Kirby attributed these numbers to United’s vaccine mandate, which went into effect last summer.

“Zero of our vaccinated employees are currently hospitalized,” Kirby said. “Since our vaccine requirement went into effect, our hospitalization rate has been 100x lower than the general population in the U.S.”

Last August, United became the first U.S. airline to impose a vaccine mandate, sending a message to corporate America that vaccine requirements may soon become the norm. By September, more than half of United’s 67,000 U.S.-based employees had been vaccinated, with the rest waiting for their first doses or facing periods of unpaid leave or termination. Ultimately, around 200 United employees were fired.

United has now gone eight straight weeks without a COVID-related death among vaccinated employees. Prior to the mandate, “more than one United employee on average *per week* was dying from COVID,” Kirby wrote.

But even with zero reports of serious disease or death, the contagiousness of COVID variants have led to more people contracting the virus and having to isolate. That includes airline employees, which has dramatically affected the flight schedules of major airlines. United canceled nearly 2,000 flights between Dec. 22 and Jan. 3, around 7% of its scheduled routes during that period, according to FlightAware, a flight data tracking service. Thousands of flights across the U.S. have been canceled in the postholiday period owing to the Omicron surge, airline staff shortages, and inclement weather, stranding countless passengers.

At a recent Senate hearing in December, Kirby defended United’s vaccination requirements from Republican criticism. 

“Our recovery efforts started by taking early and aggressive action to mitigate the impact of the virus on our employees and our customers, and as our industry always does, we put safety at the forefront,” he said.