Flying During Pandemic Is Low-Risk, Harvard Researchers Say

Air travel during the pandemic is no more risky than going to a grocery store, says a Harvard University report out this week.

Researchers found “a relatively very low risk of acquiring SARS-CoV-2 [COVID-19] while flying” thanks to plane air-filtering systems and requirements that passengers wear masks.

Researchers from Harvard T.H. Chan School of Public Health explained that powerful HEPA (high-efficiency particulate air filters) systems on planes that change the cabin air 20 to 30 times an hour, coupled with passengers’ consistent compliance with mask rules make air travel an unlikely source of infection. And, they said the low-risk of infection applies no matter where you sit. “We didn’t see any meaningful difference at all” in the potential risk of sitting in a window, middle or aisle seat, said Jack McCarthy, an environmental health-risk expert and president of the consulting firm Environmental Health & Engineering, who was part of the Harvard research team.

The report is based on a study of virus particle flow in airplanes that was funded by the airline industry’s Aviation Public Health Initiative. The researchers stressed that their analysis of the results is nonetheless impartial, and it confirms similar conclusions reached by a recent Department of Defense study that found that the odds of the tiny virus droplets expelled by an infected passenger reaching the “breathing zone” of another passenger are only 3 in 1,000 — if both are wearing masks.

Risk is likely no longer low, however, if “someone does something really obnoxious, like takes off their mask and coughs on you,” said John Spengler, an environmental health professor at Harvard’s Chan School.

McCarthy noted that passengers should minimize the time they take off their masks for eating and drinking: Don’t “take 45 minutes to drink a cup of coffee,” he said. And the report suggests that “when one passenger briefly removes a mask to eat or drink, other passengers in close proximity should keep their masks on.”

 Airlines now refuse to carry passengers who won’t wear masks; Delta recently revealed that it had added the names of 460 noncompliant passengers to its no-fly list, and the industry has urged the federal government to mandate that face coverings be worn in-flight. Airlines including Delta, United and American have gone further, requiring passengers to wear masks at check-in and throughout the areas the airlines manage in the airport, including baggage claim. (While the TSA requires its workers to wear masks during screening, it only encourages travelers to do so.)

And the high-tech HEPA filters used by all the major airlines are thought to contribute significantly to eliminating viral spread. They can remove at least 99.97 percent of dust, pollen, mold, bacteria and airborne particles that are 0.3 microns in size, according to the Environmental Protection Agency. The CDC concurs on their efficacy: “Most viruses and other germs do not spread easily on flights because of how air circulates and is filtered on airplanes,” it notes in its guidance for travel during the pandemic.

The report suggests that airlines also continue with their vigorous cleaning protocols and social distancing measures, such as trying to prevent passengers from bunching up on the jet bridge while waiting to board.

Safety, of course, is an issue that’s at the top of mind for many Americans now considering their holiday plans — just as air travel is beginning a bit of a rebound: On Oct. 18 more than 1 million passengers passed through TSA checkpoints for the first time since the pandemic began its surge last spring. But that’s still down from 2.6 million on the same day in 2019.

Travelers can find some assurance in the fact that the CDC has yet to confirm any cases of COVID-19 transmission on U.S. flights, although the agency did find evidence that “strongly suggest(s) in-flight transmission of SARS-CoV-2” on a 15-hour Boston-to-Hong Kong flight in March. Two passengers on that flight are likely to have transmitted the virus to flight attendants, according to a study in the November 2020 edition of the journal Emerging Infectious Diseases (EID). In another EID study, 16 passengers on a 10-hour flight were likely infected by one symptomatic passenger. Long flights, the study concluded, could potentially “cause COVID-19 clusters of substantial size, even in business class-like settings with spacious seating arrangements.”

“We say in our study, ‘low risk,’ not ‘no risk.’ “ said Leonard Marcus, a leading public health expert and founding codirector of Harvard’s National Preparedness Leadership Initiative (NPLI). “There is always some element of risk … until we have a vaccine.”

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