WASHINGTON (NEXSTAR) – Despite travel warnings from the nation’s top health officials, more than three million Americans flew this weekend ahead of the Thanksgiving holiday, and airlines expect those numbers to increase even more by Wednesday, which is usually the busiest travel day of the year.

TSA reports its personnel screened about a million passengers each on Friday, Saturday and Sunday. That’s less than half the airline travelers compared to last year’s holiday but still a lot more than the nation’s top infectious disease expert would advise during a pandemic.

“People at airports. I mean, those are the things we’ve got to realize are going to get us into even more trouble,” said Dr. Anthony Fauci.

To avoid infection, Fauci plans on virtually celebrating Thanksgiving with his family this week but worries how the millions of Americans who are not following his lead will impact the country’s COVID-19 cases.

“When you get a crowded plane, you’re in a crowded airport, you’re lining up, not everybody’s wearing masks,” Fauci said. “That puts yourself at risk.”

Some of the busiest travel days are still to come: the Wednesday before Thanksgiving and the Sunday after. Fauci warns the country won’t realize the real toll of the holiday until weeks later.

“Things lag,” he said. “So what you don’t want to see is another spike in cases as we get colder and colder.”

Canada’s Thanksgiving last month may serve as a cautionary tale for Americans. Now six weeks later, the country’s cases have more than doubled from about 2,000 in mid-October to nearly 5,000, according to the Public Health Agency of Canada. It’s a spike that paints a potentially bleak picture for Christmas and New Year’s celebrations in the U.S.

“We’re in a very, very difficult situation at all levels,” Fauci said.