LONDON >> Families must cancel their Christmas gatherings and most shops have to close in London and much of southern England, Prime Minister Boris Johnson said today as he imposed a new, stricter level of coronavirus restrictions on the region to curb rapidly spreading infections.

Johnson said today that the capital and other areas in southern England currently under Tier 3, the highest level of coronavirus restrictions, will move to an even stricter new Tier 4 that requires all non-essential shops, hairdressers and indoor leisure venues to close after the end of business hours today.

With just five days to go until Christmas, Johnson also announced that a planned easing of socializing rules that would have allowed up to three households to meet in “Christmas bubbles” from Dec. 23 to Dec. 27 , will be canceled for Tier 4 areas and sharply curtailed in the rest of England.

Households No mixing of households will be allowed in Tier 4 except under very limited conditions outside in public places. In the rest of England, people will be allowed to meet in Christmas bubbles for just one day instead of five, as the government originally planned.

“It is with a very heavy heart that I must tell you we cannot proceed with Christmas as planned,” Johnson said.

He said he concluded there was “no alternative open to me” and people must sacrifice this Christmas to have a better chance of protecting the lives of loved ones.

“I know how much emotion people invest in this time of year, and how important it is for grandparents to see their grandchildren,” Johnson said. “But when the virus changes its method of attack, we must change our method of defense.”

A fast-moving new variant of the coronavirus that is more than 70% more transmissible than existing strains appears to be driving the rapid spread in London and southern England, Johnson said. London now has the highest infection rates in England.

“There’s no evidence to suggest it is more lethal or causes more severe illness,” he stressed, or that vaccines will be less effective against it.

England’s chief medical officer, Chris Whitty, said the U.K. has alerted the World Health Organization that the new variant identified this week appears to be accelerating the spread of COVID-19. The government’s scientific advisers came to that conclusion based on preliminary modeling figures, and they are continuing to analyze the available data, he said.

Viruses mutate regularly, and scientists have found thousands different of mutations among samples of the virus causing COVID-19. But many of these changes have no effect on how easily the virus spreads or how severe symptoms are.

Maria Van Kerkhove, WHO’s technical lead on COVID-19, told reporters after receiving notification from England this week that the U.N. health agency had “no evidence this variant behaves differently” and that it was similar to a variant initially reported among mink in Europe. She said scientists would study the virus strain to see if there might be any difference in how it prompts an immune response in people.

Wales and Northern Ireland, which have their own devolved governments and independent rules for controlling the virus, have already announced fresh lockdowns once Christmas is over.

U.K. officials reported another 28,507 confirmed cases on Friday, and 489 deaths of people within 28 days of testing positive for the virus. The U.K. has Europe’s second-highest COVID-19 death toll behind Italy, standing at 66,541 as of Saturday.