(The Hill) — More than 7,300 flights were canceled or delayed in the U.S. on Sunday due to spikes of COVID-19 cases as many people sought to travel home from their Christmas holiday destinations, USA Today reports

Approximately 5,900 flights were delayed as the omicron variant has led to a surge in coronavirus cases nationwide. About 1,400 flights were canceled altogether, according to the news outlet, which gathered its data from the flight-tracking website FlightAware.  

The news of the mass delays and cancellations comes after around 4,000 flights had been delayed or canceled on Christmas on Saturday as airlines cite extreme staff shortages from COVID-19 infections.

American Airlines told The Hill on Christmas that “a number of COVID-related sick calls led us to make the difficult decision to precancel some flights scheduled for today,” despite its operation “running smoothly.”

On Sunday, the nation’s top infectious disease expert, Anthony Fauci, said that he would support domestic air travel vaccine mandates.

“Anything that could get people more vaccinated would be welcome,” Fauci said when asked about the mandates in an appearance on ABC News. 

The Canadian government already has similar measures of vaccine requirements for flights in place as the ones Fauci suggested.

In Canada, if someone is age 12 or older, they must be fully vaccinated in order to board domestic or international flights as well as to board trains.