NEW DELHI: The health ministry on Monday revised the interval between two doses of the
Covishield vaccine to 4-8 weeks, from the existing 4-6 weeks, after
evidence
showed higher efficacy following a longer gap between the shots.
The revised time interval between two doses is applicable only to Covishield and not to Bharat Biotech’s Covaxin vaccine. Increasing the interval between two doses is also likely to be an added advantage in covering more people as the AstraZeneca shot has been the mainstay of India’s vaccination drive.
A longer window between shots can partly address concerns that vaccinations, despite the increase in sessions, are still not proceeding fast enough. The government could focus on ensuring that as many people as possible get the first shot with a longer time-frame for the second dose.
In a letter to states and UTs, health secretary
Rajesh Bhushan
said, “Keeping the existing scientific evidence in view, it appears that protection is enhanced if the second dose of Covishield is administered between 6-8 weeks, but not later than stipulated period of 8 weeks.”
The move is based on recommendation by the National Technical Advisory Group on Immunisation (NTAGI) and by National Expert Group on Vaccine Administration for Covid-19 (NEGVAC) after reviewing the issue in accordance with the emerging scientific evidence.
“During this meeting, the recommendation has been revised to provide second dose of Covishield at 4-8 weeks’ interval after the first dose, instead of earlier practised interval of 4-6 weeks,” the ministry said.
The dosage interval of the
Oxford-AstraZeneca
vaccine, manufactured by
Serum Institute of India (SII), has been under discussion recently. The World Health Organisation’s Strategic Advisory Group of Experts on Immunisation (SAGE) had recommended an interval of 8 to 12 weeks between the doses in the light of observations that two-dose efficacy and immunogenicity increase with a longer interval. However, it also said that if the second dose is inadvertently administered less than 4 weeks after the first, it does not need to be repeated.
In February, AstraZeneca had submitted clinical trials data of its vaccine, co-developed with
Oxford University
, after requests by various regulators and authorities across the world.
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