Dr N K Arora Chairman of India’s COVID-19 Working Group of the National Technical Advisory Group on Immunisation (NTAGI), Dr. N K Arora, spoke to DD News and explained that the decision to increase the gap between two COVISHIELD doses from 4-6 weeks to 12 – 16 weeks lay in the fundamental scientific reason regarding behaviour of adenovector vaccines.
“In the last week of April, 2021 the data released by Public Health England, United Kingdom’s executive agency of the Department of Health, showed that vaccine efficacy varied between 65% – 88% when interval is 12 weeks. This was the basis on which they overcame their epidemic outbreak due to the Alpha variant. The UK was able to come out of it because the interval they kept was 12 weeks. We also thought that this is a good idea, since there are fundamental scientific reasons to show that when interval is increased, adenovector vaccines give better response. Hence the decision was taken on May 13, to increase the interval to 12 – 16 weeks.” This also gives flexibility to the community, since everyone cannot come at precisely 12 weeks or so, he added.
He empathically highlighted the fact that the decision to increase the gap between two doses of Covishield vaccine was taken based on scientific evidence.
Dr Arora said that the earlier decision of four weeks was based upon the bridging trial data available then. He also cited that the increase in gap between two doses was based on studies that showed higher efficacy with increase in gap.
Speaking about why the NTAGI did not increase the gap earlier to 12 weeks, he said, “We decided we should wait for ground-level data from the UK (the other biggest user of AstraZeneca vaccine).”
He also said that there were other examples like Canada, Sri Lanka and few other countries which are using 12 – 16 weeks interval for AstraZeneca vaccine which is the same as COVISHIELD vaccine.