4-week gap for second Covishield dose could lower its efficacy: Report

As the country is set to begin a massive anti-coronavirus inoculation drive from January 16, a new concern is looming over the efficacy of Covishield vaccine if the second dose is administered after four weeks.

Experts fear that the government’s decision to administer the second dose of Serum Institute's Covishield vaccine just four weeks after the first may lower the efficacy of just 53 per cent. A long gap of 12 years would have raised the efficacy to nearly 79 per cent, according to a report by Mint.

The vaccine experts are worried that “just 53 per cent efficacy” would not be enough to meet the statistical criteria to generate enough confidence.

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

The expert committee set up by the DCGI had recommended that the second dose should be administered between four and six weeks after the first dose. It also acknowledged that there was data available for administration of the second dose up to 12 weeks.

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According to the report, the efficacy of the vaccine would be 53.28 per cent if the second shot was given at an interval of fewer than six weeks and 51.08 per cent if it was given between six to eight weeks. The report suggested that the results were of poor statistical significance due to the small sampling size.

Defending the data during the trials, Serum Institute of India's executive director Prasad Kulkarni had told the publication that based on its results in UK and Brazil trial, the vaccine had an efficacy rate of 70 per cent, irrespective of the dosing interval. Gill also informed that increasing interval between dosages would lead to complications in a pandemic situation. “Even the vaccines might not remember three months later that they have to take a second dose,” he said.

Meanwhile, all 1.65 crore doses of Covid-19 vaccines -- 1.1 crore of Covishield and 55 lakh of Covaxin -- procured by the Centre have been allocated to all states and UTs in proportion to their healthcare workers’ database, and over 3 lakh workers are set to get their first Covid-19 vaccination on the first day of inoculation drive.