Two doses of Covaxin, India's indigenous COVID-19 vaccine, offer 77.8 per cent protection against symptomatic disease and present no serious safety concerns, according to an interim analysis of its phase 3 trial published in The Lancet on Friday.
Covaxin, an inactivated whole virus vaccine developed by Hyderabad-based Bharat Biotech, recently received emergency use approval from the World Health Organisation (WHO) for people aged 18 and above.
The phase 3 trial findings indicate that Covaxin induces a robust antibody response with no severe vaccine-related adverse events or deaths reported among the trial participants, the authors of the study said.
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, they explained.
The vaccine is administered in a two-dose regimen, 28 days apart, and can be stored and transported between 2-8 degrees Celsius.
The trial took place from November 16 to May 17 this year, with participants aged 18 and older randomly assigned to receive two doses of the vaccine or a placebo.
The researchers '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 authors said.
They also noted that the data is preliminary and more research with larger sample size is needed to determine efficacy against severe disease and hospitalisation.
Participants considered to be at risk of acquiring COVID-19 were prioritised with 2,750 participants 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.
This study was conducted with participants from diverse geographic locations across 25 hospitals in India.
The researchers conducted an efficacy analysis based on 130 laboratory-confirmed RT-PCR positive symptomatic COVID-19 among 16,973 initially seronegative participants.
These cases were recorded at least two weeks after participants had received a second dose.
The trial also found that Covaxin was well-tolerated among all trial participants, with 12 per cent of vaccine and placebo groups reporting an adverse event.
'The peer-review of Covaxin phase III clinical trial data in The Lancet, an authoritative voice in global medicine validates our commitment to data transparency and meeting the stringent peer-review standards of world-leading medical journals,' said Bharat Biotech Chairman Krishna Ella.
'The data from our product development and clinical trials have been published in 10 peer-reviewed journals, making Covaxin one of the most highly published COVID-19 vaccines in the world,' Ella said in a statement.
The study authors from Bharat Biotech and National Institute of Virology, Indian Council of Medical Research (NIV-ICMR), Pune, noted that there was no clinically or statistically significant difference in serious adverse events between groups, and no cases of vaccine-related deaths.
'I am delighted to see that the phase III efficacy data has also been published in The Lancet, one of the most reputed journals worldwide. This itself speaks high about the strong position of Covaxin amongst other global front-runners COVID-19 vaccines,' said Indian Council of Medical Research Director General Balram Bhargava.
Analysis of immune responses induced by the vaccine showed that Covaxin produced a strong neutralising antibody response measured by the concentration of these antibodies at day 56 or one month after receiving the second dose.
A neutralising antibody defends a cell from an infectious particle by preventing any effect it has biologically.
Similar to the phase 1/2 studies, Covaxin-induced antibodies showed no significant decrease in neutralisation activity against the Alpha variant but demonstrated marginal reductions against other variants of concern, including Delta and Gamma.
Researchers conducted a preliminary analysis of efficacy against the Delta variant and found Covaxin to be 65 per cent effective against symptomatic COVID-19 infection from the variant.
They, however, cautioned that this data is preliminary and 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 old.
The authors of the study also noted several limitations of the analysis.
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.
They said the analysis included safety follow-up of an average 146 days from the first dose for all participants, adding that long-term safety follow-up of Covaxin is required and is currently underway.
The study population was limited to India and therefore lacked ethnic and racial diversity, underscoring the importance of evaluating the efficacy of Covaxin in other populations.
'The roll-out of Covaxin might ease the ultra-cold chain requirements of other SARS-CoV-2 vaccine platforms, increase the finite global manufacturing capacity, and improve insufficient supply of vaccines which disproportionately affects low-income and middle-income countries,' said Jing-Xin Li and Feng-Cai Zhu of the Jiangsu Provincial Center for Disease Control and Prevention, China, who were not involved in the study.
'The next step for studies of Covaxin should be a focus on monitoring for epidemiological variations in SARS-CoV-2 and the long-term vaccine efficacy against symptomatic COVID-19 and asymptomatic infection to identify whether the vaccine provides ongoing protection when any variant of concern has occurred,' Zhu said in a statement.