Face masks are an “essential protective measure” against COVID-19 during airline travel, according to the technical bulletin “Face Mask Use in Air Travel” released this week by Harvard’s T.H. Chan School of Public Health.

While the best protection while flying is a layered approach that includes mask use, HEPA filtration, and disinfected surfaces, universal mask compliance and correct use are a “critical” part of the equation, according to the report.

“The use of face masks is critically important throughout the air travel process, from entering the airport for departure to leaving the destination airport, because it diminishes the release of infectious particles into the environment,” the report says.

Major U.S. airlines have had face-covering policies in place since May and, in June, Airlines for America, the industry trade organization representing Alaska Airlines, American Airlines, Delta Air Lines, Hawaiian Airlines, JetBlue, Southwest, and United Airlines, announced that passengers could have their flying privileges revoked for not wearing face coverings on flights. Delta Air Lines said it has barred more than 300 customers from future flights for not complying.

When a symptomatic man and his pre-symptomatic wife, who both tested positive for COVID-19, wore masks when they flew on a 15-hour international flight with 350 passengers, no one else on the flight tested positive, according to the study.

A recent modeling study found that universal use of surgical masks on planes may reduce infection risk from respiratory particles to less than 1 percent, according to the report. When it comes to cloth masks, cotton fabrics with higher thread counts are most effective, researchers found. Cloth masks are between 58 to 83 percent effective in filtering particles of 1 µm aerosolized bacteria and 49 to 72 percent effective in filtering out particles containing .02 µm aerosolized viruses, according to the report.

“While face masks are imperfect barriers for droplets smaller than their filtration range, they can block larger droplets from entering the environment and evaporating into smaller, dense infectious particles that can be inhaled,” the study noted.

Travelers should avoid masks with valves or vents, which release unfiltered breath containing respiratory droplets and aerosols into the air, the report says. Masks with valves have been banned by major U.S. airlines. Also, it matters how masks are worn, according to the report, because they are less effective when the mouth and nose are not covered.

“Face masks of any kind without exhalation valves or vents help to prevent the spread of respiratory infectious diseases and should be worn by all people in public places as a mechanism to protect public health during the COVID-19 global pandemic,” the report says.

In the absence of a vaccine or treatment, masks are “one of the most pragmatic and effective options” for controlling the spread of the virus, according to the study.

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