Schiphol Airport in the Netherlands, where 61 people who flew back from South Africa are positive for COVID-19. (Illustration photo: Reuters)

In a statement on Tuesday, WHO Director-General Tedros Adhanom Ghebreyesus said that while it was understandable that all countries should want to protect their citizens, Omicron was still a largely unknown threat.

He added the world should not forget “that we are already dealing with a highly transmissible, dangerous variant – the Delta variant, which accounts for almost all cases globally”.

“We call on all member states to take rational, proportional risk-reduction measures,” the WHO chief said in a briefing on Tuesday.

First reported in southern Africa a week ago, Omicron has triggered global alarm. Some 56 countries were reportedly implementing travel measures to guard against Omicron as of Nov. 28, according to the WHO.