Flying on Air Force One was risky from a health perspective last week. President Donald Trump may have been contagious with Covid-19. And at least one aide, Hope Hicks, who traveled with the president to Minnesota for a rally, has tested positive. She had mild symptoms and quarantined on the flight back to Washington, according to news reports.

The incident raises questions about how safe it is to fly, and whether renewed concerns about Covid might stall a recovery in air travel. But there are big differences between commercial flights and travel on Air Force One, which may go a long way to impacting contagion risk.

Perhaps the biggest differences: mask use and seating configurations. Face coverings have not been required on presidential flights, while they are mandatory on major passenger flights. There is face-to-face seating on Air Force One, and passengers can roam around various parts of the aircraft, potentially spreading the virus. That is very different than staying seated for the duration of a commercial light.

“Everyone on a passenger flight is forward-facing with people seated on either side, and the airflow is top-to-bottom. The dynamics are very different,” says Raymond James analyst Savanthi Syth.

But negative headlines about Covid tend to affect travel demand, usually with a week or two lag. Demand has been weakening as cases in the U.S. rose. And a major test is coming with the holiday season. “The big revenue drivers for the quarter are around Thanksgiving and Christmas travel,” Syth says. “That will drive the lion’s share of demand in the quarter, and it will be even more important this year.”

About 700,000 passengers a day are taking commercial flights, down from 2.2 million daily a year ago. But some airlines have curtailed schedules on signs that demand is looking weak over the next few months.

Southwest Airlines

(ticker: LUV) cut 38,000 flights in November and 55,000 for December, about 45% of its schedule over those two months.

“We recently adjusted our flight schedule for November and December to reflect the demand we’re seeing for travel, a process we’ve been continually undertaking throughout this year,” Southwest said in a statement.

Airlines have adopted rigorous cleaning and safety measures, and they are using HEPA air filters that recirculate cabin air every five to seven minutes, scrubbing it of more than 99.9% of particulate matter and microbes.

Airflow to a cabin is recirculated 20 to 30 times per hour, says the International Air Transport Association, an industry advocacy group. IATA says the risks on a plane are lower than in many other types of confined spaces, where HEPA filters aren’t used.

“If people are taking off their masks to eat and drink in a bar, that’s riskier than being in a plane, not moving, not talking, not moving around,” says Dr. Lin Hwei Chen, director of the Travel Medicine Center at Mt. Auburn Hospital and an associate professor at Harvard Medical School. “In terms of ventilation, the airplane may actually be lower risk.”

Several studies have documented clusters associated with air travel, but the studies have had limitations. A study that was published in Emerging Infectious Diseases concluded that 15 of 217 people on a flight from London to Hanoi, Vietnam, last March were likely infected in flight. The source was a woman in business class who was contagious, the researchers concluded.

But this was a 10-hour flight, and duration of exposure matters a great deal with contagion. Masks weren’t mandatory in March, and most of the infections were among passengers in and around business class. The study relied on contact tracing to determine who caught the virus. Some passengers took cruises and visited hotels afterward, and it’s unclear if they were infected on the flight.

The researchers weren’t able to genetically sequence the strain of virus to determine if it was identical in all cases. The epidemiological evidence was strong in the study, Chen says, but “if the virus had been sequenced, the study would have been even more reliable.”

An article in the Journal of the American Medical Association concluded that very few cases of Covid transmission in-flight have been confirmed worldwide—only about 42 in total. By comparison, a study of transmission on high-speed trains in China showed a rate of 0.3% among passengers. “Onboard risk can be further reduced with face coverings, as in other settings where physical distancing cannot be maintained,” the JAMA article said.

Yet Covid appears to be a relatively hearty virus that can survive on the skin. A study published in Clinical Infectious Diseases found that Covid-19 may survive for 11 hours on skin, nearly nine hours longer than the influenza virus. That means Covid could be transmitted to surfaces more extensively, though it is also easily killed with alcohol and rigorous hand washing.

Byron Jones, a mechanical engineering professor at Kansas State University and expert in aircraft environmental controls, says more data would be needed to accurately determine risks in flight.

“The bottom line is we don’t have the data to make a quantitative assessment of the risk,” he says. One positive is that airlines are reporting lower infection rates among crew members than other ground workers. But consumers may overestimate the effectiveness of good ventilation on planes, since there are so many other ways the virus can be transmitted.

Chen also says that more data is needed. “We need a very large series of flights or systematic public health data, but those have not been published,” she says. The Centers for Disease Control and Prevention has said it’s aware of 1,600 Covid cases on U.S. flights, but it hasn’t published estimates on in-flight transmissions, she points out. “There should be more information available when CDC analyzes those cases and their contacts,” she added.

Jones says he would take a commercial flight—with a lot of precautions: “I would get a good mask, eye covering, my own sanitary wipes, and a supply of hand sanitizer,” he says. “Do those things and I think you’d be fine, but if it’s a 10-hour flight, I can’t imagine that you wouldn’t be exposed. I would think twice about taking a really long flight.”

Write to Daren Fonda at [email protected]

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