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.

It was unclear if XBB.1.5 would cause its own wave of global infections. Current vaccines continue to protect against severe symptoms, hospitalisation and death, experts say.

“Countries need to look at the evidence base for pre-departure testing” and if action is considered, “travel measures should be implemented in a non-discriminatory manner,” Smallwood said.

That did not mean the agency recommended testing for passengers from the United States at this stage, she added.