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Explained: Should the gap between Covid-19 vaccine doses be stretched?

Covid-19 vaccine: In the wake of global studies, several scientists have called for stretching the interval between the two doses to up to three months.

Written by Anuradha Mascarenhas | Pune |
Updated: March 2, 2021 2:35:44 pm
A vaccine for Covid-19 is administered to an elderly person, in Delhi on Monday (Express Photo: Praveen Khanna)

In India’s vaccination programme, the prescribed interval between the two doses of Covishield is 28 days. In the wake of global studies, several scientists have called for stretching the interval to up to three months.

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The India regimen

Regulatory studies in the country have said the interval should be four to six weeks. These findings are based on Phase 3 studies.

Till date, India’s vaccination coverage has crossed 1.43 crore. Of 66.69 lakh healthcare workers who have received the first dose, 24.56 lakh have got the second and final jab. The second dose started on February 13 for those who had completed 28 days after the first dose.

Global findings

The WHO’s advisory group SAGE on February 10 suggested an 8-12-week interval between doses. And on February 19, The Lancet published results of a study that showed a three-month interval between doses of the Oxford-AstraZeneca vaccine results in higher efficacy than with a six-week interval, with the first dose offering 76% protection in the three months between doses. Covishield is a version of the Oxford-AstraZeneca vaccine.

“The cumulation of evidence around the world shows there is 20% to 30% greater efficacy by stretching the interval between two doses. So why would we not want to do that,” leading vaccine scientist Dr Gagandeep Kang told The Indian Express.

Oxford Professor Andrew Pollard, lead author of the study in The Lancet, has said: “Where there is a limited supply , policies of initially vaccinating more people with a single dose may provide greater immediate population protection than vaccinating half the number of people with two doses.”

To stretch interval…

“The government should very seriously consider this. A 20% increase in efficacy when you give it to millions of people is tens of thousands of new infections prevented . You can give more doses to more people, export vaccines to more places. Yes , Covid infections are showing a rise but we need to plan. Where there is little disease one can stretch the interval of doses,” Dr Kang said.

“There is ample evidence from the Lancet paper that one gets pretty good short-term protection from the first dose,” she said.

Scientists at Serum Institute of India (the Covishield manufacturer) also noted that the longer the interval between doses, the better the protection observed, and it happens with all vaccines.

Dr Shashank Joshi, expert on Maharashtra’s Covid-19 task force, noted that several doubts have been raised about the interval. “A gap of four weeks is reasonable but ideally the 8-12 weeks is better. Recent data suggests that the immune response is better with a gap of 8-12 weeks as adopted by the UK government. The Indian government may also implement this strategy,” Dr Joshi said.

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… Or not to

Prof Sanjay Rai, president of Indian Public Health Association, said the vaccine is precious and there is a need for judicious use. He said clinical trials were the best evidence and had more weightage than observational studies, and felt it was better to give both doses within the time frame laid down by the Centre’s drug regulator until such time that more robust evidence can be generated.

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