Thousands of passengers across the US were stranded Monday on one of the busiest travel days of the year – as a surge in Omicron Covid variant cases swept through airlines and prompted severe staffing shortages.

       The travel chaos continued after days of similar problems plagued Christmas weekend. According to FlightAware, which tracks flight cancellations, airlines have canceled roughly 4,000 flights to, from or inside the US since Friday.

       Staff shortages as a result of sickness and exposure, as Omicron cases spike across the globe, were compounded by inclement weather in the Pacific Northwest.

       “Test positives among flight attendants have increased as cases have risen across the country with the Omicron variant,” Sara Nelson, international president of the Association of Flight Attendants-CWA, said in a statement. “We are reminding flight attendants to remain vigilant: mask up, sanitise hands regularly, and if they haven’t already, get boosted or vaccinated.”

       AFA-CWA represents 50,000 flight attendants at 17 airlines. It has pushed back against airline efforts to reduce the isolation period for vaccinated workers who get covid in order to ease staffing shortages.

       Recommended What are the new travel changes and how will rules work? Travel industry relief mixed with fury after government eases rules Which countries are on the green list?

       “Staffing remains tight as workers are hesitant to pick up voluntary overtime due to disruptive passengers,” Ms Nelson said.

       “Covid concerns, and Covid test positives during the busiest travel period of the year. We have negotiated holiday incentives to help with operational challenges but there’s only so far you can stretch people.

       “It’s also important to recognize that some of the cancellations and delays are weather related.”

       The Air Line Pilots Association, which represents more than 61,000 pilots at 37 US and Canadian airlines, did not immediately respond to a request from The Independent.

       Airlines have suffered immensely since the beginning of the pandemic, with travel down, staff furloughed and then employee pushback against vaccine mandates.

       According to data from the Transportation Security Administration, airline travel this holiday season jumped significantly from last year — on some days double the number of fliers or even more — but generally still short of 2019 levels, AP reported.