Bharat Biotech's vaccine, whose emergency use approval before finishing final stage testing had triggered a row, has shown an 81 per cent efficacy in preventing symptomatic COVID-19 in an interim analysis of the advanced clinical trial, the company said on Wednesday, boosting prospects of its usage.
Covaxin, which was shunned by some health workers due to lack of final trial data, showed efficacy better than the company's previous guidance of around 60 per cent.
In a statement, Bharat Biotech Chairman Krishna Ella said Covaxin has 'demonstrated high clinical efficacy' as also shown 'significant immunogenicity' against rapidly emerging variants.
In a separate video address, he added that 'many people criticised us'.
The results come as a shot in the arm for India's immunisation drive against coronavirus.
The drug regulator in January had allowed Covaxin as well as the vaccine made by AstraZeneca's local partner, the Serum Institute of India Ltd.
But the lack of final trial data inhibited the use of Covaxin, which made up for only about 11 per cent of the more than 1 crore vaccines administered till last week.
The findings cement Bharat Biotech's claims of India's first successful home-made COVID-19 vaccine being safe while also brightening prospects for sales overseas.
The Hyderabad-based firm said it already has attracted interest from more than 40 countries.
The second phase of vaccination opened this week with Prime Minister Narendra Modi taking a shot of Covaxin.
Bharat Biotech said the efficacy data was based on tests on 25,800 subjects, the largest ever conducted in India.
The Phase 3 study enrolled participants between 18-98 years of age, including 2,433 over the age of 60 and 4,500 with comorbidities, it added.
The first interim analysis is based on 43 cases, of which 36 cases of COVID-19 were observed in the placebo group versus 7 cases observed in the COVAXIN group, resulting in a point estimate of vaccine efficacy of 80.6 per cent, Bharat Biotech said.
"Today is an important milestone in vaccine discovery, for science and our fight against coronavirus. With today's results from our Phase 3 clinical trials, we have now reported data on our COVID-19 vaccine from Phase 1, 2, and 3 trials involving around 27,000 participants," Ella said.
Covishield, manufactured by the Serum Institute, had shown an efficacy rate of 70 per cent after two full doses.
However, one of the regimens with a half dose and a full dose showed 90 per cent efficacy against the virus.
Bharat Biotech said the interim analysis of its vaccine included a preliminary review of the safety database, which showed that severe, serious, and medically attended adverse events occurred at low levels and were balanced between vaccine and placebo groups, the company said.
The trial's conduct and monitoring are as per good clinical practice guidelines and have been outsourced to IQVIA, it added.
"Analysis from the National Institute of Virology indicates that vaccine-induced antibodies can neutralize the UK variant strains and other heterologous strains," Bharat Biotech said.
The company expects to share further details of the trial results as additional data becomes available, it noted.
An additional interim analysis is planned for 87 cases, and the final analysis is planned for 130 cases, the company said.
All data from the second interim and final analyses will be shared via pre-publication servers as well as submitted to a peer-reviewed journal for publication, it added.