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"... Covaxin demonstrated 81 per cent interim efficacy in preventing COVID-19 in those without prior infection after the second dose," Bharat Biotech said in its statement.
Covaxin's Phase III trials, which began in November last year, involved 25,800 participants aged between 18 and 98 across 25 sites. Participants, who included 2,433 over 60 and 4,533 with co-morbidities, were randomly divided into two groups. One got the vaccine and the other a placebo. Bharat Biotech said an "initial interim analysis" of 43 participants who contracted the infection showed 36 had been given a placebo.
Dr Randeep Guleira, the chief of Delhi's AIIMS, told NDTV the interim data was "very encouraging", would serve as a big boost to vaccine efforts and, crucially, help overcome vaccine hesitancy as India pursues its inoculation drive. He also said a sufficient number - around 130 infections - was needed for a statistically significant analysis.
"To see efficacy, you need to have a sufficient number who get infected... and you don't know which group got the vaccine and which the placebo. When you have a sufficient number of positive cases, you can say efficacy is based on good data," he said.
"After 43 events they broke the code (checked to see who got the vaccine and who the placebo) and, based on that, vaccine shows efficacy of around 81 per cent. But we need around 130-140 cases and then break the code to get real efficacy ," he explained.
Bharat Biotech has said it expects to share further details. "An additional interim analysis is planned for 87 cases, and the final analysis is planned for 130 cases. 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," the company said.
Interim analysis also showed severe, serious, and medically attended adverse events occurred at low levels and were balanced between the two groups. The company also said that "analysis from the National Institute of Virology indicates that vaccine-induced antibodies can neutralise the UK variant strains and other heterologous strains".
Data from the third stage of trials - which measures the vaccine's success in protecting against the virus - was widely anticipated amid concerns over Covaxin's efficacy, particularly as mutated, and more infectious, strains are circulating. As of March 1, there are 213 cases of the UK, Brazilian and South African strains in the country. It also comes as several states, including Maharashtra, see a worrying spike in new cases.
Covaxin is one of two Covid vaccines to have been cleared for emergency use. The other is Covishield, which was developed by AstraZeneca and Oxford University and is produced by Pune-based Serum Institute. Covishield has 70 per cent efficacy after the second dose. Both are being used in the first and second phase of the vaccination drive.
Both vaccines were cleared by the Drug Controller General of India (DCGI) in early January, at a time when late-stage trial data for Covaxin was not available; it was cleared on the basis of Phase I and II data that confirmed its "safety and immunogenicity". Covaxin was given "restricted use in emergency situation in public interest".