2020.10.16  Washington Post

A Defense Department study of the risk of catching the coronavirus on a packed commercial flight concluded that a person would have to be sitting next to an infectious passenger for at least 54 hours to receive a dangerous dose of the virus through the air.

Researchers concluded that, if passengers wear surgical masks continuously, very little of the virus spreads, because of how the air is circulated and filtered on the planes.

The study, which used a mannequin expelling simulated virus particles to determine how the virus spreads as an aerosol inside an aircraft cabin, had some limitations. But it offers a new way to try to understand the risks of flying during the pandemic.

In a briefing Thursday, the scientists and Defense Department officials involved in the study were careful to note those limitations, but they said the results were encouraging.

“Within the scope of the test, the results showed an overall low exposure risk from aerosolized pathogens like covid-19 on these aircraft,” said Vice Adm. Dee Mewbourne, the deputy commander of the U.S. Transportation Command.

Significantly, the study did not examine the risk posed by the virus spreading in larger droplets that people can spread when eating or talking. Nor did it look at risks involved in getting to the airport and waiting to board a plane.

There have been few studies looking at real-world cases, with scientists hampered by limited testing and contact tracing and the difficulty of pinning down the moment of infection with a virus that incubates over several days.

The research that has been completed tends to date to March, before the wearing of masks was widespread.

United Airlines, which donated flight time for the mannequin study, was less circumspect than the Defense Department officials, hailing the new research as “landmark.”

“Your chances of COVID exposure on a United aircraft are nearly nonexistent, even if your flight is full,” Toby Enqvist, the airline’s chief customer officer, said in a statement.

The research was led and funded by Transportation Command, which operates Patriot Express, a program that uses commercial planes to transport members of the military and their families. The command wanted to determine the risks of doing that during the pandemic.

The study, run at Dulles International Airport, was carried out in late August aboard Boeing 777 and 767 jets. Researchers placed a mannequin, wearing a mask and unmasked, in different places around the planes and released fluorescent particles designed to mimic the virus. The tests were conducted on the ground and in the air. In all, the study ran 300 tests.

The researchers, which included a team from the University of Nebraska, concluded that the virus was removed by the plane’s air filtering systems 15 times as fast as in a typical home and five or six times as fast as what is recommended for hospital operating rooms and patient isolation rooms.

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