Covaxin booster dose shields against Delta, Omicron variants: ICMR-NIV study

A NEW study by the Indian Council of Medical Research (ICMR)-National Institute of Virology (NIV) and Bharat Biotech shows that a Covaxin booster dose is effective against both the Delta as well as Omicron variants BA.1.1 and BA.2 of Covid-19.

“The booster dose of Covaxin was found to improve the neutralising antibody response against VoCs (variants of concern), including Delta and the Omicron. This is a promising study,” Dr Samiran Panda, Additional Director-General, ICMR, told The Indian Express.

The findings are based on a study that has been conducted on animals and will be followed up in human trials as well. The study was conducted earlier but it takes time to get published as per the protocol, said Dr Panda.

The ICMR-NIV study has been published as a pre-print in bioRxiv and posted on June 14 as “Protective efficacy of Covaxin against Delta and Omicron variants in the hamster model”.

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Researchers from 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 (animal model to study human-associated diseases).

The antibody response, clinical observations, viral load reduction and lung disease severity after the virus challenge were studied. Protective response in terms of the reduction in lung viral load and lung lesions were observed in both the second and third doses of the Covaxin immunised group compared to a placebo group following the Delta variant challenge, the authors of the study said in the report.

In the Delta infection study, researchers compared the protective response between the second and third dose regimens and said that 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 reduced after the third dose vaccination.

In the second study, in which protective response was assessed against Omicron variants BA.1 and BA.2 after three dose vaccinations, the test cases reported lesser virus shedding, lung viral load and lung disease severity.

Immunity generated by the natural infection or vaccination tends to wane with time, and according to the study authors, newly evolving variants have also posed challenges to the acquired immunity with their immune escape properties. This necessitates the importance of constant monitoring of the virus genomic changes and the properties of the evolving variants, researchers say. Booster doses have shown to improve the efficacies of many Covid-19 vaccines in clinical trials and have been authorised by regulatory authorities in many countries.

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