As newer vaccines emerge, bridging trials divide the scientific community

Are vaccine-makers hesitant in undertaking bridging studies in India on vaccines developed overseas?

While some vaccine-makers keep their cards close to the chest, the scientific community is divided in its opinion on the need for such a trial, especially when the vaccine has received the regulatory go-ahead from a regulator like the United States Food and Drug Administration, for instance.

Presently, three foreign vaccines from AstraZeneca-Oxford University, Novavax and Gamaleya Institute’s Sputnik V have done or are undertaking local trials, through Serum Institute (for the first two) and Dr Reddy’s Laboratories, in the case of the last vaccine.

The other two vaccines of interest to India are from Pfizer, which applied for an emergency authorisation, but withdrew it, as additional data was sought. And more recently, Johnson and Johnson’s one-dose vaccine has just been approved in the US. J&J has a production alliance in India through Biological E, and a highly-placed source told BusinessLine that the company had sought no applications or waivers.

Regulatory officials and clinical researchers, on conditions of anonymity, say that bridging trials are required to understand how a vaccine works on the local population, as there are issues of ethnicity and so on. Besides, adds a researcher, the need for fast-track and seek a waiver makes sense early in the pandemic.

Presently, India appears to be comfortable with two vaccines being rolled out from Bharat Biotech and Serum Institute, and the Covid-19-linked mortality is less than the United States, for instance. So there is no compelling case to pedal back on the bridging study, he said. Besides, the expectation is that a third vaccine is close to getting approvals in the country (the reference being to Sputnik V).

Every country does what is good in its citizens' interest, he adds, pointing to the US taking its time on approving the AZ-Oxford vaccine. And this, even as Britain was the first off the block in authorising a vaccine from Pfizer.

Striking a contrarian note, vaccine expert Dr Vipin Vashishtha points out that a bridging trial was not required on a vaccine that has received regulatory approvals elsewhere. Such a study gives the immunogenicity levels or the level of antibodies created to protect a person, he points out. Some of the later vaccines have done global trials in a diverse population. In countries like South Africa that had variants of the virus, he says, indicating that authorities can go with the data from a vaccine tested against such challenges.

Another expert watching the developments adds that the regulatory requirement is not cast in stone, and the Government should take a nuanced approach. So while the country appears to be comfortable, he said, the vaccine maker may have a case for a waiver if the vaccine was seen to be effective against multiple variants. But broadly, bridging trials are required given local population and genetic variations, he added.