▶ Watch Video: Holiday travel approaches pre-pandemic levels

United and Delta have canceled more than 200 flights on Christmas Eve as a surge in COVID-19 cases impacts their staff, the airlines said Thursday. The cancellations come as the Transportation Safety Administration says the number of people traveling for the holiday is returning to pre-pandemic levels.

“The nationwide spike in Omicron cases this week has had a direct impact on our flight crews and the people who run our operation,” a United Airlines spokesperson told CBS News in a statement. “As a result, we’ve unfortunately had to cancel some flights and are notifying impacted customers in advance of them coming to the airport.” 

As of now, the airline is proactively planning for 120 cancellations on Friday. A spokesperson for Delta Air Lines told CBS News that it too was planning to cancel around 90 flights on Friday. 

“Delta teams have exhausted all options and resources — including rerouting and substitutions of aircraft and crews to cover scheduled flying — before canceling around 90 flights for Friday” the airline said in a statement. 

Both airlines apologized for the disruptions. 

American and Southwest Airlines told CBS DFW Thursday they have no plans to cancel any flights due to COVID-19 staffing issues.

The United and Delta cancellations come as millions of people are expected to travel for the holidays. The TSA said its agents screened more than 2 million people on Wednesday, exceeding the number of travelers on that day in 2019.

The Centers for Disease Control and Prevention urges those planning to travel to be fully vaccinated against COVID-19. People are also advised to avoid crowded and poorly ventilated spaces and to wear a face mask when in public indoor settings. 

The CDC has also warned of spiking COVID-19 cases as the fast-spreading Omicron variant infects many throughout the nation. Omicron has become the dominant strain of the virus in the U.S. and health officials are urging people to get fully vaccinated and boosted.