Humeyra Pamuk, Joel Schectman

WASHINGTON, (Reuters) – Nearly 900 cancellations by U.S. Airlines on Saturday were the result of COVID-19-related infections. These are causing some crew members to become incapacitated, resulting in a disruption of plans for thousands of holiday travellers over Christmas weekend.

According to FlightAware.com, more than 880 Christmas Day flights including those within or outside the country were cancelled, up from 690 as of Christmas Eve. Around 800 flights were delayed.

Christmas is a busy time to fly, however, the spread of Omicron, a highly transmissible variant, has caused a rapid increase in COVID-19 infection rates, causing airlines to cancel their flights. Crew and pilots must be quarantined.

United Airlines cancelled 230 flights according to a spokesperson.

Maddie King, spokesperson for United said that the Omicron case spike this week had an impact on flight crews as well as those who manage our operations. The cancellations only made up about 1% of the 4,000 daily United flights in holiday season.

She said, “We’re working hard to book as many people as we can and send them off for holidays.”

FlightAware data indicated that Delta Air Lines, (NYSE:), had scrubbed 292 flights at 11:23 am EST (1623 GMT), while American Airlines spokespeople said they had had to cancel 90 domestic flights. A total of over 2,500 flights were cancelled and 4,200 more were delayed globally on Saturday.

American Airlines spokesperson said that “our operation had been smoothly running, but unfortunately there were a few COVID-related sick call leading us to make the hard decision to cancel some scheduled flights today.”

All airlines weren’t affected in the same way. Southwest Airlines (NYSE 🙂 spokeswoman said Saturday that no problems were reported with Southwest Airlines’ flights.

Omicron was discovered for the first time in November. It now accounts almost three quarters of all U.S. cases, and up to 90% in certain areas such as the Eastern Seaboard.

According to a Reuters count, the average number of U.S. coronavirus infections has risen by 45% to 179,000 each day in the last week.

Omicron may cause milder symptoms and less hospitalizations, according to recent research. But health officials remain cautious.

Americans scrambled to take COVID-19 exams in advance of Christmas and many continued with their travel plans.

U.S. officials stated that anyone who is fully vaccinated may travel on holiday.