(The Hill) — More than 1,800 flights within, into or out of the U.S. were canceled on Monday as airlines grapple with inclement weather and staff shortages due to COVID-19.

A total of 1,867 flights were canceled as of 8:20 a.m. ET on Monday, according to FlightAware. As of Monday morning, airlines had already issued 861 delays for flights within, into or out of the U.S.

Southwest canceled 437 flights, JetBlue reported 136 cancellations, United recorded 103 cancellations, Delta called off 78 flights and American Airlines canceled 36 trips, according to FlightAware.

Monday’s cancellations were the latest in a weeks-long saga of airlines being forced to cancel trips because of a nationwide surge in COVID-19 cases. Some airlines reported staff shortages because of the virus, forcing them to pare down the number of flights per day.

The U.S. is seeing a spike in COVID-19 infections driven in part by the omicron variant, which is more transmissible than previous strains of the virus.

More than 2,700 flights within, into or out of the U.S. were canceled on Sunday. More than 15,000 U.S.-flights have been canceled since Christmas Eve, according to USA Today.

Inclement weather conditions are also driving Monday’s flight cancellations. A winter storm slammed a part of the Midwest on Sunday and is now headed for sections of the East, according to USA Today.

Federal offices in Washington, D.C. are closed on Monday because of the wintry weather.

Undeterred by the cancellations and delays, travelers still made trips this weekend. The Transportation Security Administration said more than 1.6 million individuals passed through travel checkpoints on Saturday.