Hundreds of flights in the United States and thousands around the world were canceled on Sunday as the Omicron variant of the coronaviruses affected crews during one of the busiest weekends for travel.
More than 750 flights with at least one stop in the United States and roughly 10 times as many around the world had been canceled as of midday Sunday.
On Christmas Eve and Christmas Day, thousands of flights were canceled. Many people fly to spend the Christmas holiday with their families, so the cancellation could disrupt travel plans. The number of people passing through security on Christmas Eve and Christmas Day was double that of last year, according to the Transportation Security Administration.
By midday on Sunday, 10 percent of JetBlue flights, 5 percent of Delta Air Lines flights, 4 percent of United Airlines flights and 2 percent of American Airlines flights had been canceled.
A spokesman for the airline confirmed the number of canceled flights reported by FlightAware. He said that the holiday season saw the highest staffing levels since the start of the Pandemic and that the airline had seen an increase in sick calls.
A United spokeswoman confirmed that there were 100 canceled flights.
A spokeswoman for Delta said Sunday that the company had canceled 161 flights and was expected to cancel 40 more on Monday. The Omicron variant and winter weather are what Delta attributed to the flurry of canceled flights.
A spokesman for American Airlines referred an inquiry to FlightAware.
Dan Landson, a Southwest spokesman, said that Southwest Airlines canceled 56 flights because of weather. He said in an email that there had been no operational issues related to Covid. Southwest is one of the four largest US carriers.
The United States is experiencing a rise in Covid cases as the Omicron variant is the dominant form of the virus. The average daily case load on Christmas is 201,000, which is more than the average case load during the summer season.
The Centers for Disease Control and Prevention recommends that employees who test positive for a vaccine-preventable disease be isolated for at least five days before they can return to work.
The C.D.C. would alleviate some of the staffing pressures and set up airlines to help millions of travelers returning from their holidays. The flight attendants union wants that the reduction in recommended isolation times should be decided by public health professionals.
