Several European countries have banned flights from the U.K. over fears about new coronavirus variant that has forced millions of people in Britain to cancel their Christmas plans.

Germany, the Netherlands, Belgium, Austria and Italy all announced restrictions on U.K. travel. Others will likely follow suit as scientists warned the new strain spread more quickly than its predecessor. With U.K. infection levels rising rapidly, Britain’s Prime Minister Boris Johnson told a Saturday news conference that London and the U.K.’s southeast would be put under the strictest lockdown rules, known as “Tier 4.”

As a result, nonessential shops, gyms, cinemas, hairdressers and bowling alleys will be forced to close for two weeks, while people will be restricted to meeting one other person from another household in an outdoor public space. A “bubble” policy — allowing up to three households to meet over the holiday period in parts of the country that are not under Tier 4 restrictions — will be severely curtailed and will only apply on Christmas Day, Johnson said.  U.K. health officials first identified the new variant, which British scientists have called “VUI – 202012/01,” in mid-September, Maria Van Kerkhove, the Covid-19 technical lead for the World Health Organization, told the BBC Sunday. It is “very common” for viruses to mutate, Simon Clarke, an associate professor in cellular microbiology at the U.K.’s University of Reading, told NBC News.

“When they cause an infection, they get inside our cells and take over the cell to make more copies of themselves to reproduce, and every time they do that a new set of genetic material was made for each new virus,” he said, adding that the new strain is “certainly fitter” than its predecessor.