Cases of the Omicron variant of the coronavirus were reported in the United Kingdom, Germany, Italy, and the Czech Republic a day after it was declared a variant of concern by the World Health Organization.

Omicron, designated is potentially more contagious than previous variants, although experts do not know yet if it will cause more or less severe COVID-19 compared with other strains.

The variant was first discovered by scientists in South Africa and has also since been detected in Belgium, Botswana, Israel and Hong Kong.

The two Omicron cases found in the UK on Saturday were connected to travel to southern Africa, British Health Minister Sajid Javid said.

“We will require anyone who enters the UK to take a PCR test by the end of the second day after their arrival and to self-isolate until they have a negative result,” UK Prime Minister Boris Johnson told a news conference.

The health ministry in the German state of Bavaria announced on Saturday two confirmed cases of the Omicron variant.

The two people entered Germany at Munich airport on November 24, before Germany designated South Africa as a virus-variant area, and were now isolating, the ministry said, indicating without stating explicitly that the people had travelled from South Africa.

A hospital in the northern Czech city of Liberec has confirmed a case of the Omicron strain in a female patient, according to the Czech Television.

The Czech Republic is currently grappling with a spike in coronavirus infections making it one of the worst-hit countries in the world in terms of infections per capita.

In Italy, the National Health Institute said a case of the new variant had been detected in Milan in a person coming from Mozambique.

There was also concern in the Netherlands after 61 people tested positive for Covid-19 after arriving on two flights from South Africa on Friday. Further tests were under way to determine if any of them had the Omicron variant.