The Omicron variant of the coronavirus has been detected in 89 countries, and COVID-19 cases involving the variant are doubling every 1.5 to three days in places with community transmission and not just infections acquired abroad, the World Health Organization said overnight.
Omicron's "substantial growth advantage" over the Delta variant means it is likely to soon overtake Delta as the dominant form of the virus in countries where the new variant is spreading locally, the UN health agency said.
WHO noted that Omicron is spreading rapidly even in countries with high vaccination rates or where a significant proportion of the population has recovered from COVID-19.
It remains unclear if the rapid growth of Omicron cases is because the variant evades existing immunity, is inherently more transmissible than previous variants, or a combination of both, WHO said.
Other major questions about Omicron remain unanswered, including how effective each of the existing COVID-19 vaccines are against it.
Conclusive data also does not exist yet on how ill Omicron makes COVID-19 patients, the health agency said.
WHO first labeled Omicron a variant of concern on November 26.