BOSTON (AP) The nations second-largest city called off its New Years 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.

Omicrons prevalence is even higher in some parts of the U.S. Its 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 variants remarkable ability to race across oceans and continents. It was first reported in southern Africa less than a month ago.