The rise of the omicron variant does not appear to be keeping travelers home for the holidays: More than 2 million passengers a day have passed through Transportation Security Administration checkpoints since Thursday, with even busier days expected ahead.

That leaves the number of people who traveled in 2020, when many stayed home, in the dust. And it means some travelers might be heading out on their first big trip since Christmas 2019.

Here's what those who are returning to the roads and skies - for the first time in years, or even just weeks - should be aware of.

Be extra cautious as omicron spreads

According to data gathered by The Washington Post, new daily cases have risen 23 percent in the past week. Projections from the Centers for Disease Control and Prevention say omicron was responsible for 73 percent of new cases between Dec. 12 and 18.

Chris Beyrer, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health, told The Post recently that the surge is "higher and faster than anyone anticipated." Travelers should consider what they would do in case of infection, and decide whether they can afford that risk.

Top infectious-disease specialist Anthony Fauci said Sunday that people who have been vaccinated and boosted "should be OK" to travel, as long as they take precautions, like keeping a mask on in places like airports.

"I think people just need to be prudent," he said. "Clearly when you travel, there is always a risk of increased infection; that just goes with respiratory illnesses."

But families with kids too young to be vaccinated, seniors or people who are immunocompromised should be extra careful or even avoid traveling, health experts say.

The CDC says in cases where multiple households are gathering, people should avoid crowded indoor spaces in advance and take a test before getting together. The same measures as always apply: wearing masks around unvaccinated or at-risk people, getting together outdoors or in well-ventilated areas and avoiding groups if you feel unwell.

Be prepared to hunt for tests

Pharmacies are seeing "incredible" demand for rapid home tests, and people are waiting for hours at testing sites. For those who didn't have test kits at home already, the search could be frustrating and fruitless.

Experts advise making an appointment for a test in advance, where the option is available. Search health departments in your city for available options, and scour the web for home tests that can be delivered. Many airports have testing sites, but lines can be long and the costs can be high.

Pharmacies continue to receive shipments, so people should keep checking in person and online even if a location is out. And don't forget the human network: Friends or family might have extra tests on hand, or be near a store that has more in stock.

Prepare for crowds

The Christmas travel season is already underway, but expect flying and driving to be increasingly busy leading up to the holiday, right after and again after New Year's Day.

TSA spokeswoman Lisa Farbstein said the agency expects to screen nearly 30 million people between Dec. 20 and Jan. 3.

The busiest flying days are expected to be Dec. 23 and Jan. 2, according to travel booking app Hopper. But don't expect the two days after Christmas to be a walk in the park either: United Airlines says it expects those days to be "fairly busy" as some people return home from Christmas visits and others head out for vacations over the New Year's weekend break.

AAA projects just over 100 million people will drive 50 miles or more from home this year between Dec. 23 and Jan. 2. In partnership with transportation analytics firm Inrix, the travel group says minimal congestion is expected on Dec. 25 and Jan. 1.

But the rest of the holiday period, the afternoon is probably the worst time to travel by car. A forecast says road trippers should head out after 7 p.m. on Dec. 23 and before 1 p.m. on Dec. 24. On New Year's Eve, the best times to leave are before 1 p.m. or after 5 p.m.

Don't hold up the security line

To keep from slowing down the screening process - and to reduce touch points - air travelers should be extra careful not to bring prohibited items in their carry-on.

"TSA recommends that travelers should start packing with an empty bag before they begin to pack to ensure that there are no prohibited items inside," Farbstein said in an email.

The agency recommended putting gifts in boxes or bags instead of wrapping them because anything that requires additional screening would need to be unwrapped. Snow globes larger than a tennis ball should go in a checked bag because of the amount of liquid they contain.

Traditional Christmas foods like cookies, candy canes, fruitcake and chocolate can be carried on, but anything liquid or spreadable - including preserves, eggnog, wine, syrup and champagne - has to be packed and checked.

Flying with pets? Make sure you know the rules

Back in 2019, travelers could fly with emotional support animals in the plane cabin for no charge - and without a carrying case stowed under the seat. But new federal rules, unrelated to the pandemic, allowed airlines to put much stricter pet policies in place.

Passengers who want to fly with their small pets now must pay a fee between $95 and $125 each way, depending on the airline, and keep the critter in a carrier that fits under the seat. Airlines typically only allow a certain number of pets per flight, so travelers need to say in advance that they are carrying on a canine or feline companion.

Brace for all the things that could go wrong

Laurie Garrow, a professor at the Georgia Institute of Technology in Atlanta who specializes in air travel, said travelers should game out every step of their trip and plan for unexpected complications.

She said some airport parking lots that were available before the pandemic haven't reopened, so the remaining lots could be full.

"If you didn't check the parking availability before you left home, you could find yourself getting to the airport without a place to park," she said in an email.

Travelers should also check rates for services like Uber or Lyft in advance to see if a cab or some other option would be cheaper. Ride-sharing prices have soared during the pandemic.

While the Thanksgiving holiday was spared major cancellations, travel industry observers warn that there is still potential for air travel meltdowns with some airlines flying reduced schedules and dealing with staffing shortages.

"Don't expect precision," Richard Aboulafia, an aviation analyst at Teal Group, told The Post this fall. "Be flexible. Allow slack."

Car rental companies have also been stretched after selling significant chunks of their inventory, leading to higher prices and fewer cars.

"When you land, you also want to think about how you get to your final destination," Garrow said.

The Washington Post's Natalie B. Compton contributed to this report.