NEW YORK -- A new study released Thursday shows that the risk of COVID-19 transmission is "virtually non-existent" during air travel when passengers wear masks.
The study, conducted by the Department of Defense in partnership with United Airlines, found that when seated with a mask on, "only 0.003% of particles actually made their way into another passenger's breathing zone." The results have yet to be peer-reviewed.
Researchers conducted more than 300 tests over 38 hours of flight time and 45 hours of ground testing during a six-month period.
Each test used a mannequin equipped with an aerosol generator that could mimic breathing and coughing. The generator released 180 million particles -- equivalent to the number produced by thousands of coughs -- with the mannequin's mask on and off.
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More than 40 sensors throughout the plane detected the droplets, representing other passengers who could potentially come in contact with the particles emitted.
The study revealed that masks drastically limit the rate of transmission when a passenger is seated. Researchers, however, did not attempt to replicate what would happen if an infected person stands up or moves throughout a cabin.
"I'm not standing here telling people that I know exactly what they should do. What I am telling people is if you are inclined to travel or thinking about air travel, there is a reason today, based on this independent study, that you can feel confident that you can travel safely," said Josh Earnest, CCO of United.
The DoD study reflected similar earlier studies that found that an airplane's unique airflow helps minimize risk. On a plane, air flows down -- not front to back -- helping limit person-to-person transmission. High-efficiency particulate air filters also eliminate 99.9% of airborne particles, including viruses, every two to three minutes.
"This study is confirming that you know among all the different places where one can get infected, flights might actually be one of the safest places to be," said Dr. Rajat Mittal, a professor of mechanical engineering at John Hopkins University.
Yet travelers should remember that air travel involves more than a plane.
As more people start traveling for the holidays, airports will start to get busier.
Experts say it's crucial to wear a mask while walking into an airport, going through security, boarding the plane, sitting through the flight and arriving at the destination.
The study has a few more caveats: Researchers only used a surgical mask and simulated what would happen if only one sick passenger was on a full plane. It also does not account for eating and drinking, which allows travelers to take off their masks briefly.