Omicron infected have significant immune response, can neutralise Omicron, Delta: ICMR

Individuals infected with Omicron have significant immune response which could neutralise not only Omicron, but also other variants of concern, including the most prevalent Delta variant, an Indian Council of Medical Research (ICMR) study showed

The study analysed the IgG and neutralising antibodies (NAbs) against B.1, Alpha, Beta, Delta, and Omicron variants with the sera of individuals infected with the Omicron variant (B.1.1529 and BA.1). It suggests that the immune response induced by the Omicron could effectively neutralise the Delta variant, making re-infection with Delta variant less likely and displacing this varaint as the dominant strain.

This emphasises the need for an Omicron-specific vaccine strategy, said the study.

"The GMTs of neutralising antibodies of ChAdOx1 nCoV-19 breakthrough individuals showed significant fold-reductions compared to B.1 against Alpha (3.23), Beta (2.38), Delta (3.23) and Omicron (4.31) variants respectively. Similarly, BNT162b2 mRNA breakthrough individuals demonstrated significant fold-reduction in GMTs of 1.52 and 7.41 for Delta and Omicron respectively," it said.

However, the study has a limitation of lesser participants in the unvaccinated group and the shorter window period post infection. "This could be the important reason for the low immune response specifically in the unvaccinated individuals against Omicron," it said.

The study was conducted on 39 Omicron-infected individuals, of which 25 had taken both the doses of AstraZeneca Covid-19 vaccine, eight people had taken double dose of Pfizer jab, while six were unvaccinated. Of the 39, 28 were foreign returnees and the rest their high-risk contacts.

"Our study demonstrated substantial immune response in the individuals infected with Omicron. The neutralising antibodies could effectively neutralise the Omicron and other variants of concern (VOCs), including the most prevalent Delta variant," the study stated.