Countries should consider recommending that passengers wear masks on long-haul flights amid the rapid spread of Omicron’s latest sub-variant of COVID-19, the World Health Organization (WHO) said, Reuters and Agerpres reported.

In Europe, the XBB.1.5 subvariant has been found in a small but growing number of people, WHO officials said at a press briefing on Tuesday evening.

Passengers should be advised to wear masks in high-risk situations such as long-haul flights, said Catherine Smallwood, WHO’s European Emergencies Coordinator. This should be a warning to passengers arriving from any place where there is widespread spread of COVID-19, she added.

Experts are unsure whether XBB.1.5 will cause its own wave of infections worldwide, as current vaccines continue to protect against the risk of severe symptoms, hospitalization and death, experts say.

“Countries should review the evidence base for pre-departure testing,” and if measures are considered, “travel measures should be implemented in a non-discriminatory manner,” Smallwood said. That doesn’t mean the agency is recommending testing for passengers in the United States at this point, she added.

Among the measures that could be taken are genomic surveillance and the targeting of passengers from other countries, as long as it does not divert resources from domestic surveillance systems.

Other measures include monitoring wastewater at points of entry such as airports.