Passengers traveling over the Christmas holidays have been hit by disruption around the world after airlines canceled more than 4,500 flights, according to a flight tracking website.

There was a surge of cancellations on Christmas Eve and Christmas Day as the fast-spreading variant of the Omicron coronavirus meant airlines could no longer occupy their flights.

The website of flight tracking company FlightAware showed that on Christmas Eve, a typically heavy day of travel, 2,175 flights around the world were canceled. About a quarter of it was in the United States. On Christmas Day, 1,779 flights worldwide and 402 more flights scheduled for Sunday were canceled.

The bulk of the cancellations came from five companies, with China Eastern canceling 474 trips while Air China 188 scrapped. United canceled 177 flights, Air India 160 and Delta canceled 150.

United said, “The nationwide surge in Omicron cases this week has had a direct impact on our flight crews and the people who run our operations. As a result, we unfortunately had to cancel some flights and inform affected customers in advance before they come to the airport. ”

Meanwhile, Delta said it had “exhausted all options and resources – including rerouting and swapping planes and crews to cover scheduled flights – before canceling around 90 flights for Friday.” The airline blamed the effects of the Omicron variant and weather conditions for the cancellations.

In response to the pre-holiday chaos, airlines have called for quarantine rules to be relaxed for vaccinated personnel.

Delta CEO Ed Bastian has asked the head of the United States Centers for Disease Control and Prevention (CDC) to reduce the self-isolation time for vaccinated individuals with breakthrough infections from 10 to five days. Airlines for America and JetBlue supported the request.

The airlines’ social media feeds were filled with frustrated passengers asking for help after a spate of cancellations on Christmas Eve due to the fast-moving Omicron variant.

@Delta Yes, really?! You cancel my Christmas Eve flight at 12:30 p.m. ?? I got up at 2am to go to the airport with my baby and husband and won’t see the cancellation until I get to the airport to check in my luggage, ”tweeted a passenger at the airline on Friday – one of several similar messages addressed to airlines that have had to cancel flights.

Despite the uncertainties and grim news around the world, millions of Americans continued their travel plans through a second pandemic cloudy Christmas season.

Moses Jimenez, an accountant from Long Beach, Mississippi, flew to New York with his wife and three children despite the recent torrent of coronavirus cases dashed their hopes of seeing a Broadway performance of Hamilton or visiting some museums .

Hamilton was one of a dozen productions to cancel shows this week because cast and crew members tested positive for Covid-19. Museums have been removed from the family’s itinerary because many now require a vaccination card and the two younger children are not eligible for the vaccination.

Jimenez, 33, said his family would make the most of roaming the city’s streets and parks while meeting relatives and friends.

“We really just wanted to get out of the house, really, to bring the kids into town for Christmas,” Jimenez told Reuters on Thursday at New York’s LaGuardia Airport.

New York planned to severely cap the number of people it allows in Times Square for its annual New Year’s Eve celebration in response to the surge in new coronavirus cases, capping the number to 15,000.