New Delhi, Jan. 14 -- The government's decision to administer the second dose of Covishield vaccine just four weeks after the first may lead to efficacy of just 53%, the vaccine's package insert showed. This is slightly above the cut-off of 50%, though a longer gap of at least 12 weeks would have raised the efficacy to as much as 79%.

"My view is that this 53% efficacy for two full doses given less than six weeks apart is just slightly above the threshold of 50%, but even that is not enough to meet the statistical criteria to generate enough confidence," said Davinder Gill, a vaccine expert based in Massachusetts, US.

Drugs Controller General of India (DCGI) V.G. Somani last week gave an emergency use licence to the Covishield vaccine. ...