U.S. flight cancellations exceeded 2,800 for the Christmas weekend, disrupting travel on one of the busiest periods of the year as the omicron-fueled wave of COVID-19 cases triggered aircrew shortages.

A winter storm in the Northwest U.S. added to the mess Sunday, with 20% of the flights canceled at Seattle-Tacoma International Airport, according to data tracker FlightAware.com as of 6 p.m. New York time. JetBlue Airways Corp. and Alaska Air Group Inc. each dropped more than 10% of their flights Sunday; a day earlier, JetBlue, Delta Air Lines Inc. and United Airlines Holdings Inc. had all pulled back on at least 12% of their schedule. The U.S. cuts on Christmas Day alone totaled more than 900.

Airlines’ tie-ups added to evidence of economic disruptions from the omicron variant, whose fast spread is causing havoc even though initial indications suggest that it causes less-severe illness than other COVID-19 variants. Health care systems are being squeezed by a lack of staff.