Single Dose Of Covishield 61% Effective; Will Revisit Vaccine Interval With Fresh Data: NTAGI Chief

"Tomorrow, if the vaccine platform tells us that a narrower interval is better for our people, even if the benefit is 5-10%, the Committee will take the decision on the basis of merit and its wisdom," said Dr. NK Arora

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New Delhi: A single dose of Covishield is 61% effective on the 'Delta' variant noted Dr. NK Arora, who is the expert chairman National Technical Advisory Group on Immunisation (NTAGI). About the ongoing debate on the vaccine interval, he said that the group will review new data and make their decision based on that. 

On the decision to increase the gap between two doses of Covishield from four-six weeks to 12-16 weeks, he said the move was based on scientific decision and there was no dissenting voice among the National Technical Advisory Group on Immunisation (NTAGI) members.

“COVID-19 and the vaccination are very dynamic. Tomorrow, if the vaccine platform tells us that a narrower interval is better for our people, even if the benefit is 5-10%, the Committee will take the decision on the basis of merit and its wisdom. On the other hand, if it turns out that the current decision is fine, we will continue with it,” Arora said. 

Arora explained that the basis for increasing the interval between vaccine doses was the basic scientific reason for "adenovector vaccines". The UK's Department of Health's agency 'Public Health England' released data in the last week of April and said that when there is a 12-week interval between doses of the vaccine, its effectiveness is between 65 and 88 percent. 

“This was the basis on which they overcame their epidemic outbreak due to the Alpha variant. The UK was able to come out of it because the interval they kept was 12 weeks. We also thought that this is a good idea since there are fundamental scientific reasons to show that when the interval is increased, adenovector vaccines give a better response. Hence the decision was taken on May 13, to increase the interval to 12-16 weeks,” he said.

“While we were privy to this data, when we had to decide our interval, we went for four weeks interval based on our bridging trial data which showed a good immune response. Later we came across additional scientific and laboratory data, based on which after six weeks or so, we felt we should increase the interval from four weeks to eight weeks since studies showed that vaccine efficacy is about 57 percent when it is four weeks and about 60% when it is eight weeks, he said.

On why the NTAGI did not increase the gap earlier to 12 weeks, he said, “We decided we should wait for ground-level data from the UK (the other biggest user of AstraZeneca vaccine).” He also said that there were other examples like Canada, Sri Lanka and few other countries which are using 12-16 weeks interval for AstraZeneca vaccine which is the same as Covishield vaccine, the statement said.

On the protection from single-dose versus two doses, Arora explained how emerging evidence and reports regarding the efficacy of partial versus full immunization were being considered by NTAGI.

Arora referred to a study by PGI Chandigarh which compared the effectiveness of partial versus full immunization. A PGI Chandigarh study very clearly shows that vaccine effectiveness was 75 percent for both partially immunized and fully immunized. So at least in the short run, effectiveness was similar whether you are partially or fully vaccinated. This was in relation to the Alpha variant which had swept Punjab, north India, and came to Delhi. This also meant that even if you received only one dose, still you are protected.