When an airplane from Dubai landed in New York yesterday morning with reports of passengers coughing and vomiting, health officials jumped into action—detaining the plane and screening all 549 passengers and crew members for illness before allowing them to disembark. Although initial reports indicated that 100 or more people had concerning symptoms, it was later announced that only 11 people were sick enough to be hospitalized, and that influenza appeared to be the cause.
The nation breathed a collective sigh of relief to hear that the illness was “just” the flu, and not the deadly Middle East respiratory syndrome (MERS) or another, unknown pathogen. Then again, the flu can be extremely serious as well, and it’s pretty scary to think that people who were apparently healthy when they boarded the plane had such serious symptoms just 14 hours later.
That got us thinking: How big a risk is flying, really, when it comes to picking up infections like the flu—and how quickly can transmission really happen? To find out, we looked at the research and spoke with some experts who study this very thing. Here’s what we learned.
Yes, you can catch the flu from your seatmate
It’s still too soon to tell how exactly, or from whom, the people aboard Emirates Flight 203 caught the flu. But a recent study on influenza transmission aboard an aircraft gives us a few hints as to how it may have happened—and how it probably didn’t.
The study, published in March in the Proceedings of the National Academy of Sciences, involved several experiments to test the likelihood of an infected passenger transmitting an illness like the flu—which is known to spread through respiratory droplets—to other passengers. Researchers found that, for people seated within a seat or two to the side, or within one row forward or backward, the chances of catching a contagious virus were about 80%.
But probably not from someone several rows away
Outside of that immediate radius from a sick passenger, however, the risk was much lower—only about 3%. Because air droplets from sneezing and coughing don’t typically travel much farther than a few feet, most passengers on the plane would be protected from an airborne virus, says Vicki Stover Hertzberg, PhD, professor of biostatistics and bioinformatics at Emory University and first author of the study.
Hertzberg says it’s a myth that recirculated air in planes make it more likely for viruses to spread through an entire cabin. “Most modern planes infuse fresh air at a very high rate,” she says, “actually more often than in your typical modern office building.”
One other factor to think about, however, is the flight attendants who are constantly moving around the cabin and touching food and beverages. Sick crew members are less likely to come to work than healthy ones, Hertzberg and her colleagues point out in their paper—but if they do, according to the study’s calculations, they’re likely to infect 4.6 people per flight.
Longer flights mean higher risk
There are some other caveats to Hertzberg’s study, as well. The research only took into account the risk due to airborne viruses—not viruses left on surfaces, like a seat back or the bathroom door handle, that could be contaminated by a sick person and then by an uninfected person.
The study calculated risk based on four to five hours in an airplane, with no air circulation whatsoever, to simulate sitting on a tarmac for a long period of time. Then the researchers quadrupled that rate of infection, to assume an “extraordinarily high infection rate” in a “worst-case scenario.”
But Hertzberg acknowledges that the longer the flight, the higher the risk of transmission becomes. “We really didn’t look at long-haul flights, but I will say that the longer you’re in the air, the more people are moving around: using the bathroom, stretching their legs, eating meals,” she says. “So the differential between those people seated immediately around you and those that are not too close to you will start to narrow—not by much, but certainly by a little bit.”
How quickly do flu symptoms appear?
According to the U.S. Centers for Disease Control and Prevention (CDC), flu symptoms “can begin about two days (but can range from one to four days) after the virus enters the body.” So while it’s possible that people caught the flu on board the 14-hour flight from Dubai to New York, it’s more likely that they were already sick when they boarded the plane.
“The flu virus does mutate every year, and it may be that this is some new, fast-spreading strain of influenza—but I doubt that’s the case,” says Ian Sheffer, MD, assistant professor of medicine and infectious disease doctor at Drexel College of Medicine. “I think these folks probably picked it up before they got on this plane, maybe on a previous flight or elsewhere in their travels.”
Airplanes aren’t the only places with germs, after all; airports, hotels, and tour busses can also be full of them. (The trays that hold your belongings in the security line, for example, are a known hot spot for viruses.) And because there’s no routine screening to test people for illnesses before a flight, Hertzberg points out, there’s no way of knowing if these passengers were already infected before they boarded.
What about other illnesses?
Influenza is particularly concerning when it comes to transmission in enclosed spaces because it spreads through respiratory droplets. But it’s not the only illness that spreads that way; MERS, measles, tuberculosis, and severe acute respiratory syndrome (SARS) all operate in a similar manner, says Hertzberg. “The longer you’re in proximity to someone with one of these, the more likely it is you’ll get infected,” she adds.
Norovirus, also known as the stomach flu, can also be transmitted on airplanes, according to previous research. In 2008, for example, more than 20 passengers became sick with diarrhea and vomiting within three hours of taking off from Boston on a flight bound for Los Angeles; in an analysis later published in Clinical Infectious Diseases, researchers concluded that “despite the short duration, transmission of norovirus likely occurred during the flight.”
Of course, plenty of other illnesses can be spread through contact with infected people, too. And even if their airplane transmission rates haven’t been studied, they can still be cause for alarm. In fact, on the same day the Emirates flight was detained in New York City, another airplane was evacuated in France for fear that someone on board might have cholera. (Cholera, which was later ruled out, is a bacterial infection that spreads when the feces of an infected person contaminates food or water.)
And while it’s not technically an illness, there have also been recent reports of bed bugs infesting international flights and biting passengers aboard. Air India, the airline named by several passengers in complaints from earlier this summer, told NBC News that it was “deeply concerned” by the reports—and that it had fumigated and overhauled the upholstery on the planes in question—but called the episodes “isolated incidents.”
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How travelers can protect themselves
Aside from traveling in a literal bubble, there’s no foolproof way to prevent infection from every disease or parasite that’s out there. But Hertzberg says airline travelers can still reduce their risk of getting sick by following a few simple steps.
“What I advise is getting a window seat and staying put,” she says. “The less you move around, and the less contact you have with other people, the lower your chances of picking up an infection.”
Of course, she adds, there’s more to choosing a seat than illness prevention—and some people may prioritize the ability to move around mid-flight over the small amount of protection a window seat provides. People who are at risk for blood clots, like smokers and women taking oral contraceptives, should take special care to get up and stretch their legs during long flights, says Dr. Sheffer.
Being conscious not to touch your face, and to wash your hands after touching communal surfaces, can reduce your risk of infection, as well. Hertzberg also recommends keeping the fan above your seat turned off—not because the air coming through the plane’s ventilation contains flu germs, but because any germs that your seatmate is coughing or sneezing up can get “caught up in that airstream and directed toward you,” she says.
If you’re already sick, on the other hand, and you can’t avoid getting on a plane, you can help reduce the risk of infecting your fellow flyers by keeping your fan turned on. “That way, any germs that you’re expelling will be directed back down toward you and will be less likely to travel to the neighboring seats or rows,” she says.
Dr. Sheffer adds that the best protection against influenza can happen long before people board their next flight. “It’s similar advice to what we’d give anybody during flu season,” he says: “Get your flu vaccine. It’s one of the single best things you can do to protect yourself from picking up influenza, wherever you are.”