The first cases of the Omicron coronavirus strain in the UK have been confirmed as suspected incidences of the highly infectious mutation are also feared in a number of countries across Europe.
The variant, which has been seen to spread quickly between people in southern Africa, has led to renewed international travel restrictions.
Germany and the Czech Republic both reported suspected cases, while in the Netherlands further tests are being carried out on 61 people who have Covid and were on a flight from South Africa.
In the UK, two linked cases and their households, one in Chelmsford, Essex, and one in Nottingham, are being retested and told to self-isolate while contact tracing is done.
"We don't know how effective our vaccines will be. But we have good reasons to believe they will provide at least some measure of protection," British Prime Minister Boris Johnson said.
It is still early days to know how serious the new variant will be but Mr Johnson was hopeful that a combination of testing, tracing and self-isolation, especially for people returning from 10 southern African countries will reduce infections in UK.
"We need to slow down the spread of this variant here in the UK, because measures at the border can only ever minimise and delay the arrival of a new variant rather than stop it all together," he said.
"We will require all contacts of those who test positive with a suspected case of Omicron to self-isolate for 10 days regardless of your vaccination status."
Face masks are again compulsory in shops and public transport, he said.
“Late last night I was contacted by the UK health security agency. I was informed that they have detected two cases of this new variant, Omicron, in the United Kingdom. One in Chelmsford, the other in Nottingham,” Health Secretary Sajid Javid said.
“We have moved rapidly, and the individuals are self-isolating while contact tracing is continuing.”
Many EU nations have also, like the UK, US, Japan and Australia, imposed restrictions on travel from southern Africa.
Belgium had the first confirmed case in Europe of the mutation, referred to as a variant of concern by the World Health Organisation, which was first discovered in South Africa.
In Germany, there is one suspected case in Hesse region – a patient who returned from South Africa.
“The Omicron variant has, with strong likelihood, already arrived in Germany,” said Kai Klose, Hesse social affairs minister.
The Czech Republic is examining a suspected case of the variant detected in a person who spent time in Namibia, the National Institute of Public Health said on Saturday.
In the Netherlands, Covid was detected among 61 passengers who arrived at Amsterdam’s Schiphol Airport on two flights from South Africa on Friday.
Further tests were taking place. The passengers were put into isolation.
The first case in Europe was in Belgium, a woman who returned from Egypt through Turkey.
The WHO said the new type, originally known as B.1.1.529 and subsequently renamed Omicron, was more transmissible than the common Delta strain.