ET Explains: Why did India extend the gap between Covishield vaccine doses?

India today announced that the gap between doses of Covishield vaccine would be extended to up to eight weeks. Covishield, the Oxford-AstraZeneca vaccine, is made in India by the Serum Institute and is supplied to many places across the world.

Why the change
The decision was announced after an expert panel backed such a course of action.


The National Technical Advisory Group on Immunisation had arrived at its decision in a meeting last week. At the meeting, "strong scientific rationale was presented" that a 4-8 week is most suitable for Indians.

A Lancet report early this month had showed that a longer gap before the second shot makes for a higher efficacy rate (as much as 90%), compared to if given after 4-6 weeks of the first.

What did the research exactly find?
Studies on Covishield showed that a gap of 6-12 weeks after the first dose is likely to make the booster dose more effective.

The Health Ministry said that "protection is enhanced if the second dose of Covishield is administered between 6-8 weeks, but not later than stipulated period of 8 weeks."

What is the current practice?
The existing gap between doses being followed in India is 4-6 weeks.

Will the newly mandated gap be applicable to all vaccines?
No, this will only be applicable to Covishield. For Covaxin, the one made by Bharat Biotech, the existing gap between doses (4-6 weeks) will continue to apply.

Have others done such extensions as well?
UK and Canada, who are among the countries administering Covishield to their citizens, have expanded the gap to four months.

What does the WHO recommend?
The World Health Organisation (WHO) recommends a six-week interval between the doses.

Covishield was approved for emergency use by the Drugs Controller General of India in January. According to media reports yesterday, the Central government has ordered 12 crore more shots — 10 crore Covishield and the rest Covaxin — from Serum Institute and Bharat Biotech.

Meanwhile, urgent missives have been sent to the States and United Territories to follow the revised dosing regimen.