The Covid-19 surge across the US has taken a heavy toll on United Airlines.
About 3,000 United Airlines employees have tested positive with most off work.
In a single day during the holidays, almost one-third of workers called in sick at main hub Newark Liberty International Airport.
In a memo to staff CEO Scott Kirby detailed the impact to the business, which saw more than 2,500 flights cancelled over the holidays.
"Our frontline teams continue to put in a tremendous effort during what I know is an incredibly challenging and stressful time — the Omicron surge has put a strain on our operation, resulting in customer disruptions during a busy holiday season," Kirby said.
However, no vaccinated employees are hospitalized, Kirby said.
United’s vaccine mandate works, Kirby said.
"In dealing with Covid, zero is the word that matters — zero deaths and zero hospitalizations for vaccinated employees," he said.
"While I know that some people still disagree with our policy, United is proving that requiring the vaccine is the right thing to do because it saves lives."
Although the situation is gradually improving, United still cancelled 150 flights on Tuesday.
