Omicron, weather ground more than 1,300 U.S. flights on Sunday

U.S. airlines called off more than 1,300 flights on Sunday as surging COVID-19 infections due to the highly transmissible Omicron variant of the coronavirus grounded crews and forced tens of thousands of Christmas weekend travellers to change their plans.

Commercial airlines cancelled 1,318 flights within, into or out of the United States on Sunday, according to a tally on flight-tracking website FlightAware.com.

It was the third straight day of travelling pain, after a total of 997 flights were scrapped on Christmas Day and nearly 700 on Christmas Eve. Thousands more were delayed on all three days.

Dr. Anthony Fauci, the top infectious disease official in the U.S., warned of rising cases in the country in the coming days and potentially "overrun...hospitals, particularly in those regions in which you have a larger proportion of unvaccinated individuals."

"It likely will go much higher," he said of the Omicron-driven surge even as U.S. President Joe Biden last week unveiled new actions aimed at containing the latest wave and continued urging vaccinations and other prevention strategies.

With rising infections, airlines have been forced to cancel flights with pilots and cabin crew needing to quarantine while poor weather in some areas added to travelers woes.

Enjoli Rodriguez, 25, whose Delta Air Lines flight from Los Angeles to Lexington, Ky., was cancelled on Christmas Eve due to COVID-related staffing shortages, was one of the thousands still stranded on Sunday.

Delta rebooked Rodriguez on an early afternoon flight that connected in Detroit, but that flight was delayed by hours, so she missed the connection to Lexington.

Speaking from the Detroit airport on Sunday, Rodriguez said she was surrounded by angry passengers, flustered airline representatives and families with young children in limbo as several flights were either cancelled or delayed.

"I've run into a lot of people sharing their horror stories here. We're all just stuck in Michigan, Detroit, heading different places," Rodriguez told Reuters. She was rebooked on a later flight to Kentucky that will hopefully end her sleepless, days-long journey.

Recent rise in COVID-19 infections

The Christmas holidays, typically a peak time for travel, coincided with a rapid spread of the Omicron variant. Infections have risen sharply in many parts of the country, with New York state's health department warning on Friday it had recorded a "startling" four-fold increase in COVID-19 hospital admissions for children under 18 since the week beginning Dec. 5.

With the surge in infections, airlines have been forced to cancel flights with pilots and cabin crew needing to quarantine.

"Winter weather in portions of the U.S. and the Omicron variant continued to impact Delta's holiday weekend flight schedule," a Delta spokesperson said in an emailed statement, noting that the company was working to "reroute and substitute aircraft and crews to get customers where they need to be as quickly and safely as possible."

When that was not possible, it was co-ordinating with impacted customers on the next available flight, the spokesperson said.

Thousands of flights cancelled, delayed globally

United Airlines had to cancel about 100 flights on Sunday, a spokesperson said, adding that it remained a small portion of the average 4,000 daily flights.

"Importantly, 25 per cent of customers whose travel was interrupted were able to rebook on flights that allowed them to get to their final destination earlier than they otherwise would have," United spokesperson Maddie King said in an email.

A White House official, who asked not to be named, said despite the mess at some airports, "we're in a better place than last Christmas" and noted that "only a small percentage of flights are affected."

"But any cancellations can be a pain and delay reunions with family and friends, so the Transportation Department and the FAA are monitoring this closely," the official said, referring to the Federal Aviation Administration.

Globally, FlightAware data showed that 2,252 flights were called off and more than 7,100 were delayed, as of 11.30 a.m. ET on Sunday.

Omicron was first detected in November and now accounts for nearly three-quarters of U.S. cases and as many as 90 per cent in some areas, such as the Eastern Seaboard.

The average number of new U.S. coronavirus cases has risen 45 per cent to 179,000 per day over the past week, according to a Reuters tally.

While recent research suggests Omicron produces milder illness and a lower rate of hospitalizations than previous variants of COVID-19, health officials have maintained a cautious note about the outlook.