WASHINGTON, Dec 26 (Reuters) - U.S. airlines called off more than 1,000 flights on Sunday as crews were grounded amid surging COVID-19 infections, causing misery for thousands of Christmas travelers. Commercial airlines had canceled 1,001 flights within, into or out of the United States by mid-afternoon, according to a tally on flight-tracking website FlightAware.com. It was the third straight day of traveling pain and further cancellations were likely as COVID-19 infections have soared, driven by the highly transmissible Omicron variant. A total of 997 flights were scrapped on Christmas Day and nearly 700 on Christmas Eve. Thousands more were delayed on all three days. Enjoli Rodriguez, 25, whose Delta Air Lines Inc. (DAL.N) flight from Los Angeles to Lexington, Kentucky, was canceled 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 canceled 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. 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 that it 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. Poor weather in some areas also contributed to the problems. "Winter weather in portions of the U.S. and the Omicron variant continued to impact Delta’s holiday weekend flight schedule," a spokesperson for the airline saidin an emailed statement, adding that it was working to "reroute and substitute aircraft and crews to get customers where they need to be as quickly and safely as possible." A White House official, who asked not to be named, said that 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." Travelers are seen at Hartsfield-Jackson Atlanta International Airport in Atlanta, Georgia, U.S. December 22, 2021. REUTERS/Elijah Nouvelage/File Photo Passengers line up at John F. Kennedy International Airport during the spread of the Omicron coronavirus variant in Queens, New York City, U.S., December 26, 2021. REUTERS/Jeenah Moon A screen showing cancelled flights is seen at John F. Kennedy International Airport during the spread of the Omicron coronavirus variant in Queens, New York City, U.S., December 26, 2021. REUTERS/Jeenah Moon 1/7 Passengers line up at John F. Kennedy International Airport during the spread of the Omicron coronavirus variant in Queens, New York City, U.S., December 26, 2021. REUTERS/Jeenah Moon Read More "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 2,617 flights were called off and more than 10,500 were delayed, as of 3:41 p.m. EST (2041 GMT) on Sunday. STRIKING INCREASE United Airlines had to cancel around 100 flights on Sunday, a spokesperson said, and added that the company was working to rebook the impacted passengers. "Importantly, 25% 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. Winter weather was another factor negatively affecting the flights. A spokesperson for Southwest Airlines said all of their cancellations were weather related. The U.S. airports most heavily impacted by the cancellations were in Seattle, Atlanta, Los Angeles, Dallas-Fort Worth and JFK International in New York. Omicron was first detected in November and now accounts for nearly three-quarters of U.S. cases and as many as 90% in some areas, such as the Eastern Seaboard. The average number of new U.S. coronavirus cases has risen 45% 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 iterations, health officials have maintained a cautious outlook and say much remains to be learned about the variant. New York"s acting state health commissioner Dr. Mary Bassett said the "striking increase" in hospitalizations of children with COVID that the state has recorded in the last three weeks showed urgent action was needed. All children older than 5 should be fully vaccinated, she said, while those under 5 should be shielded by ensuring those around them have protection through vaccination, boosters, mask-wearing, avoiding crowds and testing. "The risks of COVID-19 for children are real," Bassett said in a statement. The state"s health department said the increases were concentrated in New York City and surrounding areas where Omicron is spreading rapidly. It said that in the most recent week, no 5- to 11-year-old admitted to the hospital due to COVID was fully vaccinated. It did not give details on the overall number of hospitalizations, or the severity of the cases.