As coronavirus cases rise across the United States this winter, completing any air travel will be full of fraught decisions — which airlines still have social-distancing protocols, whether to lounge in the airport, and when (if ever) it’s safe to take off your mask. But longer flights and those that require a layover at another airport will be perhaps the most anxiety-inducing, as they prolong your window of risk for picking up the virus.

Recent studies on in-flight transmission of the coronavirus make clear that longer flights have been superspreader events; the longer a group of people is gathered, the higher the risk of the virus becoming airborne. But health experts have also warned travelers that airports and public transportation can facilitate the spread of the coronavirus, as well.

“The problem is not only the plane — it’s the airport, the transit before the airport, anywhere that gets crowded, really,” says Carlos Acuña-Villaorduña, an epidemiologist at Boston Medical Center with expertise in modeling the projected spread of viruses. “This is a respiratory virus, and it only needs close proximity to spread.”

So what is a traveler to do if the options are either boarding a long, potentially crowded flight or breaking up the journey with a precautionary layover?

Doctors say it depends but that one option will typically be better than the other. Here’s what to think about before a long flight during the coronavirus pandemic.

The argument for a direct, nonstop flight

Consider if you’re taking a flight that’s several or more hours long, similar to the seven-hour journey Irish researchers said this summer was linked to 59 cases in the country. Is it wise to reduce your time in a single air cabin by including a stopover at an intermediary airport, or is there greater risk in introducing another ground stop?

David Freedman, an infectious-disease expert at the University of Alabama at Birmingham who frequently reviews travel-related covid-19 studies, says the risky boarding and deboarding process almost always outweighs the benefits of breaking up the journey.

“If you change planes, you’re hitting one more airport. And there is a huge amount of risk in the airport, but boarding and deplaning is the riskiest part of that,” Freedman says. “So doing that process an extra time really increases the risk. … The only advantage of breaking it up would be that, if you’re sitting next to somebody on your flight who is infected, it would cut your odds in half.”

Freedman notes that there are no existing studies on the risk of a layover specifically, but researchers have often pointed out that airport spaces such as security lines and gates where passengers congregate could also be responsible for cases linked to travel.

Acuña-Villaorduña says research has signaled planes’ air filtration systems are more efficient than standard ventilation ones.

“If you need to do an international flight, the risk in the airplane itself is relatively low,” he says. “So stopping at an airport, being in lines again, that probably is introducing a risk that is higher than being in a plane.”

A study by the Department of Defense concluded that if passengers wear masks for the duration of a flight, planes’ high-efficiency air filtration systems are effective in preventing aerosol droplets from spreading to other passengers. However, the study does not account for movement in the cabin or passengers removing their masks.

Both Freedman and Acuña-Villaorduña say they personally would not split up a long flight with a layover if they needed to fly for several hours. But they would prefer the flight be on an airline that is blocking seats for social distancing, to decrease the risk of being seated near someone with the coronavirus.

Freedman, however, says there is a scenario in which he would consider inserting a layover.

The argument for a layover

Flights that are 14 hours are more, Freedman says, might be worth breaking up — under the right conditions. Those ultralong trips that introduce more exposure to others create a greater probability that some passengers will remove their masks to eat and drink. A recent study by New Zealand health officials found that an infected man on an 18-hour flight to the country spread the coronavirus to at least four other passengers.

Freedman also points out that longer flights have a much greater chance for onboard bathrooms to become contaminated with the coronavirus if anyone onboard is infected, since on a shorter flight more passengers are likely to avoid the lavatory altogether.

How long is long enough to warrant a potential layover? “Ten hours, I would definitely fly straight,” Freedman says. “But a super long haul of 14, 15 hours, I would really want to think about the intermediate airport.”

There are a number of factors to consider about a layover hub, including “How likely is it to be busy … how vigilant are they about their covid precautions?” Freedman advises researching any layover airport before choosing the stop, making sure it is not prone to delays or poorly ranked for cleanliness.

Airports most likely to be best for a pit-stop are those with reputations for being high-tech and efficient in their cleaning methods. Airport awards for cleanliness, for example, have primarily been given to those in Asia: Tokyo, Seoul, Singapore, and Doha, for example, are the cleanest airports, according to ratings by Skytrax.

Those are the airports, Freedman says, he would be comfortable stopping at to break up an extra-long flight. But, of course, very few Americans are likely to be flying so far during the pandemic.

Traveling during the pandemic: