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 the omicron variant leaped ahead of other variants to become the dominant version of the coronavirus in the U.S.

The moves in Los Angeles and Rhode Island reflected widening fears of a potentially devastating winter COVID-19 surge. Much of the concern is being driven by omicron, which federal health officials announced accounted for 73% of new infections last week, a nearly sixfold increase in only seven days.

Omicron's prevalence is even higher in some parts of the U.S. It's responsible for an estimated 90% of new infections in the New York area, the Southeast, the industrial Midwest and the Pacific Northwest, federal officials said.

The announcement underscored the variant's remarkable ability to race across oceans and continents. It was first reported in southern Africa less than a month ago.

Scientists say omicron spreads more easily than other coronavirus strains, including delta, though many details about it remain unknown, including whether it causes more or less severe illness. But even if it is milder, the new variant could still overwhelm health systems because of the sheer number of infections.

Organizers of the New Year's Eve party planned for Grand Park in downtown LA nixed plans for an in-person audience, saying the event will be livestreamed instead, as it was last year. In Rhode Island, which has the most new cases per capita over the last two weeks, masks or proof of vaccination will be required in most indoor establishments for at least the next 30 days.

And in Boston, the city's new Democratic mayor announced to howls of protests that anyone entering a restaurant, bar or other indoor business will need to show proof of vaccination, starting next month. City employees will also be required to get vaccinated.

"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."

Erika Rusley, a 44-year-old Providence, Rhode Island, resident, says recent events prompted her family to pump the brakes on everyday activities.

The elementary school teacher and her physician husband pulled their two young daughters from swim lessons this week, limited their play dates and canceled medical appointments, even though the whole family is fully vaccinated.

"The past week or so we've really just shut things down. It's just not worth it," Rusley said. "We're back to where we were pre-summer, pre-vaccine. It's square one, almost."

In New York City, where a spike in infections is already scuttling Broadway shows and causing long lines at testing centers, Mayor Bill de Blasio is expected to decide this week whether the city's famous New Year's Eve bash in Times Square will come back "full strength" as he promised in November.

North of the border, the Canadian province of Quebec imposed a 10 p.m. closing time for restaurants, banned spectators from sporting events and shuttered gyms and schools and mandated remote work.

Across the Atlantic, the World Economic Forum announced Monday that it would again delay its annual meeting of world leaders, business executives and other elites in Davos, Switzerland.

But in Britain, Prime Minister Boris Johnson said Monday that officials decided against imposing further restrictions, at least for now.

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 weighing curfews and stricter social distancing requirements.

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

Johnson's warning throws 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 planned 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.

White House press secretary Jen Psaki said the president would issue a "stark warning" and make clear that unvaccinated individuals "will continue to drive hospitalizations and deaths," she said.

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

The country is averaging nearly 130,500 new COVID-19 cases a day, up from about 122,000 a day two weeks ago, according to Johns Hopkins University data.

In Texas, a hospital system in Houston reports that omicron already accounts for 82% of new symptomatic COVID-19 cases it is treating, a dramatic increase from Friday, when testing showed it was responsible for just 45% of the system's cases.

But in Missouri, an early epicenter of the delta surge, the variant still accounts for 98% to 99% of COVID-19 samples, according to the state's Department of Health and Senior Services.

Meanwhile, hospitals in Ohio have postponed elective surgeries, while governors in Maine and New Hampshire have sent in National Guard reinforcements to help beleaguered hospital staff in recent days.

In Kansas, rural hospitals are struggling to transfer patients, with some left stranded in emergency rooms for a week while they wait for a bed. Overwhelmed hospitals as far away as Minnesota and Michigan have been calling looking for beds in larger Kansas hospitals. Often there simply isn't room.

"It's already as crazy as it can be when you are talking about moving people from Minnesota to Kansas City for treatment," Dr. Richard Watson, founder of Motient, a company contracting with Kansas to help manage transfers, said Friday.

Still, many political leaders are reluctant to impose the stiff measures they resorted to earlier in the pandemic.

France is desperately trying to avoid a new lockdown that would hurt the economy and cloud President Emmanuel Macron's expected re-election campaign. The government in Paris, however, has banned public concerts and fireworks displays at New Year's celebrations.

Ireland has 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-19 pass checks.

For Rusley's family in Rhode Island, the news is worrying, but not enough to deter them from a trip to Denver to visit her husband's family.

They fly out after Christmas, but have decided they will spend extended time indoors only with vaccinated people this holiday season, something they would not have considered just a few months ago.

"We've been here before, and we know how to do this," Rusley said. "We're not going to be hiding in our house, but at the same time, we're not going to be taking unnecessary risks."

From The Associated Press