"As case numbers linked to a variant of concern increase globally, we expect the number of hospitalised cases and even deaths to be reported", the WHO said in a statement.
On Monday, the United Kingdom Health Security Agency confirmed the first Omicron-related fatality.
Many countries still do not have the capacity to consistently analyze all cases or deaths, so it can be difficult to provide accurate information on deaths related to a particular variant, the WHO said, adding that more information on the severity of the Omicron strain is expected in the coming weeks due to time lag between an increase in the number of cases and an increase in the number of severe cases and deaths.
"Further information is needed to fully understand the clinical picture of those infected with Omicron and WHO encourages countries to contribute to the collection and sharing of hospitalised patient data through the WHO COVID-19 Clinical Data Platform", the statement read.
The organisation dubbed the Omicron strain, which emerged in South Africa, a variant of concern earlier this month, citing its high number of mutations (32).