Hyderabad-based Bharat Biotech on Wednesday said that its Covid-19 vaccine Covaxin showed an overall efficacy 78%, according to an interim analysis of its third phase of clinical trials. This was slightly lower than the 81% efficacy reported by the company in March.

The efficacy against severe Covid-19 disease, however, was 100%, the company said. The analysis was on a data set of 127 coronavirus positive volunteers.

Covaxin is one of the two vaccines being used in India’s vaccination drive and is the country’s first successful home-made shot against Covid-19. It is developed in collaboration with the Indian Council of Medical Research, the National Institute of Virology and vaccine manufacturer Bharat Biotech.

The Phase 3 study enrolled 25,800 participants between 18-98 years of age, including 2,433 over the age of 60 and 4,500 with comorbidities, with the analysis conducted 14 days post the second dose.

“Efficacy against SARS-Cov-2 has been established,” the company said. “Covaxin has demonstrated an excellent safety record in human clinical trials and in usage under emergency use”

Bharat Biotech’s Chairperson and Managing Director Krishna Ella said that its efficacy data against severe Covid-19 and asymptomatic infections was highly significant “as this helps reduce hospitalisations and disease transmission, respectively”.

The company said safety and efficacy results from the final analysis would be available in June and the final report will be submitted to a peer-reviewed publication. “Based on the achievement of the success criteria, placebo recipients have now become eligible to receive two doses of COVAXIN,” Bharat Biotech said.

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Covaxin was granted emergency use authorisation along with Serum Institute of India’s Covishield ahead of India’s countrywide vaccination programme that started on January 16.

However, the vaccine’s use in the inoculation drive raised concerns among experts as the Central Drugs and Standards Committee approved it for use before completing the third phase human trials. Health authorities, including ICMR chief Balram Bhargava and Union Health Minister Harsh Vardhan, however, have said the shot is “safe and immunogenic”.

In January, preliminary data of its Phase 1 trials published in The Lancet journal showed that the vaccine was well tolerated and induced enhanced immune response with neutralising antibodies among participants.

Earlier on Wednesday, the Indian Council of Medical Research said that Covaxin effectively neutralises the double mutant strain of SARS-CoV-2 and other variants.