The Economist's Gulliver blog this morning asked exactly the same question I did when I woke up: how likely is it to get ill from flying on an airplane? Not very:
Planes are widely regarded as flying disease-incubators. If one passenger is sick with a contagious disease and coughing those germs into the air, it makes sense for fellow-flyers to feel that the germs will simply be inhaled by everyone else on the flight, since there is nowhere else for the things to go.
In reality, though, the situation is not that bad. Allen Parmet, a former US Air Force flight surgeon who serves as an aerospace medicine consultant, explained recently to The Verge, a technology and science news site, that infections actually don’t spread well on planes. The reason is the very dry air in the cabin. Many bacteria die in the low humidity. As for viruses, they travel on water droplets when a person coughs or sneezes. But these water droplets also evaporate in the low humidity, and the plane’s fast airflow from ceiling to floor prevents them from travelling far.
[M]ost viruses take days to show symptoms, and there were indications that the illness was contracted by people before they boarded the plane. This tale will probably end the usual way. A few passengers, by the laws of probability, will get sick in the coming week, and they will assume it had something to do with all the germs floating around the plane. It may not be true, but it is for them a satisfying enough explanation.
Well, sure, but I swear the dozen or so babies and toddlers running around (literally) my cabin earlier this week may have contributed to how I felt today.