Nearly 1 million Americans plan to fly to Florida over Labor Day weekend. An epidemiologist warns they could undo efforts to contain COVID-19 just before schools reopen.

• About 6 million Americans plan to fly this Labor Day Weekend, according to data from travel management app TripIt, and compared with TSA figures from 2019.
• That's far below 2019 numbers, but an unusually high proportion of those who have decided to fly are headed to Florida, Arizona, Nevada, and the Caribbean, all of which are struggling to rein in the COVID-19 pandemic
• An epidemiologist says we're at a critical stage in the pandemic, and that coronavirus outbreaks linked to travel could undo the progress that's been made just as schools are set to reopen.

Roughly 6 million Americans plan to fly during the upcoming Labor Day weekend, many of them to Florida and other "hotspot" areas struggling to contain the COVID-19 pandemic — despite CDC guidance saying the best way to protect oneself and others is to stay home.

Data collected by travel itinerary app TripIt show that while total flight bookings over the holiday weekend are down 66% compared to 2019, an unusually high proportion of those who have decided to fly over the holiday are headed to Florida, Arizona, Nevada, Mexico, and the Caribbean, all of which are struggling to rein in the COVID-19 pandemic.

Those beach retreats and weekends in the sun, however tempting after months of monotony, lockdowns, and quarantines, threaten to roll back progress at a critical moment in America's fight against the pandemic.

Florida had the second-most coronavirus cases in the country as of Tuesday, behind California, with 542,790 cases confirmed. The state set a new record for daily deaths on Tuesday, with 276. Arizona has begun to see case increases slow after spiking in June, but has the highest number of pediatric COVID-19 cases per capita in the US. In Las Vegas, casinos are open at 50% capacity, although Nevada has one of the country's highest rates of new infections.

About 12% of Labor Day air travelers are headed to Florida, TripIt said, compared to 4% in 2019. Based on TripIt and previous TSA data, that suggests about 720,000 Americans will fly to Tampa, Miami, Fort Lauderdale, Orlando, Fort Myers, Key West, Panama City, and other parts of the Sunshine State.

Several destinations in the Caribbean, Mexico, and Hawaii will also see an increase in travelers, the TripIt data show. Most locations in the Caribbean and Mexico require visitors to show proof of a negative COVID-19 test within 72 hours of departure, while Hawaii plans to implement a similar requirement starting September 1.

Tripit's numbers don't include anyone who travels by train, bus, or car. And in an unpredictable time, plenty of people may cancel — or book — a trip at the last minute.

The idea of so many out-of-staters headed to Florida and other areas fighting the virus raises serious concerns.

"There's potential not only for people to go to these regions and pick up COVID-19 and bring it back, but also to potentially exacerbate the pandemic in these hotspots," said Dr. Spencer Fox, an epidemiologist at the University of Texas at Austin. "We're at a critical time in the pandemic."

"Anything, like extra travelers, or activities going on, could potentially take you right back to the point where you were at the healthcare capacity surge."

Epidemiological models have shown that events like university reopenings, which bring 20,000 to 50,000 people together in a new location, can exacerbate a pandemic, Fox said. That suggests any travel influx could do the same.

"What happens ultimately depends on how risky those people are when they travel," Fox said. "If they treat it like a normal vacation and aren't taking any precautions that would be recommended to reduce transmission, it could very well exacerbate local pandemics, and then mean that they bring the disease back to wherever they're from."

Caribbean nations, meanwhile, have struggled to keep the number of cases low while avoiding the economic repercussions of banning American tourists. Some nations, like the Bahamas, have repeatedly eased restrictions, seen cases rise, and tightened them again. With strict testing protocols in place for entry, Fox said he was hopeful that these countries would be able to contain the potential spread of the coronavirus during Labor Day weekend.

With many schools and universities set to reopen in the next few weeks, Fox said now is an especially critical time for vigilance.

"There's a lot of potential for increased transmission in the next few weeks as this happens," he said. "It's just important for people to continue taking as many precautions as they can really."

Of course, Fox suggested, the safest move is to listen to the CDC: Do your best to enjoy one more long weekend at home.