The World Health Organization (WHO) said on Saturday said that the number of Omicron cases is doubling in 1.5 to 3 days in areas with community transmission.

89 countries have reported the Omicron coronavirus variant.

With high levels of population immunity, Omicron is spreading rapidly in countries.

The WHO said in an update that it is unclear if this is due to the virus's ability to evade immunity, its inherent increased transmissibility, or a combination of both.

The agency designated Omicron a variant of concern on Nov 26, soon after it was first detected. However much about the variant is still not known, including the severity of the illness it causes.

The WHO said, "There are still limited data on the clinical severity of Omicron."

"More data are needed to understand the severity profile and how severity is impacted by vaccination and pre-existing immunity.

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