Omicron cases discovered on flights into Amsterdam as scientists race to evaluate new threat

Dutch health officials said Sunday they had found at least 13 cases of the omicron coronavirus variant among 61 infected passengers who had arrived in the Netherlands from South Africa on Friday. The new cases were a clear sign that the virus was crossing borders even as governments imposed new travel restrictions and flight bans.

Additional cases could emerge, as health officials were still examining test samples, said Hugo de Jonge, the country’s health minister, adding that the people who tested positive were isolating. The 61 passengers who had tested positive were among more than 500 who arrived on two separate flights.

A growing list of countries is scrambling to respond to the new, highly mutated version of the virus, which was first detected in Botswana and South Africa and which has sent ripples of panic through governments and markets. Health officials in Australia and Denmark on Sunday both confirmed cases of the omicron variant in travelers recently arriving from southern Africa.

And British health officials said Sunday a third case had been detected in an individual who had spent time in Westminster, in central London. They said the case was linked to travel to southern Africa.

The World Health Organization warned Friday that omicron was a “variant of concern,” the most serious category the agency uses for such tracking, and said that its numerous genetic mutations could help it spread more quickly, even among vaccinated people.

Scientists cautioned that relatively little is known about the new variant and that only a small number of confirmed cases have surfaced globally.

In Australia, officials said that omicron was detected in two travelers who flew into Sydney on Saturday evening on a Qatar Airways flight from Doha. They were asymptomatic and fully vaccinated, according to a statement from the health authority in New South Wales state. The travelers were placed into quarantine.

In Denmark, officials said that omicron was detected in two travelers who had recently arrived from South Africa. Both are in isolation, and their close contacts are being tracked down, according to a statement by the State Serum Institute, Denmark’s infectious disease authority.