BOSTON (AP) — The nation’s second-largest city called off its New Year’s Eve celebration Monday, and its smallest state re-imposed an indoor mask mandate as fears of a potentially devastating winter COVID-19 surge triggered more cancellations and restrictions ahead of the holidays.

Organizers of the New Year’s Eve party planned for downtown Los Angeles’ Grand Park say there will not be an in-person audience. The event will be live-streamed instead, as it was last year. In Rhode Island, a mask mandate took effect Monday for indoor spaces that can hold 250 people or more, such as larger retail stores and churches.

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And in Boston, the city’s new Democratic mayor announced to howls of protests and jeers that anyone entering a restaurant, bar or other indoor business will need to show proof of vaccination starting next month.

“There is nothing more American than coming together to ensure that we’re taking care of each other,” Mayor Michelle Wu said at City Hall as protesters loudly blew whistles and shouted “Shame on Wu.”

Across the Atlantic, British Prime Minister Boris Johnson on Monday said officials have decided against imposing further restrictions, at least for now.

“We will have to reserve the possibility of taking further action to protect the public,” Johnson said. “The arguments either way are very, very finely balanced.”

The conservative government re-imposed face masks in shops and ordered people to show proof of vaccination at nightclubs and other crowded venues earlier this month. It is also weighing curfews and stricter social distancing requirements.

Johnson’s warning threw into stark relief the unpalatable choice government leaders face: wreck holiday plans for millions for a second consecutive year, or face a potential tidal wave of cases and disruption.

In the U.S., President Joe Biden is set to address the nation on the latest variant on Tuesday, less than a year after he suggested that the country would essentially be back to normal by Christmas.

His top medical adviser, Dr. Anthony Fauci, made the rounds on television over the weekend, promising that the Democrat will issue “a stark warning of what the winter will look like” for unvaccinated Americans.

Cases are surging in parts of the U.S., particularly the Northeast and Midwest, though it’s not always clear which variant is driving the upswing.

In New York City, where the mayor has said the new variant is already in “full force,” a spike is scuttling Broadway shows and spurring long lines at testing centers, but so far new hospitalizations and deaths are averaging well below their spring 2020 peak.

The city is also weighing what to do with its famous New Year’s Eve bash in Times Square. Mayor Bill de Blasio has said a decision will be made this week about whether the event will come back “full strength” — with attendees providing proof of vaccination — as he promised in November. Last year’s bash was limited to small groups of essential workers.

Much about the omicron coronavirus variant remains unknown, including whether it causes more or less severe illness. Scientists say omicron spreads even easier than other coronavirus strains, including delta, and it is expected to become dominant in the U.S. by early next year. Early studies suggest the vaccinated will need a booster shot for the best chance at preventing an omicron infection but even without the extra dose, vaccination still should offer strong protection against severe illness and death.

Even if it is milder, the new variant could still overwhelm health systems because of the sheer number of infections. Confirmed coronavirus cases in the U.K. have surged by 60% in a week as omicron overtook delta as the dominant variant.

But many political leaders are reluctant to impose the stiff measures they resorted to earlier in the pandemic — often because they promised their people that vaccines would offer a way out of such restrictions, and it may be politically untenable to impose them again.

France, for example, is desperately trying to avoid a new lockdown that would hurt the economy and cloud President Emmanuel Macron’s expected re-election campaign.

In Britain, the government hopes vaccine boosters will offer more protection against omicron, as the data suggests, and has set a goal of offering everyone 18 and up an extra shot by the end of December. More than 900,000 booster shots were delivered on Sunday, as soccer stadiums, shopping centers and cathedrals were turned into temporary inoculation clinics.

U.S. vaccine maker Moderna said Monday that lab tests suggested that a booster dose of its vaccine should offer protection against omicron. Similar testing by Pfizer also found that a booster triggered a big jump in omicron-fighting antibodies.

But many scientists say boosters along are not enough and tougher action is needed.

The speed of omicron’s spread in the U.K., where cases of the variant are doubling about every two days, is decimating the economy in the busy pre-Christmas period.

Usually teeming theaters and restaurants are being hit by cancellations. Some eateries and pubs have closed until after the holidays because so many staff are off sick or self-isolating. The Natural History Museum, one of London’s leading attractions, said Monday that it was closing for a week because of staff shortages.

Other countries are warily watching the U.K., which reported 91,743 more lab-confirmed COVID-19 cases on Monday, close to the record high for a single day set last week.

The Dutch government began a tough nationwide lockdown on Sunday to rein in sharply rising infections. The World Economic Forum, meanwhile, announced Monday that it is again delaying its annual meeting of world leaders, business executives and other elites in Davos, Switzerland, because of omicron uncertainty.

But many European leaders have opted for something less.

France and Germany have barred most British travelers from entering, and the government in Paris has also banned public concerts and fireworks displays at New Year’s celebrations. Ireland imposed an 8 p.m. curfew on pubs and bars and limited attendance at indoor and outdoor events, while Greece will have 10,000 police officers on duty over the holidays to carry out COVID pass checks.

In Spain, the national average of new cases is double what it was a year ago. But authorities in the country with one of Europe’s highest vaccination rates are betting primarily on mandatory mask-wearing indoors and the rollout of booster shots, with no further restrictions planned.

Neighboring Portugal is telling most nonessential workers to work from home for a week in January, but the country has no other new measures in the pipeline.

Hendrik Wuest, governor of North Rhine-Westphalia, Germany’s most populous state, said more restrictions could be on the horizon shortly after Christmas.

“I don’t think big New Year parties can happen this year — unfortunately, again,” he added. “Omicron won’t forgive us any carelessness if we aren’t cautious.”