In early May, all U.S. airlines started requiring all passengers to wear a face mask in-flight, and by June, the airlines had agreed to start rigorously enforcing their mandatory mask policies—with good reason. The new policies were enacted after the U.S. Centers for Disease Control and Prevention (CDC) issued updated guidance on wearing face masks to help slow the spread of COVID-19, guidance that has recently been reinforced. The agency now strongly (this emphasis is new) recommends we all wear face masks in public settings where we can’t be socially distant, including on airplanes.
“COVID-19 spreads mainly among people who are in close contact with one another—within about 6 feet, so the use of masks is particularly important in settings where people are close to each other,” the CDC states.
According to the agency, mounting evidence continues to show that masks serve as a barrier “to preventing respiratory droplets from traveling into the air and onto other people.”
There has been less evidence collected regarding how much protection masks provide specifically on an airplane, which is an enclosed setting where maintaining a safe six feet of distance between passengers is nearly impossible.
Some recent studies are finally shedding light on the topic, including a September 25 report in the Journal of Travel Medicine, which compared COVID-19 transmission outcomes on flights where mask wearing wasn’t required to those where it was. The contrast is compelling.
On March 2, one person flying in business class on a Vietnamese Airlines flight from London to Hanoi had symptoms while flying and tested positive for COVID-19 on arrival. Out of the 21 passengers in business class on that flight, 12 ended up testing positive for COVID-19 within five days of arrival. Two passengers and one flight attendant in economy also ended up testing positive, for a total of 15 transmissions out of the 201 passengers onboard. Mask wearing was optional on that flight.
Compare that to data from a series of Emirates flights between June 16 and July 4 showing how Emirates’ mandatory mask policy may have helped prevent transmissions. Despite the fact that a total of 58 passengers on five flights lasting eight hours between Dubai and Hong Kong tested positive for COVID-19 on arrival in Hong Kong, there were zero transmissions among the 1,500 to 2,000 passengers total on those five flights, according to data collected in Hong Kong.
When analyzing some of the best documented in-flight transmission events, which includes the Vietnamese Airlines example above, “masking was not mandated in any way and, according to the published reports, was rarely practiced,” the report found.
“The absence of large numbers of confirmed and published in-flight transmissions of SARS-CoV-2 is encouraging but is not definitive evidence that fliers are safe,” the report concluded. “At present, based on circumstantial data, strict use of masks appears to be protective.”
The Journal of Travel Medicine article was followed by a study from the U.S. Department of Defense that, while thorough, had some skeptics raising their eyebrows due to the fact that some of the study’s partners have some skin in the game—they include United Airlines and Boeing. Nevertheless, the findings are noteworthy.
After conducting more than 300 aerosol-release tests using mask-wearing mannequins to simulate infected passengers on Boeing 767-300 and 777-200 aircraft, the Defense Department found that when a passenger is seated with a mask on, only 0.003 percent of infected air particles can enter that passenger’s breathing zone—even when the plane is completely full.
The study found that the rapid dilution of the aerosol is due to high air exchange rates in the aircraft, a ventilation system that circulates air downward, and HEPA-filtered air. HEPA, or high efficiency particulate air, filters are designed to remove the majority of airborne particles, according to the U.S. Environmental Protection Agency.
“While the tests did have some limitations, specifically [they] only considered a single infected passenger and did not attempt to gather data reflecting passenger movement about the cabin, the results are encouraging,” said commander Joe Pope, operations directorate liaison for the testing for the Defense Department’s U.S. Transportation Command. “The calculations show about 54 flight hours are required for cumulative inhalation of an assumed infectious dose.”
The study concluded that “the overall exposure risk from aerosolized pathogens, like coronavirus, is very low.”
The hope, according to the authors of the Journal of Travel Medicine study, is that these findings will serve as a springboard for additional research to be carried out so that we can continue to better understand how mask protocols on flights serve to protect fliers amid the coronavirus pandemic.
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