Two doses of Covaxin showed a 50 per cent effectiveness against symptomatic Covid-19 among healthcare workers during India’s second wave, the first real-world assessment of the effectiveness of Bharat Biotech’s vaccine has revealed.
The study published in the reported medical journal the Lancet infections Diseases assessed 2714 hospital workers who were symptomatic and underwent RT-PCR between April 15-May 15 this year when India was faced a devastating second wave. These health workers were offered Covaxin.
“The adjusted vaccine effectiveness against symptomatic Covid-19 after full vaccination with Covaxin, with the second dose administered 14 days or more before undergoing RT-PCR testing, was found to be 50 per cent,” the Lancet said. The effectiveness of two vaccine doses remained stable over the seven-week follow-up period.
The study found a trend towards better effectiveness in women than in men. This, it said might be attributable to differences in the roles that men and women have in the hospital rather than any biological differences.
Among the factors possibly responsible for the lower vaccine effectiveness than the efficacy announced could be the facts that the study was conducted only among hospital employees who have a higher risk of exposure to infection than the general population, and that the study was conducted during the peak of the second wave when test positivity rates were high in Delhi. Also, the prevalence of circulating variants of concern, especially delta, may have contributed to the lower effectiveness, the study said.
“The test-positivity rate for Delhi was around 35%, which was the highest it had been since the beginning of the pandemic. Thus, our results might only reflect the performance of BBV152 under such surge conditions,” it said.
The authors acknowledged several limitations in the study that the study did not estimate vaccine effectiveness against hospitalisation, severe disease, and death, which they said required further assessment.
“The exact duration of symptoms at the time of testing was not recorded. Thus, employees who presented late into the course of their illness might have had false-negative results, due to low clinical sensitivity of RT-PCR later in the course of the illness resulting in a biased estimate of vaccine effectiveness,” it said.
Covaxin was approved for emergency use in India for people aged 18 and above in January. Earlier this month, the World Health Organization (WHO) granted Emergency Use Listing (EUL) to Covaxin and added the vaccine to its list of approved emergency-use Covid vaccines.
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