Vaccine major Bharat Biotech on Wednesday said its Covid-19 vaccine, Covaxin, has demonstrated an interim vaccine efficacy of 81 per cent in the Phase 3 clinical trials.

The trials involved 25,800 subjects, the largest ever conducted in India, in partnership with the Indian Council of Medical Research, the Hyderabad-based company said in a statement.

Interim analysis also showed that severe, serious, and medically attended adverse events occurred at low levels and were balanced between vaccine and placebo groups, Bharat Biotech said.

The company also said that "analysis from the National Institute of Virology indicates that vaccine-induced antibodies can neutralise the UK variant strains and other heterologous strains".

This data, though, has yet to be peer-reviewed.

“Today is an important milestone in vaccine discovery, for science and our fight against coronavirus. With today’s results from our Phase 3 clinical trials, we have now reported data on our Covid-19 vaccine from Phase 1, 2, and 3 trials involving around 27,000 participants.

“Covaxin demonstrates high clinical efficacy trend against Covid-19 but also significant immunogenicity against the rapidly emerging variants,” said Dr Krishna Ella, Chairman and Managing Director, Bharat Biotech.

In a press release, Bharat Biotech explained the way in which Covaxin works.

“BBV152 contains a whole virion inactivated SARS-CoV-2 vaccine, which is produced in Vero cells. It is stable at 2 to 8°C (refrigerated) and is shipped in a ready-to-use liquid formulation that permits distribution using existing vaccine supply chain channels. BBV152 has a 28-day open vial policy as a unique product characteristic, thus reducing vaccine wastage by approximately 10-30%,” it said.

“BBV152 is based on an established manufacturing platform with a better safety profile when compared to other vaccine platforms. The inclusion of the Algel-IMDG adjuvant enhances T-cell immune responses to Covid-19, leading to long-term protection,” it further said.

Interim Phase 3 Results: 81% Efficacy

The Phase 3 study enrolled 25,800 participants between 18-98 years of age, including 2,433 over the age of 60 and 4,500 with comorbidities. The primary endpoint of Phase 3 clinical trial is based on the first occurrence of PCR-confirmed symptomatic (mild, moderate, or severe) Covid-19 with onset at least 14 days after the second study vaccination in serologically negative (to SARS-CoV-2) adult participants at baseline.

The first interim analysis is based on 43 cases, of which 36 cases of Covid-19 were observed in the placebo group versus 7 cases observed in the BBV152 (Covaxin) group, resulting in a point estimate of vaccine efficacy of 80.6%.

Bharat Biotech expects to share further details of the trial results as additional data become available. An additional interim analysis is planned for 87 cases, and the final analysis is planned for 130 cases. All data from the second interim and final analyses will be shared via pre-publication servers as well as submitted to a peer-reviewed journal for publication.

“I want to thank every one of the participants, who volunteered to participate in this vital clinical trial, our partners, principal investigators across 25 study sites, and our team at Bharat Biotech who dedicated their time to this vaccine discovery,” said Suchitra Ella, Joint Managing Director, Bharat Biotech.

Two vaccines being administered

Covaxin and Oxford-AstraZeneca's Covishield are the two vaccines that are being administered in the country.

The emergency approval of Covaxin raised eyebrows as it had not passed the Phase III trials when it received the green signal from the DCGI in January.

Congress leaders including Shashi Tharoor, Anand Sharma and Jairam Ramesh raised concerns about the “premature” approval of Covaxin for restricted emergency use.

BJP national president JP Nadda accused the Congress and other opposition parties of trying to cause panic among people to further their “failed politics and nefarious agendas”.

“Congress and the Opposition is not proud of anything Indian. They should introspect about how their lies on the Covid-19 vaccine will be used by vested interest groups for their own agendas,” he said in a series of tweets.