The Indian government doubled the gap between the two doses of the AstraZeneca Covid-19 vaccine without the agreement of the scientific group that it said recommended the increase, three members of the advisory body told Reuters.

The Union health ministry had announced the decision to change the gap between doses of Covishield, the AstraZeneca vaccine manufactured by the Serum Institute of India, from six-eight weeks to 12-16 weeks on May 13, at a time when supplies of the shot were falling short of demand and infections were surging across the country.

The ministry said the extended gap was recommended by the National Technical Advisory Group on Immunisation (NTAGI), based on real-life evidence mainly from the UK. Yet the NTAGI scientists, classified by the government as three of the 14 “core members”, said the body did not have enough data to make such a recommendation.

M.D. Gupte, a former director of the state-run National Institute of Epidemiology, said the NTAGI had backed increasing the dosing interval to 8-12 weeks — the gap advised by the World Health Organisation. But he added that the group had no data concerning the effects of a gap beyond 12 weeks.

“Eight to 12 weeks is something we all accepted, 12 to 16 weeks is something the government has come out with,” he added. “This may be all right, may not be. We have no information on that.”

This was echoed by his NTAGI colleague Mathew Varghese, who said the group’s recommendation was only for eight to 12 weeks.

The health ministry, citing the head of NTAGI’s working group on Covid-19, said the dosing decision was based on scientific evidence. “There was no dissenting voices among the NTAGI members,” it tweeted on Tuesday.

The ministry’s statement on May 13 said that it had accepted the 12-16 weeks’ recommendation from NTAGI’s Covid working group, as had a group of mainly government officials tasked with vaccine administration, known as NEGVAC (National Expert Group for Vaccine Administration of Covid-19).

Government health officials told a news meet on May 15 the gap was not increased to address a vaccine shortage but was a “scientific decision”.

J.P. Muliyil, a member of the seven-strong Covid working group, said there had been discussions within the NTAGI on increasing the vaccine dosage interval but that the body had not recommended 12-16 weeks. “That specific number was not quoted,” he said, without elaborating.

N.K. Arora, head of the Covid working group, declined to comment on its recommendations but said all decisions were taken collectively by the NTAGI at large.

A NEGVAC representative said it “respects the decisions of the NTAGI and use them for our work”, declining to elaborate.