With the Centre rolling out free booster doses from Friday, a new Indian Council of Medical Research (ICMR) study has indicated that the precautionary dose of Covaxin ( BBV152) is safe to ensure persistent immunity to minimise breakthrough infections of Covid-19, due to newly emerging variants. The study also showed an 18.5-fold increase in neutralisation antibody titers against the Omicron variant after a Covaxin booster dose, as compared with the non-booster dose recipient.
The administration of a third dose of Covaxin increased neutralisation titers against both homologous (D614G) and heterologous strains (Alpha, Beta, Delta, Delta Plus and Omicron) with a slight increase in B cell memory responses, the study ‘Persistence of Immunity and Impact of Third Dose of Inactivated Covid‐19 vaccine Against Emerging Variants’ published on July 14 in Nature -Scientific Reports journal has said.
In addition, sera collected after six months post a third dose was also evaluated for neutralisation efficiency. Results showed that Covaxin generated higher neutralisation efficiency against D614G, Delta and Omicron variants and the antibody titers are persistent even after 12 months of primary vaccination.
Study researchers have said in the report that the emergence of SARS-CoV-2 variants of concern has raised questions about the durability of the neutralising antibody responses. Diminished vaccine effectiveness against variants of concern such as Alpha, Beta, Delta and Omicron have been reported for several authorised vaccines with two doses of vaccination, they pointed out.
Understanding the persistence of neutralising antibody responses against variants of concern has become vital to assess the need for additional booster doses, Krishna Mohan Vadrevu, director with Bharat Biotech International Limited (BBIL), has said in the report. BBIL, along with scientists from Indian Council of Medical Research-National Institute of Virology, Pune, Nizam’s Institute of Medical Sciences, Hyderabad, All India Institute of Medical Sciences, Patna, and others assessed the persistence of immunogenicity up to 6 months after two or three doses of Covaxin and the safety of a booster dose in an ongoing phase 2, double-blind, randomised controlled trial .
There was a decline of antibody levels after the second dose of Covaxin. However, more than 75 per cent participants followed up six months after the dose still had detectable neutralising antibody responses to the homologous SARS-CoV2 strain D614G, Dr Pragya Yadav, senior scientist from ICMR-NIV, noted in the report.
For the booster dose trial, around 184 from the parent study were re-enrolled to receive the precautionary dose or placebo. The seroconversion rate remains high in boosted recipients compared to non-booster, even after six months, post third dose against variants. No serious adverse events were observed, except pain at the injection site, itching and redness, study researchers have said.