First detected in southern Africa last month and dubbed a "variant of concern" by the WHO, scientists are still gathering data to establish how contagious Omicron is, and the severity of the illness it causes.
It has been reported in at least two dozen countries, and started gaining a foothold in Asia this week, with cases reported from Australia, Japan, South Korea, Singapore, Malaysia and India. Many governments have responded by tightening travel rules.
"Border controls can buy time but every country and every community must prepare for new surges in cases," Takeshi Kasai, WHO regional director for the western Pacific, told a virtual media briefing.
Kasai added that countries must utilize lessons learned from dealing with the Delta variant and urged them to fully vaccinate vulnerable groups and implement preventive measures such as mask wearing and social distancing rules.