U.S. airlines canceled thousands of flights over the year-end holidays through early this year due to Covid infections among crews and a series of winter storms. United first cut some flights before Christmas.

JetBlue Airways was the first carrier to cut back its January schedule because of a surge in infection rates among crews, which was later followed by Alaska Airlines. American Airlines said it would do the same this week as Covid rates climbed among regional carriers.

The adjustments are the latest move by an airline to cope with the rapid spread of the omicron variant.

Kirby said in a memo published on the company’s website Monday that United is “reducing our near-term schedules to make sure we have the staffing and resources to take care of customers.” A spokeswoman on Tuesday declined to say how many flights the carrier is canceling.

United has about 3,000 workers who are currently positive for Covid, Kirby said in the staff memo. That is about 4% of its U.S. workforce.

“Just as an example, in one day alone at Newark [New Jersey], nearly one-third of our workforce called out sick,” Kirby said. He said that none of the carrier’s vaccinated employees, which make up more than 96% of its staff, are hospitalized and that it hasn’t had a Covid-related death among inoculated employees in eight weeks.

United on Dec. 31 offered triple pay for pilots to pick up trips through most of January. The pilots’ union said sick calls among aviators were at a record. Southwest Airlines also gave pilots incentive pay for this month.