Dutch border police have said they’ve arrested and detained a couple who left a coronavirus quarantine hotel and were trying to leave the country.

The couple, a man from Spain and woman from Portugal according to Dutch media reports, had been asked to quarantine after one of them tested positive for Covid on arrival in the Netherlands on a flight from South Africa.

The couple left their designated Covid hotel on Sunday, however, and were arrested on a plane in Schiphol Airport in Amsterdam just before it departed for Spain.

The Royal Netherlands Marechaussee, a national police force in the Netherlands, said on Twitter Sunday that it had “arrested a couple this evening who had fled from a quarantine hotel. The arrests took place in a plane that was about to take off. Both persons have been transferred to the GGD” the police said, referring to the municipal health service.

Amsterdam daily newspaper Het Parool reported that the couple left the hotel in the Kennemerland region in the northwest of the country around 6 p.m. on Sunday with security guards alerting the Marechaussee of their departure. 

Shortly afterward, they were arrested on the plane “almost silently and without violence,” according to a spokesman for the police.

The Public Prosecution Service will later determine whether the couple will be prosecuted, the paper added. It’s unclear whether one of the couple infected with Covid tested positive for the omicron variant, which was dubbed “of concern” by the World Health Organization last Friday.

Still, the couple’s arrest comes as the Netherlands — a country already struggling with a surge in Covid cases and pressure on its health service — is on high alert for omicron cases after a handful were found among people traveling to the country from South Africa, where the variant was first discovered.

On Friday, a total of 624 passengers who arrived at Schiphol from South Africa were tested for the coronavirus by health officials. Of those, 61 tested positive for the virus and 13 of those people were found to have the omicron variant, according to the Dutch public health authority, or RIVM.

It has called on all visitors from South Africa, Botswana, Malawi, Lesotho, Swaziland, Namibia, Mozambique and Zimbabwe to get tested, regardless of whether they have symptoms or not. The South African doctor that first spotted the omicron variant said the symptoms she’d seen in her patients were extremely mild, making it potentially easier to miss.

Read more: South African doctor who first spotted the omicron Covid variant explains the symptoms

The Netherlands is not the only country to have detected cases of the variant. Cases have been found in several southern African countries (the variant was first spotted in South Africa) and also in the U.K., France, Israel, Belgium, Germany, Italy, Australia, Canada and Hong Kong, but none yet in the U.S.

There are several big unknowns regarding the variant, the WHO said on Monday. First of all, experts don’t know yet just how transmissible the variant is and whether any increases are related to immune escape, intrinsic increased transmissibility, or both.

Read more: Omicron Covid variant poses ‘very high’ global risk and is likely to spread, WHO warns

Secondly, there is uncertainty over how well vaccines protect against infection, transmission and clinical disease of different degrees of severity, and death. And third of all, there is uncertainty over whether the variant presents with a different severity profile.

The WHO has said it will take weeks to understand how the variant may affect diagnostics, therapeutics and vaccines. Preliminary evidence suggests the strain has an increased risk of reinfection, however.