BENGALURU, Nov 24 ― Bharat Biotech's vaccine was only 50% effective at preventing symptomatic Covid-19 in a high-risk population during a devastating second wave of infections in India this year, data gleaned from hospital workers showed.

The real world study for Covaxin, conducted April 15-May 15, compares with a 77.8 per cent effectiveness rate in a late-stage trial of more than 25,000 participants that was conducted November 2020 to January 2021.

The new data analysed just over 1,000 Covid-19 cases with a test-negative control case group, matching by age and gender, according to the study which was published in the Lancet Infectious Diseases journal.

The much lower effectiveness rate for the two-dose shot seen in the new study can possibly be attributed to the fact that the study was restricted to hospital employees who had a higher risk of being infected than the general population, that it was conducted during a surge in infections and also to the prevalence of the Delta variant at the time, the study concluded.

Covaxin, which Bharat Biotech co-developed with an Indian research body, received emergency-use authorisation in India in January even before the completion of the late-stage trial.

It is the only homegrown vaccine being used in India's vaccination programme, although it accounts for only about 11 per cent of the 1.18 billion doses administered so far.

Covaxin has also been approved in countries such as Vietnam and Brazil. Bharat Biotech's US partner, Ocugen, has submitted a request to the US FDA for emergency use approval. ― Reuters