No dissent on 12-16 week gap on Covishield, but experts question the outer limit

The government said the NTAGI's working group on May 10 initially recommended increasing the dosing interval to 12-16 weeks

The Union Government on Wednesday asserted that its decision to expand the vaccination gap of 12-16 weeks between two doses of Covishield was taken on the basis of a unanimous recommendation of the National Technical Advisory Group on Immunisation (NTAGI), which perused available scientific information, even though a section of medical experts questioned the outer limit of 16 weeks.

There was no dissent by any member of the NTAGI and the Standing Technical Sub-Committee when it recommended a gap of three months for the second dose, the government said in a statement, countering a report that alleged three NTAGI members were against such a suggestion.

However, neither the government nor N K Arora, the chairperson of the NTAGI working group on immunisation gave any scientific explanation on imposing the outer limit of 16 weeks.

Also read: Indian scientists say they didn't back doubling of Covid-19 vaccine dose gap

Experts said there was no evidence for gains in the vaccine’s efficacy if the second dose has been delayed to 16 weeks instead of to 12 weeks or to 14 weeks. On his part, Arora said the 16 week limit was chosen due “flexibility” as everyone could not be given the jab by the 12th weeks.

“(Based on the UK experience) a decision was taken on May 13, to increase the dose interval to 12- 16 weeks. This also gives flexibility to the community, since everyone cannot come at precisely 12 weeks or so,” he added. India and the UK are the two biggest consumers of the Covishield (AZD1222).

Also read: Covishield dose interval under discussion: NTAGI working group chairman

In a subsequent NTAGI meeting on May 28, Arora pointed out Canada and Spain too had imposed a four month outer limit on the second dose of Covishield. However, no scientific study was shared on why such an outer limit was chosen.

Other experts, however, pointed out that delaying the second dose would allow more people to get the first dose, particularly at a time when vaccines are in short supply.

A recent study at the Christian Medical College, Vellore, has found that the effectiveness of Covishield is 61 per cent after one dose and 65 per cent in overall protection. The small difference, said the researcher, implied that the gains from prioritising first doses would be greater than the risks of delaying second doses.