Topics: Biology, COVID-19, Research
With COVID-19 reaching the most dangerous levels the U.S. has seen since the pandemic began, the country faces a problematic holiday season. Despite the risk, many people are likely to travel using various forms of transportation that will inevitably put them in relatively close contact with others. Many transit companies have established frequent cleaning routines, but evidence suggests that airborne transmission of the novel coronavirus poses a greater danger than surfaces. The virus is thought to be spread primarily by small droplets, called aerosols, that hang in the air and larger droplets that fall to the ground within six feet or so. Although no mode of public transportation is completely safe, there are some concrete ways to reduce risk, whether on an airplane, train or bus—or even in a shared car.
At a casual glance, air travel might seem like the perfect recipe for COVID transmission: it packs dozens of people into a confined space, often for hours at a time. But many planes have excellent high-efficiency particulate air (HEPA) filters that capture more than 99 percent of particles in the air, including microbes as SARS-CoV-2, the coronavirus that causes COVID. When their recirculation systems are operating, most commercial passenger jets bring in outside air in a top-to-bottom direction about 20 to 30 times per hour. This results in a 50–50 mix of outside and recirculated air and reduces the potential for the airborne spread of a respiratory virus. Many airlines now require passengers to wear a mask during flights except for mealtimes, and some are blocking off middle seats to allow more distancing between people. Companies have also implemented rigorous cleaning procedures between flights. So how does this translate into overall risk?
“An airplane cabin is probably one of the most secure conditions you can be in,” says Sebastian Hoehl of the Institute for Medical Virology at Goethe University Frankfurt in Germany, who has co-authored two papers on COVID-19 transmission on specific flights, which were published in JAMA Network Open and the New England Journal of Medicine, respectfully. Still, a handful of case studies have found that limited transmission can take place on board. One such investigation of a 10-hour journey from London to Hanoi starting on March 1 found that 15 people were likely infected with COVID-19 in-flight—and that 12 of them had sat within a couple of rows of a single symptomatic passenger in business class. (The results were published this month in the U.S. Centers for Disease Control and Prevention’s journal Emerging Infectious Diseases.) Most of these flights occurred early on in the pandemic, however, and in the case of the March 1 flight, masks were likely not worn, the researchers wrote. Meanwhile, a recent Department of Defense study modeled the risk of in-flight infection using mannequins exhaling simulated virus particles and found that a person would have to be exposed to an infectious passenger for at least 54 hours to get an infectious dose. This finding assumes the infected passenger is wearing a surgical mask, however, and it does not account for the dangers involved in removing the mask for meals or talking or in moving about on the plane.
Evaluating COVID Risk on Planes, Trains, and Automobiles, Sophie Bushwick, Tanya Lewis, Amanda Montañez, Scientific American