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Covaxin Shows 50% Effectiveness Against Symptomatic Covid-19 In Real-World Assessment: Lancet Study

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The results of an interim study recently published in The Lancet showed that two doses of Covaxin, also known as BBV152, had 77.8 per cent efficacy against symptomatic disease and present no serious safety concerns.

The latest study assessed 2,714 hospital workers at the All India Institute of Medical Sciences (AIIMS) in Delhi, from April 15, who were symptomatic and underwent RT-PCR test for COVID-19 detection.

Researchers noted that the Delta variant was the dominant strain in India during the study period, accounting for approximately 80 per cent of all confirmed COVID-19 cases. Covaxin, developed by Hyderabad-based Bharat Biotech in collaboration with the National Institute of Virology, Indian Council of Medical Research (NIV-ICMR), Pune, is an inactivated whole virus vaccine administered in a two-dose regimen, 28 days apart.

In January this year, Covaxin was approved for emergency use in India for people aged 18 and above. The World Health Organization (WHO) added the vaccine to its list of approved emergency use COVID-19 vaccines earlier this month. The latest study was conducted during India's second COVID-19 surge and in healthcare workers who were primarily offered Covaxin.

The COVID-19 vaccination centre at AIIMS New Delhi exclusively offered Covaxin beginning January 16 this year to all of its 23,000 employees. Researchers evaluated the effectiveness of the vaccine against symptomatic RT-PCR confirmed SARS-CoV-2 infection. Of the 2,714 employees in the study population, 1,617 people tested positive for SARS-CoV-2, the virus that causes COVID-19, and 1,097 tested negative.

Positive cases were matched to negative RT-PCR tests (controls). The odds of vaccination with Covaxin were compared between cases and controls and adjusted for occupational exposure to COVID-19, previous SARS-CoV-2 infection, and infection dates.

The study found that the vaccine effectiveness against symptomatic COVID-19 after two doses of Covaxin with the second dose administered 14 or more days before undergoing RT-PCR testing was 50 per cent. The effectiveness of two vaccine doses remained stable over the seven-week follow-up period, the researchers said.

The adjusted vaccine effectiveness of the first dose, estimated after seven and 21 days, was low, which is consistent with the performance of other preventives against the Delta variant, they said.

The authors acknowledge that the vaccine effectiveness of Covaxin estimated in this study is lower than the efficacy reported by the recently published phase 3 trial. They noted that several factors may be responsible for the lower vaccine effectiveness in the latest study.

The researchers said this study population only included hospital employees who may have a higher risk of exposure to COVID-19 infection than the general population. The research was conducted during the peak of India's second wave of COVID-19 with high test positivity rates for both hospital employees and residents of Delhi, they said.

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