India will revisit Covishield dosage gap based on emerging data: Official

On the decision to increase the gap between two doses of Covishield from four-six weeks to 12-16 weeks, NTAGI chairman said the move was based on scientific data

India is considering the emerging evidence on the efficacy of partial versus full immunisation with discussions going on since mid-May on whether the country should revert to 4-8 week gaps between two doses of Covishield vaccine, said Chairman of India's Covid-19 Working Group of NTAGI, Dr N K Arora.

 These discussions started after the reports from the UK showed that a single dose of AstraZeneca, which is the same as Covishield, gave only 33 per cent protection while two doses gave 60 per cent protection. This data emerged 2-3 days after India took the decision to increase the dose gap to 12-16 weeks. 

Speaking to DD News, Arora said that Covid-19 and vaccination is a dynamic process and if a reduced gap showed benefit then it would be considered by the technical committee. “Tomorrow, if the vaccine platform tells us that a narrower interval is better for our people, even if the benefit is 5-10 per cent, 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 said.

As controversy emerged over difference of opinion regarding the decision of increased gap, the health ministry said that the call was taken in a transparent manner based on scientific data and that there was no dissent among the technical experts on the matter.

“India has a robust mechanism to evaluate data. It's unfortunate that such an important issue is being politicised!,” health minister Harsh Vardhan said in a tweet. 

Arora also quoted the studies by CMC Vellore and PGI Chandigarh showing that infection after vaccination with one dose is around 4 per cent, and around 5 per cent with two doses. “Basically, hardly any difference...Data from various sources will be integrated to assess and report on the impact of various aspects of the vaccination programme.”

India’s decision to increase Covishield gap from 6-8 to 12-16 weeks was also supported by the findings released in the last week of April, 2021 by the Public Health England, which showed vaccine efficacy varied between 65 and 88 per cent when interval is 12 weeks. 

Scientists believed that the UK was able to come out of the outbreak of the Alpha variant because of this gap. “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... This also gives flexibility to the community, since everyone cannot come at precisely 12 weeks,” Arora said. 

Canada, Sri Lanka and a few other countries are using a 12-16 week interval for the AstraZeneca vaccine.

Earlier decision of 4-week gap was based upon the bridging trial data available then, Arora said. “We felt we should increase the interval from four weeks to eight weeks, since studies showed that vaccine efficacy is about 57 per cent when it is four weeks and about 60 per cent when it is eight weeks.” 

India decided to wait for ground-level data from the UK before increasing the gap to 12 weeks. 

Government said that the recommendation of Covid-19 Working Group on increasing dose gap was taken up for discussion in the 31st meeting of the Standing Technical Sub-Committee of NTAGI, held on May 13.

This committee, chaired by Renu Swarup, secretary, Department of Biotechnology and Balram Bhargava, Director general, Indian Council of Medical Research recommended a dosing interval of minimum three months between two doses of Covishield. 

“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,” Arora said. 

He said that at the time of increasing the dose interval it was also decided that a tracking platform to assess the impact of the vaccination programme be established. This platform would assess not just the impact of the vaccination programme, but also the type of vaccine and interval between doses, and what happens when someone is fully or partially immunized. 

“This is very important in India since around 170-180 million people have received only one dose, while around 40 million people have received two doses,” Arora added.