Lancet study on Covaxin: ‘Well tolerated, 77.8% efficient on COVID-19’

For Covaxin, the indigenously developed vaccine against symptomatic COVID, November has brought in good tidings.

Last week, after several months of wait, the World Health Organisation (WHO) authorised the vaccine for emergency use in those aged 18 or more. A week later, medical journal Lancet published the results of a phase 3 trial, which found that two doses of Covaxin offer 77.8% protection against symptomatic Covid.

“BBV152 (Covaxin) was highly efficacious against laboratory-confirmed symptomatic COVID-19 disease in adults. Vaccination was well tolerated with no safety concerns raised in this interim analysis,” said the report.

Bharat Biotech, which developed Covaxin in collaboration with the Indian Council of Medical Research (ICMR), did share the efficacy data in a statement issued in July. However, this is the first time that the interim trial results of the study — funded by Bharat Biotech and ICMR — are published in a peer-reviewed journal.

Trial methodology and results

The trial was conducted from 25 hospitals across India, between November 16, 2020, and May 17, 2021, on 24,419 participants. While 12,221 randomly selected adults were administered two doses of the vaccine, the balance 12,198 were given a placebo.

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The researchers further selected 16,973 of the 24,419 participants who had initially tested negative for antibodies (seronegative). Of these, 130 people tested positive for COVID; while 24 of them were from the 8,471 participants (out of 16,973) in the vaccine group, 106 came from the 8,502 participants of the placebo group. From this, the researchers concluded that the efficacy of Covaxin was 77.8%.

The study found Covaxin inducing a robust antibody response, and also bringing down the severity of the infection even when the participant tested positive. Of the 130 positive cases, 16 had severe COVID, of which 15 were from the placebo group.

There were no significant vaccine-related deaths or ‘adverse events’ post inoculation, said the report. “The most frequent solicited systemic adverse event overall was headache, followed by pyrexia (fever), fatigue, and myalgia, but in lower than 1% of participants in either group,” it added.

Study limitations

Raches Ella, Siddarth Reddy, William Blackwelder, and other authors of the study said the study had “several limitations”. “Due to the low number of cases reported between the first and second doses, we cannot calculate vaccine efficacy after a single dose. This report contains a median safety follow-up of 146 days from the first dose for all participants, and long-term safety follow-up of BBV152 is required and currently underway,” the wrote.

They further pointed out that the study population lacked ethnic and racial diversity, and that Covaxin needs to be tested for efficacy in other populations, too. They also stressed on the need for a larger sample size.