The highly mutated strain has fueled a massive increase in cases across the globe, with countries reviving lockdowns, thousands of flights canceled and cruise ships returning to port with Covid-infected passengers.

There is, however, a "belief that Omicron is going to be a nuisance but not a dire strait for the global economy -- at least not for long," said Briefing.com analyst Patrick O'Hare.

Wall Street stocks enjoyed another strong round, with major indices winning at least one percent and the S&P 500 powering to a second straight record.

Monday opened the historically strong seven-day post-Christmas stretch known on trading floors as the "Santa Claus rally," a period of low trading volumes and light news flow that usually sees stocks drift higher.

Since 1945, the S&P 500 has risen more than three out of every four years during this period, winning an average 1.2 percent, according to CFRA Research's Sam Stovall.

But leading airlines such as United and Delta dropped following mass flight cancellations due to infections or quarantines among airline and airport staff.

Eurozone markets closed higher, while Asian markets finished down. London and Hong Kong were closed for holidays.

"Investors are continuing to shake off concerns regarding the Omicron variant following reports that the risk of hospitalization is much lower compared to previous variants," said a note by Schwab analysts.

A study released on Sunday showed US consumers were in the mood to spend over the holiday season, with retail sales soaring 8.5 percent over last year.

Online sales were up 11 percent and in-store sales up 8.1 percent between November 1 and Christmas Eve, according to the Mastercard SpendingPulse study.

"Consumers splurged throughout the season," said Steve Sadove, senior advisor for Mastercard and former CEO of Saks Incorporated.