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Explained: What phase 3 data says on Bharat Biotech’s Covaxin vaccine for Covid-19

Covaxin, the country’s first indigenous Covid-19 vaccine, was developed with seed strains received from the National Institute of Virology.

A nurse displays a Covaxin vial at a Covid-19 vaccination centre in Kolkata. (Express Photo: Partha Paul)

Covaxin, the vaccine manufactured by Bharat Biotech, has demonstrated overall interim clinical efficacy of 78 per cent, and 100 per cent efficacy against severe Covid-19 disease in phase 3 trials, the company and Indian Council of Medical Research (ICMR) announced on Wednesday.

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Vaccine and the study

Covaxin, the country’s first indigenous Covid-19 vaccine, was developed with seed strains received from the National Institute of Virology (NIV), using Whole Virion Inactivated Vero Cell derived platform technology. Inactivated vaccines do not replicate; they contain dead virus, which is incapable of infecting people but has the ability to trigger the immune system to mounting a defensive reaction against infection.

The vaccine received DCGI approval for phase 1 and 2 human clinical trials in July last year, and was introduced through Emergency Use Authorisation (EUA) under the clinical trial mode.

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The phase 3 clinical trial, which was co-funded by ICMR, enrolled 25,800 participants between the ages of 18 and 98 years, including 10 per cent over the age of 60, with analysis conducted 14 days post the second dose.

Interim analysis results

The phase 3 interim analysis results of Covaxin are based on more than 87 symptomatic cases of Covid-19. Due to the recent surge in cases, 127 symptomatic cases were recorded, resulting in a point estimate of vaccine efficacy of 78 per cent against mild, moderate, and severe Covid-19 disease, Bharat Biotech and ICMR said in a press release.

The efficacy against severe Covid-19 disease was 100 per cent with an impact on reduction in hospitalisations. Efficacy against asymptomatic Covid-19 infection was 70 per cent, suggesting decreased transmission in Covaxin recipients.


The safety and efficacy results from the final analysis will be available in June, and the final report will be submitted to a peer-reviewed publication, Bharat Biotech and ICMR said.

Based on the achievement of the success criteria, placebo recipients have now become eligible to receive two doses of Covaxin, Dr Krishna Ella, Bharat Biotech chairman and managing director, said. “The efficacy data against severe Covid-19 and asymptomatic infections is highly significant, as this helps reduce hospitalisations and disease transmission respectively,” he said.

Works against variants

Scientists at ICMR-NIV said they have isolated and cultured all variants of concern — B.1.1.7 (UK variant), B. (Brazil variant), B.1351 (South Africa variant) and the double mutant strain B.1.617 (E484Q and L452R) found in certain parts of the country — and demonstrated the neutralisation potential of Covaxin against the UK and Brazil variants.


While data for the South Africa variant is being generated, Covaxin has been found to effectively neutralise the double mutant strain, NIV scientists have said. “The tireless efforts of our scientists at ICMR and BBIL (Bharat Biotech) have resulted in a truly effective international vaccine… Covaxin works well against most variants of SARS-CoV-2,” ICMR Director General Prof Balram Bhargava said.

Minimal post-jab infection

Around 1.1 crore of the total doses administered in India so far have been Covaxin; 93.56 lakh of these have been first doses. Barely 0.04 per cent (4,208) recipients returned a positive result for Covid-19 after receiving the first dose of Covaxin, Dr Bhargava said.

Of the 17.37 lakh beneficiaries who have received the second dose of Covaxin, 695 caught the “post-vaccination breakthrough infection”, almost the same percentage as those after the first dose.

For Covishield, which has been by far the dominant vaccine, these numbers were 0.02 per cent (17,145 out of 10.03 crore) for the first dose, and 0.03 per cent for the second dose (5,014 positive out of 1.57 crore), according to government figures.

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Ramping up capacity

Suchitra Ella, Bharat Biotech joint managing director, said efforts were underway to further develop Covaxin, with clinical trials planned in India and globally to evaluate its safety and immunogenicity in younger age groups, the impact of booster doses, and protection against SARS-CoV-2 variants.


More than 60 countries globally have expressed interest in Covaxin, and Emergency Use Authorisations have been received from several countries, the company said.

“Our development efforts have been transparent and published in six peer-reviewed journals, with additional publications in process,” it said in the press release.


“The capacity expansion has been implemented across multiple facilities in Hyderabad and Bangalore to reach ~ 700 million doses/year, one of the largest production capacities for inactivated viral vaccines worldwide.”

First published on: 22-04-2021 at 04:00:50 am
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