British scientists were scrambling to work out whether a mutant strain of the coronavirus, which has been spreading rapidly in England this month, may be resistant to the crop of newly developed vaccines.

The strain was first identified on December 13 in the county of Kent in southern England, and initial analysis by government scientists suggests it is “growing faster than the existing variants.”

On Sunday, Italy, Austria and Belgium joined the Netherlands in banning air travel from Britain due to rising concerns over the new coronavirus variant. Other European countries were also considering whether to impose a flight ban.

The World Health Organization tweeted: “We’re in close contact with UK officials on the new #COVID19 virus variant. They’ll continue to share info & results of their analysis & ongoing studies. We’ll update Member States & public as we learn more about the characteristics of this virus variant & any implications.”

Speaking to Sky News Sunday, Britain’s health minister Matt Hancock said the new strain is out of control and urged Britons to behave as if they already have the virus, especially in London and southern and eastern England. “It [the new strain] is an enormous challenge, until we can get the vaccine rolled out to protect people. This is what we face over the next couple of months.”

British Prime Minister Boris Johnson held an unscheduled meeting of ministers Friday amid mounting alarm about the threat posed by the mutant strain, which has been named VUI-202012/01.

Johnson said at a press conference Saturday that there was no evidence so far to suggest vaccines would be any less effective against the new strain, but he added that “there is still much we don’t know.”

He noted the new strain is up to 70% more transmissible than prior strains.

London, southeast England locked down

The British leader announced a virtual lockdown for London and the southeast of England, with people urged to stay at home. All non-essential stores are now to close, and people should not enter or leave the British capital or large parts of southeast of England.

“We can’t continue with Christmas as planned” said Johnson, noting that a previously announced relaxation of rules for the holidays would be reversed. In London and southern England, households now can’t mix to celebrate Christmas. Elsewhere in the country, up to three households can mix but only for Christmas Day itself.

“I must stress how complicated it is to work out, in a situation where things might be growing for other reasons, to really put your finger on that it’s actually the virus that is doing it, but the evidence is pointing in that direction,” Ewan Birney, deputy director of the European Molecular Biological Laboratory, told the BBC.

Midweek, health minister Matt Hancock said the new strain may be associated with the faster transmission of the virus in the southeast of England and London, but there was “nothing to suggest” it caused a worse disease, or that it might be resistant to vaccines that have only just received approval in Britain and the U.S.

England’s chief medical officer, Chris Whitty, said Britain has alerted the World Health Organization about the fast transmissibility of the variant strain.

“There is no current evidence to suggest the new strain causes a higher mortality rate or that it affects vaccines and treatments, although urgent work is under way to confirm this,” he said in a statement.

Jeremy Farrar, a government adviser and director of the Wellcome Trust, Britain’s largest medical research endowment, warned Saturday of his concern. He tweeted: “The new strain of COVID-19 is worrying & real cause for concern & extra caution. Research is ongoing to understand more but acting urgently now is critical. There is no part of the UK & globally that should not be concerned. As in many countries, the situation is fragile.”

Johnson also held emergency talks with the first ministers of Britain’s devolved governments in Scotland and Wales.

“I attended a four-nation call earlier today to discuss serious concerns over the spread of a new Covid variant,” Wales’ First Minister, Mark Drakeford, tweeted.

Scotland’s first minister, Nicola Sturgeon, said she would be holding discussions with her Cabinet following the four-nation talks and “preventative action may be necessary” to curb the spread of the new strain.

The new variant includes up to 23 changes, including with the spike protein, which the virus uses to enter human cells that allow it to replicate. There have been many mutations in the virus since it emerged last year in Wuhan, China, with 4,000 mutations in the spike protein alone. Virologists say most mutations are insignificant and are part of the expected evolution of the virus, but some may lead to more efficient transmission.

According to the government’s scientific advisers, the new strain is fast becoming the dominant strain, and they say it might be present in other countries.

“Scientists are working extremely hard to work out what is going on,” Mark Walport, a member of the government’s Scientific Advisory Group for Emergencies, told The Times newspaper.

“But it does definitely seem possible that this transmits more easily. It will make the social distancing even more critical,” he added.

Government scientists say it could take two weeks for scientists to establish how the new strain reacts to vaccines, but virologists are hoping that the changes won’t diminish the efficacy of vaccines, which are designed to produce antibodies against many different parts of the spike protein.

Hospitals in England are seeing a record number of patients suffering from COVID-19, the disease triggered by the coronavirus. About 38 million people in England were under tough coronavirus restrictions before Saturday’s announcement. The new measures amount to a virtual lockdown, something Johnson had said just a few days ago he would do everything to avoid.

Johnson’s decision to cancel Christmas for much of England has prompted the fury of some lawmakers from his ruling Conservative party. Many have fulminated for weeks against what they see as heavy-handed government and a lack of parliamentary oversight.

“The changes must be put to a vote on the Commons at the earliest opportunity,” said Mark Harper, chairman of the Covid Recovery Group of Tory MPs who have criticized government handling of the pandemic.

Keir Starmer, leader of the main opposition party, Labour, accused Johnson of indecisiveness. He had been calling for tougher restrictions for weeks and had warned against relaxing Christmas rules.

“Millions of families across the country are going to be heartbroken by this news—having their Christmas plans ripped up. And I’m really frustrated because I raised this with the prime minister on Wednesday and he dismissed that and went on to tell people to have a merry little Christmas, only three days later to rip up their plans,” Starmer told British broadcasters.

British health authorities announced a further 27,052 confirmed cases of infection across Britain Saturday and 534 more fatalities.

In all, more than 66,541 Britons have died from COVID-19, just 4,500 short of the total British civilian death toll in World War II.