It's a common assumption that because an aircraft cabin is an enclosed space with recirculated air, passengers will be exposed to cold viruses or other infectious agents expelled by sneezes or coughs from sick passengers. But research suggests the air on a plane is generally not a cause for worry. More important is who sits near you.
Most commercial flights use recirculated air as opposed to fresh air from outside the plane. Fresh air may sound cleaner, but 50 percent or more of recirculated air travels through high-efficiency filters that eliminate 97 to 99 percent of the bacteria, viruses, fungi, and dust. Also, most aircraft circulate air side-to-side in sections of the plane, rather than the length of the cabin, limiting exposure to airborne particles.
A study in the Journal of the American Medical Association found that, on flights from San Francisco to Denver, passengers in airplanes with recirculated air reported no more colds than passengers in planes using fresh air.
However, your proximity to someone with a cold or flu does seem to matter. A review of research in The Lancet concluded that the risk of becoming newly infected on board an airplane is most closely associated with sitting within two rows of an already-infected personduring a flight of eight hours or more.
The overall risk is similar to the risk in other confined spaces such as a bus, train or classroom. Just as in those circumstances, on an airplane you may not always be able to avoid being close to someone who is coughing and sneezing. But good hygiene can help prevent infections.
Most effective: Washing your hands before eating and not touching your nose, eyes or mouth during the flight.
Source: Prepared by the Editors of The Johns Hopkins Medical Letter: Health After 50