Scientists have detected two new virulent sub-variants of Omicron spreading covid-19 infection in India, weeks after sounding the alarm over two others in the run-up to festivities.

A total of 233 cases of sub-variants XBB and seven cases of XBB.1 have been found in various pockets to add to infections caused by the BF.7 and BF.5.1.7 strains detected earlier.

Indian SARS-CoV-2 Genomics Consortium (INSACOG) experts said XBB and XBB.1 are perhaps the most immune-evasive variants to date and evade the immune response of vaccines currently being used to treat covid.

However, none of these four sub-variants are known to have caused hospitalization or death in India.

Concerned over the surge in cases, scientists at INSACOG have kept a close vigil and are monitoring the emergence and evolution of such variants.

Public health experts said people should follow covid-appropriate behaviour to prevent a further spike. XBB was first detected in Singapore and the US and has spread to several countries and Indian states.

Last week, the World Health Organization (WHO) said Omicron remains a variant of concern, with early evidence pointing to XBB and XBB.1 posing a higher reinfection risk than other circulating Omicron sub-lineages.

Rajesh Gokhale, secretary of the department of biotechnology (DBT), said, “In the current phase of the pandemic, the SARS-CoV-2 virus is continuously accumulating mutations, some of which might contribute to increased transmissibility and immune evasion resulting in transmission advantage over other variants. XBB…is presently appearing in multiple countries. A sub-lineage of XBB with an additional mutation is also detected (XBB.1). In India, the Omicron sub-lineages or sub-variants keep diversifying. It has a few new spike mutations.”