Leisure air travel is booming, but with COVID-19 cases soaring in the U.S., the airline industry can expect a slowdown after Labor Day — and that might actually be a good thing.

Why it matters: Airlines have struggled to keep up with the unexpectedly strong rebound in travel demand this summer, with Spirit Airlines' chaotic, cancellation-filled episode last week as the most extreme example.

• "The industry needs a little time to breathe," says Brian Kelly, CEO of The Points Guy, a travel advisory website. "In all my years, I've never seen an airline completely melt down like Spirit Airlines."

Where it stands: About 2 million people per day are passing through TSA airport security checkpoints this summer, about 21 percent below 2019 levels, says Airlines for America.

• Domestic air travel is down about 13 percent, while international travel is down 39 percent. Business travel remains far below normal levels, but had been expected to start picking up in the fall after children return to school.

Yes, but: Amid a new surge in coronavirus cases, the Centers for Disease Control and Prevention is rapidly adding countries to its "Do Not Travel" list because of their "very high risk" of infection.

• New travel warnings were issued this week for France, Iceland, Aruba, Israel and Thailand, among others.
• Other popular destinations in the "very high risk" category — 74 countries in all — include Greece, Ireland, the United Kingdom, Portugal, Spain, the Netherlands and Costa Rica.
• Those who must travel to those countries should be fully vaccinated, the CDC says, and anyone traveling overseas must have a negative COVID test to re-enter the U.S.

Meanwhile, the European Union has not yet shut the door on American visitors, but that could change in the coming weeks.

Be smart: There are no domestic travel restrictions in the U.S., but if the CDC applied its own standard to individual states, 39 would be flagged as a "Do Not Travel" destination, Forbes reports.

• If Florida were a country, it would rank second in the world for new infections, and Louisiana would rank fourth, per Forbes.

The bottom line, per Kelly: "I'm still comfortable traveling to Europe, where the numbers are way lower, and the [mask] culture is much more in line with common sense.

• "For people to cancel their trips to Europe and travel somewhere in the U.S. instead doesn't make much sense."