The omicron coronavirus variant has been reported in 89 countries and the number of cases is doubling in 1.5 to 3 days in areas with community transmission, the World Health Organization (WHO) said on Saturday.

Omicron is spreading rapidly in countries with high levels of population immunity, but it is unclear if this is due to the virus’ ability to evade immunity, its inherent increased transmissibility or a combination of both, the WHO said in an update.

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

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