A recent study in the Elsevier publication, Travel Medicine and Infectious Diseases, suggests that one passenger contracted COVID-19 from other passengers because his mask was worn incorrectly and not at all times.

On the flight from Singapore to Hangzhou in China, which took place during the early stages of the coronavirus outbreak in January, 16 passengers among the 335 aboard were subsequently diagnosed with COVID-19. However, unlike the other infected passengers who are likely to have caught the virus in Wuhan, China, one passenger apparently caught the virus from a fellow passenger, even though he wore a mask for most of the time he was in flight.

The study, which has just been released, found that this passenger most likely caught the virus because he was seated in a row with infected passengers and admittedly wore his mask below his nose for a significant part of the hour-long journey.

The study, which traced all 335 passengers, found the other 16 individuals who were symptomatic at the time of flight may have contracted COVID-19 in Wuhan. The results suggest that only one passenger on a full flight was found to have caught the virus from onboard transmission, and the passenger admitted he did not use his mask as recommended.

However the findings underscore the need for masks as a first-line level of defense against the spread of the virus.

Airlines and aircraft manufacturers point to the fact that state of the art HEPA filters on modern airliners catch and remove viral particles from circulated air. However, the aviation industry also supports the correct use of masks and some social distancing to make a difference for travel health safety, both in-flight and at airports.

American Airlines, Delta, United and Southwest all followed an Airlines for America requirement issued last month making mask wearing mandatory. American closed loopholes, including medical exemptions, for anyone over the age of 2. Delta is allowing passengers with medical exemptions to use the airline’s physician service to verify those claims prior to boarding. United stated that those with extenuating circumstances must contact the airline before traveling without a mask.

The question of masks on flights has become something of a political issue as well. To date, the TSA has deflected calls for the government to issue mask mandate for airline passengers, deferring judgement on the issue to airlines themselves, prompting criticism from Democrats.

“Wearing masks, like requiring seat belts or banning smoking, is absolutely fundamental to protecting passengers and crew during these unprecedented times,” said Sen. Richard Blumenthal, a Connecticut Democrat, in a response to the study.