NEW YORK (AP) — Flight cancellations that disrupted holiday travel stretched into Monday. Staffers calling out sick because of COVID-19 have left airlines short in recent days. Airline tracker FlightAware says airlines have canceled more than 4,000 flights to, from or inside the U.S. since Friday, with over 1,000 U.S. cancellations on Monday. Delta, United, JetBlue and American have all said that COVID was causing staffing problems, and European and Australian airlines also canceled holiday-season flights because staff were out sick. Other factors such as weather have played a role as well. Flight delays and cancellations tied to staffing shortages have been common this year.