India is following the successful strategy of the UK in extending the time gap between two doses of the Covishield (AstraZeneca-Oxford) vaccine to 12-16 weeks, AIIMS, Delhi chief Dr Randeep Guleria said on Saturday.

Explaining the reasoning behind the move, he said,  "The data which emerged on the basis of mathematical modelling suggested that if you took the Covishield vaccine in less than four weeks time or around the fourth week, your immunity was around 55 to 60 per cent but if you took the shot after 12 weeks, the immunity ends up at around 80 to 85 per cent.

“This has prompted the regulators to recommend that the Covishield vaccine could be taken later than earlier that is why the duration for the second dose has been extended to 12 to 16 weeks," Guleria said while briefing the nation on the vaccine strategy. 

UK’s AstraZeneca vaccine is being manufactured at the Serum Institute of India at Pune under the Covishield brand name.

Dr Gueria also said, "When there was this huge surge in the United Kingdom in November-December last year, they took a calculated risk and decided to extend the second dose duration up to 12 weeks. That seemed to have worked and this was seen as a successful strategy as far as both the AstraZeneca and Pfizer vaccines are concerned because they were able to vaccinate more people."

He further explained that studies published in the reputed UK medical journal The Lancet suggest that people who took a single dose of the vaccine had around 70 to 75 per cent of protection.

"Now that is not ideal as we would like to have as high a percentage of protection as possible, because that would mean there would be still around 2 to 30 per cent of people who will get infection even after having the one shot of the vaccine. However, looking from the public health point of view, looking at the huge surge of cases that seems to be acceptable as a good number," he said.

Dr Guleria further stated that India is preparing to ramp up the vaccination drive as more vaccines will become available in India in the next two months.

While jointly briefing the nation on the vaccination plan Dr Guleria stated that the elderly should be vaccinated at the earliest, looking at their comorbidities and their high mortality rate.

The AIIMS chief came out in favour of a strategy where appointments for vaccination could be given two, three or four months later for the younger age group.