Bharat Biotech's Covaxin was only 50 per cent effective against SARS-CoV-2 in real-world hospital settings during the months of March and April 2021, when the Delta variant was dominant, found doctors at the All India Institute of Medical Sciences. Published in the medical journal, The Lancet, the study finds that the vaccine's efficacy against the virus causing COVID-19 was lower than the 77.8 per cent claimed by the manufacturers in its clinical trials.
The authors of the study limited their sample size to people working at the hospital, were symptomatic, and had tested positive in the RT-PCR test. Furthermore, they ensured that participants who had received the BBV152 (scientific name of Covaxin) were considered to be a part of the study. AIIMS Delhi was exclusively vaccinating its 23,000 strong staff with Covaxin since January 16, 2021, the day the vaccines were launched. As the people working in hospitals are more prone to be exposed to the virus, the study adds that the occupation of the participants could be a potential reason for the decreased effectiveness.
The 50 per cent effectiveness was gauged after people developed symptoms 14 or more days after receiving both the doses of Covaxin. Initially enrolling 2714 patients, the study had 1068 participants that tested positive, and 1068 that tested negative for COVID-19.
Women were seen to respond better to Covaxin than men, the study suggests. The authors, however, rule out that the vaccine's performance is governed by biological changes.
The paper also highlights the delta variant's potential to evade the body's immune response. Even though the doctors did not identify the genetic make of the strain, the existing science, they state suggests that variants of concern such as the delta were circulating in those months and could have infected their participants. Delta is the same variant that originated in India and is widely responsible for the surge in cases across the world.
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This study only tested whether people suffered from COVID-19 after receiving the vaccine. The authors acknowledged that they did not check for hospitalisations and severity of the virus. They also further suggested that more studies should be undertaken in real-world settings to understand the implications of the vaccine on factors such as death, severity, and hospitalisations.
The Hyderabad manufacturer's clinical trial data also published in the Lancet finds that the vaccine is 65 per cent effective against the variant. These findings were shared with the World Health Organisation but published by the journal after Covaxin received emergency use approval by the apex health organisation.