United Airlines and Delta Air Lines canceled dozens of Christmas Eve flights as Covid hit flight crews.

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

U.S. airline executives this week asked the Centers for Disease Control and Prevention officials to loosen quarantine guidelines for fully vaccinated individuals who test positive for Covid to five days from the current 10, citing potential staffing shortages and flight disruptions. The CDC loosened those guidelines for healthcare workers on Thursday.

United canceled more than 131 mainline flights scheduled for Friday, about 7% of its schedule, according to flight-tracking site FlightAware.

Delta canceled more than 90 flights, or 4% of Friday’s schedule, citing bad weather in the Salt Lake City and Seattle area, two of its hubs, and the impact of the fast-spreading omicron variant. More than 80 of Delta’s Saturday flights were canceled.

“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. “We apologize to our customers for the delay in their holiday travel plans. Delta people are working hard to get them to where they need to be as quickly and as safely as possible on the next available flight.”

More than 90% of Delta employees and more than 96% of United’s U.S. staff are vaccinated, the airlines have said.

The disruptions are fewer than the mass cancellations some airline customers faced this summer and fall as carriers including American and Southwest grappled with staffing shortages. Both of those airlines offered staff extra pay to work peak holiday trips and meet attendance goals.