• U.S. airlines have canceled hundreds of flights over the Christmas holiday, citing an increase in Covid cases among crews.
• Airlines offered flight crews extra pay to pick up trips.
• Carriers have asked the CDC to lower its recommended quarantine period for fully vaccinated staff.

Airlines have canceled more than 2,000 flights since Christmas Eve as the rapid spread of the omicron variant of Covid-19 drove up sick calls from flight crews.

The staffing shortages disrupted travel for thousands of customers, many of whom skipped holiday travel last year.

Airlines expect the year-end holiday period to include some of the busiest days since the pandemic began. The Transportation Security Administration screened 13.6 million people over the last week through Sunday, nearly double the number from a year ago but around 15% lower than in 2019, before the pandemic.

Carriers including United Airlines, Delta Air Lines, American Airlines and JetBlue Airways cited the spread of omicron among crews as a reason for the cancellations, while bad weather also played a role.

Other industries, including live entertainment and restaurants, have struggled with staffing due to rising Covid infections recently.

"Our current pilot Covid-19 case count is on the rise," Bryan Quigley, United's senior vice president of flight operations, wrote Sunday in a message to pilots, which was seen by CNBC. "Pilots who have developed symptoms are also in quarantine and we have a high number of pilots on the sick list."

U.S. airline shares fell on Monday after the cancellation reports.

On Monday, airlines had canceled more than 800 U.S. flights, an improvement from the 1,500 they scrubbed on Sunday but a sign the problems were continuing into the week.

United canceled 87 Monday flights, or 4% of its mainline schedule, down from 118 a day earlier, according to flight-tracking site FlightAware. Delta canceled 64 flights Monday, compared with 189 Sunday. Alaska Airlines canceled 98 flights Monday, while regional carrier SkyWest dropped close to 200 flights.

Airlines encouraged travelers to check their carrier's website and apps for flight information. Carriers say they try to inform travelers of cancellations as early as possible so customers don't make unnecessary trips to the airport.

Bigger schedules

Airlines ramped up their schedules ahead of the holiday to cater to high demand.

"During the course of the pandemic, when our numbers rose, we were able to absorb the flying because we had a significantly reduced schedule," United's Quigley wrote to pilots. "Now as we approach 2019 flying levels, we must do all we can to ensure we are protected so that we can fly the schedule.

U.S. airline executives last week asked the Centers for Disease Control and Prevention to halve quarantine guidelines for fully vaccinated individuals who test positive for Covid to five days from the current 10, citing potential staffing shortages and flight disruptions. The CDC eased its guidelines for health-care workers with breakthrough Covid infections last week.

New York State health officials shortened the quarantine period for essential workers with breakthrough Covid cases to five days.

"If you meet this criteria and are eligible to return to work after 5 days of isolation, you must otherwise stay at home when not at work and continue to take basic precautions until the end of the standard 10-day isolation period," New York-based JetBlue said in an employee memo, which was reviewed by CNBC.

Extra pay

After staffing struggles in previous months led to mass flight disruptions at some carriers, airlines offered crews extra pay to work peak holiday periods and meet attendance goals.

A JetBlue spokesman said the New York-based airline entered the holiday season with the highest staffing levels since the start of the pandemic.

"Like many businesses and organizations, we have seen an increasing number of sick calls from Omicron," he said in a statement. "Despite our best efforts, we've had to cancel a number of flights, and additional flight cancellations and other delays remain a possibility as we see more Omicron community spread."

JetBlue trimmed its schedule ahead of time to avoid last-minute disruptions and also assigned managers to frontline operations if they are trained, the spokesman added.

Spirit Airlines canceled more than 93 flights on Saturday and Sunday and offered flight attendants double pay to pick up trips this weekend, their union said.