Interim data from a phase 3 trial of the Covid-19 vaccine Covaxin, developed in India by Bharat Biotech, show that two doses offer 77.8% protection against symptomatic Covid. The findings have been published in The Lancet. It comes days after Covaxin received emergency use approval from the World Health Organization (WHO) for people aged 18 and older.
Covaxin, or BBV152, is an inactivated whole virion vaccine formulated with a novel adjuvant and administered in a two-dose regimen, 28 days apart.
The study was funded by Bharat Biotech International Limited and the Indian Council of Medical Research (ICMR). The trial took place between November 16, 2020 and May 17, 2021. It included 25,798 adult participants, of whom 24,419 adults were randomly assigned to receive two doses of the vaccine (12,221) or a placebo (12,198). The participants received the doses in 25 hospitals across the country.
The efficacy analysis was based on 130 symptomatic Covid-19 cases among 16,973 participants who were initially seronegative. These cases were recorded at least two weeks after participants had received a second dose.
There were 24 positive cases in the vaccine group (8,471 people) and 106 in the placebo group of 8,502, suggesting an overall efficacy of 77.8%.
Among the positive cases, there were a total of 16 cases of severe symptomatic Covid-19 disease. These included one in the vaccine group and 15 in the placebo group.
The findings indicate that Covaxin induces a robust antibody response, the paper said. No severe vaccine-related adverse events or deaths were reported among the trial participants. The majority of the adverse events, including headache, fatigue, fever, and pain at the injection site, were mild and occurred within seven days of vaccination.
Covaxin is one of three vaccines being administered in India, alongside Covishield and Sputnik V (which constitutes a very small fraction of the total doses given). Covishield, from the Serum Institute is a version of the Oxford-AstraZeneca vaccine, or ChAdOx1 nCoV-19.
In the Covaxin study, researchers conducted a preliminary analysis of efficacy against the Delta variant and found the vaccine to be 65% effective against symptomatic Covid-19 infection from this delta variant. They noted, however, that this data should be presented as preliminary and further observations are necessary to confirm clinical efficacy against Delta and other variants.
The authors of the Covaxin study have noted that the data are preliminary, and more research with a larger sample size is needed.
They cited several limitations. Due to the low number of cases reported between the first and second vaccine doses, the researchers could not calculate vaccine efficacy after a single dose.
The data on efficacy against variants other than Alpha and Delta must be considered preliminary; the numbers reported are small, they said.
The study population was limited to India and therefore lacked ethnic and racial diversity, underscoring the importance of evaluating the efficacy of the vaccine in other populations.
Some groups, including pregnant women, and those living with HIV or with severe comorbidities, were excluded by the study inclusion/exclusion criteria.
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