Covaxin phase 3 data shows 78% efficacy against Covid

The homegrown Covid-19 vaccine Covaxin on Thursday received long-awaited scientific credence with one of the world's top medical journals publishing the final trial results showing its ability to offer 78 per cent protection against symptomatic Covid-19 and 93 per cent against severe disease.

The indigenous vaccine’s phase 3 clinical trial carried out in 25 hospitals between November 2020 and May 2021 involving 24,419 participants aged 18-97 years found that two doses of the vaccine have an efficacy of 77.8 per cent against symptomatic Covid-19 infection after two weeks, according to the interim analysis of the trial data published in the Lancet.

"We estimated vaccine efficacy of 77·8 per cent against symptomatic Covid-19 disease and, importantly, based on the limited data available, a higher efficacy against severe Covid-19 of 93·4 per cent. Thus, cases of severe disease, which require hospitalisation and have threatened to overwhelm health-care facilities, could be markedly decreased in fully vaccinated populations,” reported the Covaxin team that includes researchers from Indian Council of Medical Research (ICMR), National Institute of Virology, Pune and Bharat Biotech, Hyderabad, the manufacturer of the vaccine.

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The Lancet publication comes a week after Covaxin received the World Health Organisation’s (WHO) approval for emergency use listing, easing the life for lakhs of Indians whose international travel plans were hit due to the non-recognition of the shot.

More than 12 crore doses of Covaxin have been administered so far since the beginning of the vaccination campaign in January.

No severe vaccine-related adverse events were observed during the trial as most adverse events were mild and included headache, fatigue, and injection site pain.

While more than 24,000 individuals participated in the phase-3 trial, a smaller group of nearly 17,000 sero-negative people were considered for the efficacy analysis.

The analysis was conducted based on 130 laboratory-confirmed (RT-PCR positive) symptomatic Covid-19 among 16,973 initially sero-negative participants. All of these cases were recorded at least two weeks after participants had received a second dose.

The team recorded 24 positive cases among 8,471 people in the vaccine group and 106 positive cases among 8,502 people in the placebo group, suggesting an overall vaccine efficacy of 77.8 per cent. The efficiency improves to 79.4 per cent in people younger than 60 years but drops to 66 per cent among the senior citizens.

The researchers in their preliminary analysis, estimated vaccine efficacy of 65 per cent against the delta (B.1.617.2) variant but cautioned that further investigations were necessary and would be made to confirm Covaxin's clinical efficacy against Delta and other variants of concerns.

The vaccine has already received emergency use authorisation in several countries, including India, Iran, Mexico, and the Philippines, which are currently experiencing high SARS-CoV-2 prevalence and low to moderate vaccination coverage.

"The roll-out of BBV152 (Covaxin) might ease the ultra-cold chain requirements of other SARS-CoV-2 vaccine platforms, increase the finite global manufacturing capacity, and improve the insufficient supply of vaccines which disproportionately affects low-income and middle-income countries," wrote Jing-Xin Li and Feng-Cai Zhu of the Jiangsu Provincial Center for Disease Control and Prevention (China), who was not involved with the study, in a linked comment in the journal.

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