About 21 million people entered full lockdown restrictions in London, southeast and eastern England and Wales Sunday to curb the spread of a highly infectious new strain of COVID-19.

For the record: The World Health Organization tweeted that it’s in “close contact” with British officials on the variant, as the Dutch government introduced a ban on passenger flights from the United Kingdom, effective Sunday morning through Jan. 1, after finding a case with the same strain in the Netherlands.

Driving the news: British Prime Minister Boris Johnson said Saturday although there’s “considerable uncertainty,” the new strain “may be up to 70% more transmissible” than the original version of the disease. England’s chief medical officer Chris Whitty said the strain accounted for over 60% of new cases in London over the past week.

• Johnson said during the news conference that an expected Christmas Day reprieve — a planned postponement of restrictions that would permit up to three households to convene in “Christmas bubbles” — would be canceled for Tier 4 zones.
• The move means London, southeast and eastern England moved from Tier 3 restrictions to Tier 4 restrictions from Sunday. Non-essential retailers must temporarily shutter to help combat the rapidly rising coronavirus infection rate.
• Wales First Minister Mark Drakeford said the country would also lock down from Sunday as “hundreds of people” had caught this new “more aggressive” strain, the BBC reports.

The state of play: The British government is urging people to stay home and advised people to work from home whenever possible.

• People will not be allowed to leave or enter Tier 4 areas, and residents are prohibited from traveling abroad.
• Nonessential retail, indoor gyms, leisure facilities and personal care services will close, but religious gatherings will be allowed to continue.
• Social gatherings must be limited, while people living in Tier 4 areas are strongly advised to remain within their own households.

What he’s saying: “It seems that the spread is now being driven by the new variant of the virus,” Johnson said.

• “Our advisory group on new and emerging respiratory threats, NERVTAG, has spend the last few days analyzing this new variant — there’s no evidence that it causes more severe illness or higher mortality, but it does appear to be passed on significantly more easily.”
• There’s no evidence to suggest the COVID-19 vaccine will be any less effective against the new variant, Johnson noted.
• “When the virus changes its method of attack, we must change our method of defense,” he added. “We have to act on information as we have it, because this is now spreading very fast.”

The big picture: Johnson held an emergency meeting with his Cabinet on Saturday to settle on the latest restrictions. British health officials have shared data on the suspected strain with the World Health Organization, the prime minister said in his announcement.

Worth noting: The new measures are effectively designed “to cut off the capital and its surrounding counties from the rest of England,” the New York Times writes.

• “They are the most severe measures the government has taken since it imposed a lockdown on the country back in March, and they reflect a fear that the new variant could supercharge the transmission of the virus as winter takes hold.”

By the numbers: The U.K. surpassed 2 million coronavirus cases on Sunday morning and had reported over 67,000 deaths, per Johns Hopkins University data.

• The nation reported 28,560 daily cases on Friday.

Editor’s note: This article has been updated with new details, including comment from the WHO, Drakeford, the Dutch government and Whitty, along with new coronavirus data.