Effects rippled worldwide, with about 3,000 flights already cancelled Monday and 1,100 more on Tuesday, according to flight tracker FlightAware, reported NDTV.
Opening the way for more people to return to work sooner and minimizing the prospect of mass labor shortages, the US Centers for Disease Control and Prevention on Monday halved the isolation period for asymptomatic Covid-19 cases from 10 to five days in a bid to blunt mass Omicron-induced disruption.
The guidelines, which are non-binding but closely followed by US businesses and policymakers, further suggest that the five-day isolation period be "followed by five days of wearing a mask when around others."
Cases in the United States are already on track to reach record highs in January, fueled by large pockets of unvaccinated residents as well as lack of access to quick and easy testing.
President Joe Biden on Monday said that some US hospitals could be "overrun" but that the country is generally well prepared to meet the latest surge and Americans need not "panic."
In a virtual meeting with state governors and top health advisors, Biden stressed that the rapid spread of Omicron would not have the same impact as the initial outbreak of Covid-19 or the Delta variant surge this year.
"Omicron is a source of concern, but it should not be a source of panic," he said.
Nationwide, the United States is closing in on the daily high of 250,000 cases recorded last January in the world's most affected nation, which has lost more than 816,000 people to the pandemic.