A new study conducted by the Indian Council of Medical Research (ICMR), the National Institute of Virology (NIV) and Bharat Biotech has shown that a Covaxin booster dose is effective against both the Delta variant and the Omicron sub-variants BA.1.1 and BA.2.
“The booster dose of Covaxin was found to improve the neutralising antibody response against variants of concern, including Delta and Omicron. This is a promising study,” said Dr Samiran Panda, additional director-general of the ICMR.
The findings are based on a study conducted on animals and it will be followed up in humans as well. The study was conducted earlier but it took time to get published as per the protocol, Dr Panda said.
The ICMR-NIV study was published as a pre-print in bioRxiv on Tuesday under the title “Protective efficacy of Covaxin against Delta and Omicron variants in the hamster model.”
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Researchers from the NIV and Bharat Biotech analysed the protective efficacy of Covaxin following second- and third-dose immunisations against the Delta variant, and studied the efficacy of the same vaccine against Omicron variants in a Syrian hamster model.
The antibody response, clinical observations, viral load reduction and lung disease severity after the virus challenge were studied. Protective responses in terms of the reduction in the lung viral load and lung lesions were observed in both the second and third doses in a Covaxin-immunised group compared to a placebo group following the Delta variant challenge, the study’s authors have said in the report.
In the Delta infection study, researchers compared the protective responses between the second- and third-dose regimens and said they could observe the advantage of the booster dose vaccination. Although the neutralising antibody levels were comparable among the groups, lung disease severity was found more reduced after the third dose.
In the second study, in which the protective response was assessed against Omicron sub-variants BA.1 and BA.2 after three doses of vaccination, the test cases reported less virus shedding, a low lung viral load and lung disease severity.
The immunity generated by the natural infection or vaccination tends to wane with time, and according to the study authors, newly evolving variants also pose challenges to acquired immunity with their immune-escape properties. This underlines the importance of constant monitoring of the virus’s genomic changes and the properties of the evolving variants, the researchers have said.
Booster doses have shown to improve the efficacy of many Covid-19 vaccines in clinical trials and have been authorised by many countries.
Covaxin is an inactivated, whole-virion vaccine licensed in India and 13 other countries. It has shown immunogenicity and protective efficacy against the coronavirus’s B.1 variant possessing the D614G mutation in laboratory animal studies. With the emergence of coronavirus variants, multiple in-vitro studies were conducted to understand the neutralisation potential of the Covaxin-induced immune responses.
The neutralisation potential has been demonstrated with the Alpha, Kappa, Beta, Delta and Omicron variants of the virus. But the neutralising antibody titres against the variants of concern were found reduced in comparison to the ancestral B.1 variant. Among these variants, Omicron was least effectively neutralised in the in-vitro assay. According to the study findings, researchers have said that Covaxin will enhance vaccine effectiveness against Delta-variant infection and protect against Omicron variants BA.1.1 and BA.2.