Covishield - developed by AstraZeneca-Oxford University - is produced by the Serum Institute (File)
The decision to increase the gap between two doses of the Covishield vaccine was "transparent" and "based on scientific data", Union Health Minister Dr Harsh Vardhan tweeted Wednesday.
This is amid concern the intervals were widened - from six-eight weeks to 12-16 - without the support of the scientific group the government said had recommended the decision with "no dissenting voice".
"The decision to increase the gap between administering two doses of Covishield has been taken in a transparent manner based on scientific data. India has a robust mechanism to evaluate data. It is unfortunate that such an important issue is being politicised!" the Health Minister tweeted.
He attached a statement from the government that extensively quoted Dr NK Arora, the chief of the National Technical Advisory Group on Immunisation (NTAGI), on the subject.
In the statement Dr Arora was quoted citing a study by UK health regulator Public Health England that "showed vaccine efficacy varied between 65 per cent - 88 per cent when interval is 12 weeks".
"This was the basis on which they overcame the outbreak due to the 'alpha' variant... because the interval they kept was 12 weeks. We also thought that this is a good idea... scientific reasons to show that when interval is increased adenovector vaccines give better response," he was quoted.
"The COVID Working Group took that decision with no dissenting voice.... issue was then discussed threadbare at an NTAGI meeting, again with no dissenting notes. The recommendation was that the vaccine interval has to be 12 - 16 weeks," he was further quoted.
However, a report by news agency Reuters quotes three scientists, including MD Gupte - the former Director of the government-run National Institute of Epidemiology - as saying they only discussed increasing the interval to eight-12 weeks.
"Eight to 12 weeks is something we all accepted, 12 to 16 weeks is something the government has come out with," he said, adding, "This may be alright, may not be. We have no information."
This was echoed by his NTAGI colleague Mathew Varghese, who said the group's recommendation was only for 8-12 weeks.
The NTAGI did not specifically discuss a 12-16 week interval, JP Muliyil, another member, added.
Reuters said Dr Arora declined to comment on their report, but said all decisions were collective.
In mid-May the government cited "available real-life evidence, particularly from the United Kingdom" to increase the intervals.
That was the second time in three months the gap was widened, and it triggered speculation it was to compensate for a shortfall in production.
Widening of Covishield dosage intervals has been linked to increased efficacy.
But the timing sparked suggestions the government was trying to eke out limited stock available at the time and give as many people as possible at least one dose till supply could be replenished.
Last week Dr Anthony Fauci, the medical advisor to the United States President, told NDTV that extending intervals could leave people vulnerable to newer, and more aggressive strains.
However, he also said it may be necessary "if you have a very small supply".
Vaccine supplies became an issue as the country was hit by a devastating second wave of infections, with states shutting centres due to a lack of doses. The government hit back, saying they did, in fact, have enough to inoculate people, and accused state governments of wasting doses.
The government plans to vaccinate all eligible beneficiaries - around 108 crore - by end-2021, and, last month, a top advisor said over 200 crore doses will likely be available between August-December.
With input from Reuters