United AirlinesAnd Delta Air LinesCovid struck flight crews and canceled many Christmas Eve flights.

United released a statement Thursday saying that the nationwide Omicron surge this week had a direct effect on their flight crews as well as those who operate our operations. We’ve had to cancel some flights and we are notifying affected customers before they arrive at the airport.

This week, U.S. airlines executives contacted the Centers for Disease Control and Prevention to inquire about their plans. loosen quarantine guidelinesFor fully-vaccinated persons who have tested positive for Covid, the deadline is five days. This is to avoid flight disruptions or staff shortages. These are the CDC loosened those guidelinesFor healthcare workers, Thursday.

According to FlightAware, United cancelled more than 131 flights on Friday. This represents about 7% of the airline’s schedule.

Delta cancelled more than 90 flights (or 4%) Friday due to bad weather in Salt Lake City and Seattle, which are two of its hubs and the effects of the rapidly-evolving omicron variant. The cancellations of more than 80 Delta Saturday flights are not surprising.

The airline released a statement saying that Delta teams exhausted all resources, including the possibility of rerouting or substituting aircraft and crews in order to meet scheduled flying. They then cancelled around 90 flights on Friday. Our customers are deeply sorry for this inconvenience. Delta employees are committed to getting them there as soon as possible and safely on their next flight.

According to the airline, more than 90% of Delta’s employees are currently vaccinated and 96% of United staff in America have been vaccinated.

These disruptions are less than the massive cancellations that many airline customers experienced this summer and autumn as airlines like Southwest and American struggled to meet staffing needs. Each airline offered extra compensation to staff in order to meet peak holidays and reach attendance targets.