Bharat Biotech’s coronavirus vaccine Covaxin showed 50% efficacy after two doses against symptomatic cases of Covid-19, a study published on Wednesday in medical journal The Lancet has found.
The number is significantly lower than the 77.8% efficacy that Bharat Biotech had found in the interim phase 3 trial results of Covaxin, released earlier in November.
The authors of the The Lancet study said the divergence in the results was due to several reasons. The Delta variant of the coronavirus was surging in India between April 15 and May 15, when the study was conducted, they said.
The study also noted that its participants were healthcare workers, who had more exposure to the coronavirus.
The study does not estimate vaccine efficacy against hospitalisation, severe disease and death, which require further assessment, the authors added.
The study was conducted among 2,714 hospital workers of the All India Institute of Medical Sciences in Delhi, who were symptomatic of the disease. All of them had received two doses of the Covaxin jab.
Of the 2,714 symptomatic health workers, 1,617 tested positive for the virus, the study showed.
“Our study offers a more complete picture of how BBV152 [Covaxin] performs in the field and should be considered in the context of Covid-19 surge conditions in India, combined with the possible immune evasive potential of the delta variant,” said Manish Soneja, additional professor of medicine at the All India Institute of Medical Sciences, according to The Lancet.
Covaxin has been used in India since India began its immunisation drive on January 16. The vaccine, however, was issued an emergency use listing (EUL) by the World Health Organization only on November 3.
The Drugs Controller General of India had granted approval for restricted emergency use to Covaxin in January. Covaxin and Oxford-AstraZeneca’s Covishield were the first Covid-19 vaccines to be approved in India.