Countries should consider recommending that passengers wear masks on long-haul flights, given the rapid spread of the latest Omicron subvariant of COVID-19 in the United States, World Health Organization (WHO) officials said on Tuesday.

In Europe, the XBB.1.5 subvariant was detected in small but growing numbers, WHO and Europe officials said at a press briefing.

Passengers should be advised to wear masks in high-risk settings such as long-haul flights, said the WHO’s senior emergency officer for Europe, Catherine Smallwood, adding: “this should be a recommendation issued to passengers arriving from anywhere where there is widespread COVID-19 transmission”.

XBB.1.5 – the most transmissible Omicron subvariant detected so far – accounted for 27.6% of COVID-19 cases in the United States for the week ended Jan. 7, health officials have said.