New Delhi: The interim data from a Phase 3 trial of Covaxin, India’s vaccine developed by Bharat Biotech and ICMR, has been peer-reviewed and published in The Lancet journal Friday. The study shows that two doses of the vaccine offer 77.8 per cent protection against symptomatic Covid.
Although Bharat Biotech in a statement in July had shared the efficacy data, the results of the trials were not published in any peer-reviewed journal.
The Lancet study indicates that the vaccine induces a robust antibody response. 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.
While the vaccine was approved for use in India in January this year, it wasn’t until last week that the vaccine received emergency use approval from the World Health Organization (WHO) for people aged 18 and older.
The trial took place between 16 November 2020 and 17 May 2021 across 25 hospitals in India with a total of 24,419 participants. Among them, 12,221 adults aged 18 and older were randomly assigned to receive two doses of the vaccine, while 12,198 were assigned to receive a placebo.
According to the vaccination policy in India, participants considered to be at risk of acquiring Covid were prioritised — with a total of 2,750 participants being above 60 years of age and 5,724 participants who reported at least one pre-existing medical condition, such as cardiovascular disease, diabetes, or obesity, across ages.
What the study focussed on was laboratory-confirmed (RT-PCR positive) symptomatic Covid, with onset at least 14 days after the second dose.
To check efficacy, the researchers picked 16,973 of the 24,419 participants who had initially tested negative for antibodies; 130 among them had tested positive for Covid.
A further break-up of the efficacy analysis shows that 24 of the positive cases came from 8,471 participants in the vaccine group and 106 came from 8,502 people in the placebo group, suggesting an overall vaccine efficacy of 77.8 per cent.
Among the 130 positive cases, 16 had severe Covid — one case out of 8,471 people in the vaccine group and 15 cases out of 8,502 people in placebo recipients.
The 16 patients included those who suffered from severe systemic illness, respiratory failure, evidence of shock, significant acute renal, hepatic, or neurologic dysfunction, admission to an intensive care unit, or death.
More research with larger sample size needed
However, the authors noted that this data is preliminary and more research with a larger sample size is needed to determine efficacy against severe disease and hospitalisation.
The team also looked at the concentration of neutralising antibodies in blood serum samples one month after receiving the second dose.
The vaccine-induced antibodies showed no significant decrease in neutralisation activity against the alpha (B.1.1.7) variant but demonstrated marginal reductions in neutralisation activity against other variants of concern, including the delta and gamma variants.
Preliminary analysis of efficacy against the Delta variant found Covaxin to be 65 per cent effective against symptomatic Covid infection. However, further observations are necessary to confirm clinical efficacy against Delta and other variants.
The study found no significant differences in immune responses across the broad age groups of under and over 60-year-olds. The oldest trial participant was 97 years of age.
This study has 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.
Some groups, including pregnant women, those living with HIV or with severe comorbidities, were specifically excluded from the study.
(Edited by Paramita Ghosh)