Covaxin booster safe, necessary as it ensures persistent immunity: ICMR study
NEW DELHI: The Covaxin booster dose is safe and necessary as it ensures persistent immunity that minimises breakthrough Covid infections, said a new Indian Council of Medical Research (ICMR) study.
Published in the Nature - Scientific Reports Journal, the study said no serious adverse events were observed, except pain at the injection site, itching and redness.
With the government pushing for precaution doses in the country, as only eight per cent of the population in the over 18 years of age group has taken booster doses, the study said it is well known that neutralising antibodies induced by Covid-19 vaccines wane within six months of vaccination leading to questions on the effectiveness of the two-dose vaccination against breakthrough infections.
The study said that the administration of the third dose of BBV152 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 said that a booster dose of Covaxin, India's indigenous Covid-19 vaccine developed by Hyderabad-based Bharat Biotech in collaboration with the Indian Council of Medical Research (ICMR) – National Institute of Virology (NIV), showed an 18.5-fold increase in neutralisation antibody titers against the Omicron variant, as compared with the non-booster does recipient.
"Thus, seroconversion rate remains high in boosted recipients compared to non-booster, even after six months, third post dose against variants," said Dr Pragya Yadav, one of the authors of the study, 'persistence of immunity and impact of the third dose of inactivated Covid‐19 vaccine against emerging variants'.
Seroconversion rates are one of the methods used for determining the efficacy of a vaccine. "Hence, these results indicate that a booster dose of BBV152 is safe and necessary to ensure persistent immunity to minimise breakthrough infections of COVID-19 due to newly emerging variants," the study added.
The report said that, 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.
Yadav, a top scientist at ICMR-NIV who was also awarded for her work on vaccine development, said that the emergence of SARS-CoV-2 variants of concern had raised questions about the durability of the neutralising antibody responses.
"Diminished vaccine effectiveness against variants of concern such as Alpha, Beta, Delta and Omicron has been reported for several authorised vaccines with two doses of vaccination," she said.
Understanding the persistence of neutralising antibody responses against variants of concern has become vital to assess the need for additional booster doses, said the lead author, Krishna Mohan Vadrevu, director with Bharat Biotech International Limited (BBIL).
The researchers assessed the persistence of immunogenicity up to six 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.
For the booster dose trial, around 184 from the parent study were re-enrolled to receive the preventive dose or placebo.
A decline in antibody levels after the second dose of Covaxin was found.
However, more than 75 per cent of participants who followed up six months after the amount still had detectable neutralising antibody responses to the homologous SARS-CoV2 strain D614G, the study said