The government-approved gap between the first and the second dose of Serum Institute of India’s Covishield vaccine has been protracted to up to eight weeks from up to six weeks earlier.

The conclusion was based on a commendation by the National Technical Advisory Group on Immunization (NTAGI) and successively the National Expert Group on Vaccine Administration for COVID-19 (NEGVAC). The two groups made the recommendation after the NTAGI saw the available data from AstraZeneca and Oxford’s clinical trials for the vaccine in the UK and Brazil, as well as Serum Institute’s own bridging study in India. The data showed that protection provided by Covishield is enhanced if the second dose is administered between 6-8 weeks, but not so if it was more than eight weeks.

The panels’ recommendation follows a new analysis of interim usefulness data by AstraZeneca in February, which showed that the vaccine’s efficacy increased from 54.9% to 59.9% if the interval between first and second dose was increased from less than 6 weeks to 6-8 weeks. The two most prominent references for the AstraZeneca vaccine and Covishield are from the UK Medicines and Healthcare Products Regulatory Agency and the World Health Organization (WHO). India’s decision varies from the two. While the UK MHRA suggests a 4-12 week interval, the WHO has suggested an 8-12 week interval.

It looks like the biggest benefit of the longer interval will be that it would free up doses for people to get their first Covishield shot, which in turn will allow the government to include a much larger proportion of the population in its covid immunization programme.

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Joydev Mishra


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