The US regulatory authority has declined to evaluate Covaxin, India’s homegrown Covid-19 vaccine, under the emergency use authorisation (EUA) pathway and recommended an alternative route that would require an additional clinical trial.

The US Food and Drug Administration (FDA) has recommended that Ocugen — the US partner of vaccine maker Bharat Biotech — pursue a biologics licence application (BLA) instead of EUA and requested additional information and data, the companies said.

Data from an additional clinical trial would be required to support submissions for the approval under the BLA route, the companies said, adding that the process would take longer than it would have under the fast-tracked EUA pathway.

“While this will extend our timelines, we are committed to bringing Covaxin to the US,” Shankar Munsunuri, chief executive officer of Ocugen, said in a statement. “This differentiated vaccine is a critical tool to include in our national arsenal given its potential to address SARS-CoV-2 variants.”

Bharat Biotech has already conducted a clinical trial of Covaxin in India involving 25,800 volunteers that, the company has said, has shown an efficacy of 78 per cent in protecting people from Covid-19 and 100 per cent efficacy against severe disease.

The FDA’s decision to recommend the BLA route for Covaxin would make no difference to its use in India, said Vinod Paul, chair of the national expert panel on Covid-19 vaccination policy and member of the Niti Aayog.

“We respect that decision, and we expect our manufacturer will be able to comply by doing whatever is required. But it has no impact whatsoever on our own programme,” Paul said. “We are satisfied, our regulator has approved (the vaccine.) We have so much data on safety and its efficacy.”

India’s Covid-19 vaccination campaign has administered nearly 30 million doses of Covaxin. The country’s regulatory authority had approved the vaccine in January on the basis of earlier clinical trials assessing Covaxin’s safety and immune responses.

Sections of vaccine researchers say they do not understand what differential advantage Covaxin will provide in the US market that, they say, has sufficient stocks of the Covid-19 vaccines from Moderna, Pfizer and Johnson&Johnson.

A query sent by The Telegraph to Bharat Biotech asking what advantages might Covaxin provide over the vaccines already being used in the US market has not evoked a response.

Covaxin is made from inactivated (killed) virus, among the oldest of vaccination strategies, while the vaccines from Pfizer and Moderna are both designer mRNA vaccines, and the Johnson&Johnson vaccine is based on an adenovirus.

Santanu Tripathi, a former professor of pharmacology at the Calcutta School of Tropical Health, said variants might impact efficacy of the current vaccines in the future. “One expectation is that the whole virion vaccine might be more effective against variants,” he said.

But a senior virologist said mRNA vaccines were easier to tweak for variants. “I don’t see an advantage over mRNA vaccines,” the virologist told this newspaper. “This appears like a gamble on Bharat’s part.”

Bharat Biotech itself has underlined that no vaccine developed in India has ever received EUA or full approval from the US FDA. “Thus it will be a great leap forward for vaccine innovation from India when approved,” the company said in a media release.

The US FDA had on May 25 issued revised guidelines for EUA for Covid-19 vaccines that said it “may decline to review and process further EUA requests other than those for vaccines whose developers have engaged in an ongoing manner with the agency during the development of their manufacturing process and clinical trials programme”.