Airlines and airports are lowering expectations for Thanksgiving amid surging cases of COVID-19 nationwide.

The pandemic is worsening just ahead of one of the busiest times for air travel.

For months, U.S. airlines have pinned hope of a significant revenue boost on the holiday season. And while more Americans will be flying next week than have been in recent weeks, it's now being further restrained by the virus' uncontrolled spread.

"The situation remains dire for the industry," Nicholas E. Calio, chief executive of industry trade group Airlines for America (A4A), said Thursday. "Demand currently, with everything going on, is softening."

The Centers for Disease Control and Prevention on Thursday urged Americans to stay home for Thanksgiving, an escalation of its previous cautions on holiday travel.

The CDC is imploring, but not mandating, that people avoid travel to help prevent spreading the virus from one community to the next. The federal agency's guidance also contains a list of things people can do make any holiday travel as safe as possible.

Minneapolis-St. Paul International Airport is expecting passenger security checkpoint volumes to be down about 65% from last year for the Tuesday-Sunday Thanksgiving stretch. During non-holiday weeks, MSP's passenger levels are about 70% below normal.

In 2019, U.S. airlines carried about 31.6 million passengers during Thanksgiving week, according to A4A. This year's projections are far lower, with 40% fewer seats available on airplanes due to a reduction in flights. The booked revenue is even worse, Calio said, down 80% from last year on steeply discounted fares.

Twin Cities-based Sun Country Airlines' Thanksgiving bookings are down 40% compared to last year, the company said.

Delta Air Lines, the dominant carrier at MSP, declined to provide its current booking forecast but said it will have at least 40% fewer flights during the Thanksgiving peak than it did at the same time last year.

One of the greatest changes — and planning challenges — for airlines during COVID-19 is that people are waiting until the last minute to book flights.

The spread of the virus is always changing and people are waiting until closer to their departure date to make travel decisions. In September, for instance, half of all Sun Country's passengers booked their flights within the month.

"It continues to be difficult to predict as people are booking really close to travel — even for some of the long-haul, [international] stuff, which is unheard of," said Jessica Wheeler, a spokeswoman for Sun Country.

Within the past week, she said, the airline has seen an uptick in passengers canceling their Thanksgiving travels. Following the CDC's urgent request Thursday that Americans not travel, an A4A spokeswoman said the airline industry is now braced for many more flight cancellations and rebookings.

Airports, airlines and the U.S. Transportation Security Administration (TSA) are trying to prepare those who are flying next week for the first time since the start of the pandemic.

"We do expect [Thanksgiving] to be the busiest time we've seen since COVID hit," said Brian Ryks, chief executive of the Metropolitan Airports Commission (MAC), earlier this week at a MAC meeting. He said about 60% of the people flying for the Thanksgiving holiday have not flown since the virus hit last spring.

The air travel experience has changed over the last eight months, with TSA agents wearing personal protective equipment, acrylic barriers separating agents from passengers and much more frequent checkpoint cleanings, said TSA Administrator David Pekoske.

"The advice that we would give to travelers with respect to Thanksgiving week travel is to wear a mask," Pekoske said Thursday. "It is one of the best ways to prevent further spread of this disease and one of the best ways to protect themselves."

As of Thursday, the TSA said there are 557 active cases of its employees nationwide who have tested positive for the virus. Since last spring, 2,981 have tested positive, 2,424 have recovered and nine employees have died, including a longtime screener at MSP.

There have been 31 confirmed COVID-19 cases among TSA employees at MSP. The work date of the most recent confirmed case was Nov. 13.

"In general we're seeing an uptick in people exposed, but we don't know if it's from work or from outside of work," said Neal Gosman, a spokesman for Local 899 of the American Federation of Government Employees, which represents TSA workers.

As Thanksgiving approaches, he said TSA workers "are a little bit more nervous, but we're coming in to work. We're doing our jobs." Many are taking advantage of the free COVID-19 saliva testing at the airport's main terminal.

Most major U.S. airports, including MSP, and the airlines require mask usage throughout the terminal and aboard the aircraft.

The absence of a federal standard has led to a patchwork of local restrictions, which industry officials say puts the onus on travelers to research what is expected of them at their destination.

"It's important to understand the rules and restrictions of where you are traveling," said Kevin Burke, chief executive for Airports Council International-North America. "Know your role in ensuring health and safety ... and wear your mask."

Staff writers Janet Moore and Joe Carlson contributed to this report.

Kristen Leigh Painter • 612-673-4767

Correction: Previous versions of this article misstated the number of air travelers during Thanksgiving 2019. The number is 31.6 million.