The head of the government’s National Technical Advisory Group on Immunization (NTAGI) said on Wednesday that the decision to increase the gap between two doses of the Covishield vaccine to 12-16 weeks was taken on the basis of “scientific evidence”.
NTAGI chair N.K. Arora’s statement came after three scientists on the panel told Reuter’s news agency the NTAGI had backed 8-12 weeks a World Health Organization recommendation. They said the body did not have data to support a switch to 12-16 weeks. Arora, however, said there was no dissent on the 12-16 week proposal amid criticism that the government increased the dosage interval to deal with the shortage of vaccines.
Arora said that in the last week of April data released by Public Health England showed that vaccine efficacy was 65-88% with a 12 weeks gap. “This was the basis on which 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,” said Arora, adding that this also gives flexibility because everyone cannot come for the second jab at precisely 12 weeks.
“Initial studies of Covishield were very heterogeneous. Some countries like the UK went for a dosing interval of 12 weeks when they introduced the vaccine, in December 2020. While we were privy to this data, when we had to decide our interval, we went for four weeks interval-based o our bridging trial data which showed a good immune response,” Arora said.
“Later we came across additional scientific and laboratory data, based on which after six weeks or so, we felt we should the interval from four weeks to eight weeks since studies showed that vaccines efficacy is about 57% when it is four weeks and 60% when it is eight weeks,” he said.
