The Omicron variant of the coronavirus has been detected in 89 countries as of December 16 and the number of cases is doubling in 1.5 to 3 days in areas with community transmission, the World Health Organization said.

In an update issued on Friday, the United Nations health agency said that Omicron was spreading fast even in countries with high level of herd immunity. Though it was unclear if the rapid increase in Covid-19 cases was due to “immune evasion, intrinsic increased transmissibility or a combination of both”.

The Omicron variant, which has a large number of mutations, was first detected in South Africa on November 24. Two days later, the World Health Organization declared it a “variant of concern”.

On Friday, the global health body said that the currently available data suggests that Omicron would take over the Delta variant in countries with community transmission of the infection.

The World Health Organization, however, said that there was limited data to ascertain the severity of Omicron.

“More data are needed to understand the severity profile and how severity is impacted by vaccination and pre-existing immunity,” it said. “Hospitalisations in the UK [United Kingdom] and South Africa continue to rise, and given rapidly increasing case counts, it is possible that many healthcare systems may become quickly overwhelmed.”

The update said that there was limited data available about the efficacy of vaccines on the new variant.

The World Health Organization also pointed out that the PCR and antigen-based tests continue to work on the variant.

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