Joseph Allen is assistant professor of exposure assessment science at Harvard T.H. Chan School of Public Health and co-author of the book “Healthy Buildings.”
Before we go any further, let’s make one thing clear: Airplanes are certainly vectors of disease, efficiently transporting infectious people around countries and the globe. This is obviously critical in terms of outbreak control for covid-19. But the fact that airplanes help spread disease across geographies does not mean that you are necessarily at risk during flight. There are fairly simple things you can do, if you do need to travel, to reduce the odds of getting sick.
Billions of people travel by plane every year, yet there have only been a handful of documented disease outbreaks attributable to airplanes in the past 40 years. If planes made you sick, we would expect to see millions of people sick every year attributable to flights. We haven’t seen it because it’s just not happening.
Consider one study that examined a passenger with tuberculosis on an airplane. It found that the median risk of infection to the other 169 passengers on the airplane was between 1 in 10,000 to 1 in a million. Wearing a mask, as some airlines now require, reduced the incidence of infection another 10-fold.
There’s a reason the risks are low. The required aircraft systems do a really good job of controlling airborne bacteria and viruses.
To get technical, airplanes deliver 10 to 12 air changes per hour. In a hospital isolation room, the minimum target is six air changes per hour for existing facilities and 12 air changes per hour for new. Airplanes also use the same air filter — a HEPA filter — recommended by the CDC for isolation rooms with recirculated air. Such filters capture 99.97 percent of airborne particles.
What’s more, airplanes are essentially designed to isolate airflow. Even if someone coughs on your flight without a mask, it is likely those virus particles will travel one or two rows, as evidence from the few outbreaks attributed to the airplane cabin shows.
Still, you might say, this only accounts for airborne transmission of covid-19. To guard against transmission via large droplets and contaminated surfaces, we do need to take some additional steps. Wearing a mask on planes should be mandated, and wiping down tables and arm rests with a disinfectant provides an additional layer of defense.
By this point, you may be thinking, “But I know I get sick when I travel. This article goes against everything I have experienced firsthand.” The reality is that you are more at risk of getting sick when traveling, but it’s not the airplane that’s making you sick.
Every time you fly, you may also take a cab, bus or subway; stand in long lines in the airport; eat unhealthy foods; sit for extended durations; spend time in spaces with hundreds or thousands of other travelers; stay at a hotel or friend’s home; arrive in a different climate and change time zones, disrupting your sleep. All of these factors are known to affect your immune system.
To be clear, I’m not suggesting we go about air travel as we did before covid-19. I’m just putting the risks of time spent on an airplane in context. It is prudent to take additional precautions during a pandemic. In 2013, I was one of the lead authors of a report for the Transportation Research Board of the National Academies on infectious disease mitigation in airports and airplanes. Let me distill some of the recommendations from that report to those that are most applicable now and add a few new ones based on what we now know about covid-19.
For starters, airports should mandate mask wearing; increase ventilation rates; make bathrooms touchless; consider deploying upper-room germicidal UV fixtures in areas with high-occupant density; institute temperature screening; deploy hand-sanitizer stations; and, once passengers arrive at their gates, require that they stay in their designated area except for bathroom usage.
Airlines should ensure gate-based ventilation is operating during boarding and disembarkation; carefully choreograph the loading of airplanes; mandate mask use; and provide meals and bottled water during boarding and discontinue in-flight meal and drink service.
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Individuals have an important role to play, too. First, stay home and do not travel if sick. Comply with rules for mask wearing; wash hands before and after each step at the airport; keep the personal overhead ventilation on and pointed down; and maintain physical distancing to the extent possible.
If the necessary precautions are taken, and people do their part and behave according to rules, there is a path back to air travel. But we should all consider this a privilege — one that can be revoked quickly if conditions change or if crowds do not act appropriately.
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