The increase in gap between two doses of Covishield is based on scientific evidence, said chairman of COVID-19 Working Group of the National Technical Advisory Group on Immunisation (NTAGI) N.K. Arora.
In a release issued by the Union Health Ministry on his interview on DD News Dr. Arora 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 the behaviour of adenovector vaccines.
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“In the last week of April, 2021, data released by Public Health England, the United Kingdom’s executive agency of the Department of Health, showed that vaccine efficacy varied between 65% - 88% when the interval is 12 weeks. This was the basis on which they overcame their epidemic outbreak due to the Alpha variant,” he noted.
This issue was discussed and with no dissenting notes, the recommendation was that the vaccine interval had to be 12 - 16 weeks. The earlier decision of four weeks was based upon the bridging trial data available then.
Dr. Arora pointed to how emerging evidence and reports regarding the efficacy of partial vs full immunisation were being considered by the NTAGI.
“Two to three days after we took the decision to increase the dosage interval, there were reports from the U.K. that a single dose of AstraZeneca vaccine gives only 33% protection and two doses give about 60% protection; discussion has been going on since mid-May whether India should revert to four or eight weeks,” he observed. It was decided to establish a tracking platform to assess the impact of the vaccination programme.
“When the NTAGI took this decision, we also decided that India will establish a vaccine tracking platform - to assess not only the impact of the vaccination programme, but also the type of vaccine and interval between doses, and what happens when someone is fully / partially immunised. This is very important in India, since around 17 - 18 crore people have received only one dose, while around 4 crore people have received two doses,” he stated.
Two studies
Dr. Arora referred to a study by PGI Chandigarh that compared the effectiveness of partial vs full immnunisation. “A PGI Chandigarh study very clearly shows that vaccine effectiveness was 75% for both partially immunised and fully immunised. So at least in the short run, effectiveness was similar whether you are partially or fully vaccinated. This was in relation to the Alpha variant which had swept Punjab, Northern India and came to Delhi. This also meant that even if you received only one dose, still you are protected.”
Results from a CMC Vellore study were similar, he pointed out. “Few days back, another important study by CMC Vellore, Tamil Nadu, which covers most of the current epidemic wave India experienced in April and May, 2021, shows that if somebody is partially immunised, vaccine effectiveness of Covishield is 61%, and with two doses, the effectiveness is 65% - and there is very little difference, especially since there is some degree of uncertainty involved in these calculations.”
Beside the PGI and CMC Vellore studies, two other studies were coming up from two different organisations within Delhi. “And both these studies show that breakthrough infection with one dose is around 4%, and around 5% with two doses, basically hardly any difference. And the other study shows that 1.5% - 2% breakthrough infections,” he said.
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Data from various sources would be integrated to assess and report on the impact of various aspects of the vaccination programme. India had a robust system for monitoring Adverse Events Following Immunisation (AEFI), he stressed.
When asked about any proposal to reduce the Covishield gap, he said a decision would be taken scientifically, giving paramount importance to the health and protection of the community. “COVID-19 and the vaccination are very dynamic. Tomorrow, if the vaccine platform tells us that a narrower interval is better for our people, even if the benefit is 5% - 10%, the committee will take the decision on the basis of merit and its wisdom. On the other hand, if it turns out that the current decision is fine, we will continue with it.”
He emphasised that ultimately, “the health and protection given to our community is paramount. This is the most important thing which drives our discussions, generation of new scientific evidence and decision-making”.
