increase the gap was taken in a transparent manner based on scientific data.