Covid-19: Covaxin booster has 77.8 per cent efficacy against variants

A citizen gets a booster dose of Covaxin at a BMC health post in Batliboy compound, Byculla. Pic/Ashish Raje

Amid the debate over the efficacy of a booster dose against new variants of SARS-CoV-2, the virus that causes COVID-19, a recent study published in the journal Nature Scientific Report stated that Covaxin is equally effective as 20 other global vaccines. Health experts, however, remained cautious and called for longer studies on preventing occurrence of autoimmune diseases in people with rheumatoid markers affecting heart, kidney, brain, blood and liver as a result of frequent booster doses.

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Vaccine efficacy

"Covaxin is an ancestral whole-virion inactivated SARS-CoV-2 vaccine that is adsorbed onto alum adjuvant to improve its immunogenicity. In 2020, the 6-µg dose of Covaxin was selected for assessment in a phase-3 efficacy trial in which it had demonstrated an overall efficacy of 77.8 per cent against any COVID-19 and 65.2 per cent against the Delta variant. A recently published Phase-2 double-blind study in a peer-reviewed medical journal that assessed the persistence of neutralising antibodies up to 6 months after a two or three doses of Covaxin in a randomised controlled trial. The study has reported persistence of humoral and cell mediated immunity up to 12 months. Administration of a third dose increased neutralisation titers against both ancestral and variant strains, namely Alpha, Beta, Delta, Delta Plus and Omicron, with persistent T-cell immunity. Thus, seroconversion rate remained high in boosted recipients compared to non boosted individuals, even after 6 months," said Dr Subhash Hira, professor of Global Health at University of Washington-Seattle and a member of several COVID-vaccine panels at WHO-Geneva.

He added, "However, some studies have raised concerns about excessive use of booster vaccines since they also cause production of auto-antibodies that lead to cardiomyopathies, brain clouding, and kidney-liver damages, in people who are predisposed to autoimmune diseases with rheumatoid markers."

"After analysing this report, it is clear that vaccines definitely help to protect against COVID-19 infection. So, we must encourage all people to take vaccines. Booster dose is also important to get protection against new variants of concern," said Dr Santosh Bansode, head of the department, Emergency Medicine, Wockhardt hospitals.

Dr Wiqar Shaikh, professor of Medicine, Grant Medical College and Sir JJ Group of Hospitals, said that he has noted the recent study on persistence of immunity and impact of third dose of Covaxin and added that the accepted norm worldwide is that boosters have to be given to protect the population. "However, there is no clarity on the no. of booster doses required. Besides, there has been a repeated demand everywhere that separate vaccines will need to be given for COVID-19 variants," he said.

MakerSpeak

In a media statement, M/s Bharat Biotech stated that the study was conducted on 184 subjects who were evaluated for safety, neutralising antibody responses against variants of concern, binding antibodies against spike protein, RBD, N proteins, and for memory T and B cell responses to demonstrate cell mediated immunity.

Dr Krishna Ella, chairman and MD, Bharat Biotech, said, "Our team has now demonstrated that Covaxin is a multi-epitope vaccine with antibodies against spike, RBD and N proteins. Post booster dose, it has proven neutralising antibody responses against variants of concern and long-term protection through memory T and B cell responses. We have now achieved our goal of developing a safe and efficacious vaccine with long term protection against a spectrum of variants."