This actually seems like it might be a legitimate subject of regulation:

“When people come together, germs can come together too,” said Dr. Anne Schuchat, director of the CDC’s National Center for Immunization and Respiratory Diseases.

“There are not that many studies about flu spreading on airplanes and trains, but anytime people are close together, there’s a possibility of germs spreading.”

So it may be unsettling to discover that 51 percent of respondents in a recent online poll by TripAdvisor.com would fly while sick with the flu rather than pay a flight rebooking fee. About 2,300 people took part in the survey.

Frequent fliers say the results are disturbing, but not surprising.

“I do think that’s an unfortunate attitude, because the airplane is like a petri dish in the sky,” said Rene Foss, a flight attendant for 25 years and the spokeswoman for the Association of Flight Attendants.

“[But] people really are resistant to paying any extra fees.”

Only Delta waives rebooking fees for travelers who have a doctor’s note saying they’ve got H1N1 (or, presumably, another serious contagious illness). In an ideal market, informed consumers would prefer not to be exposed to such risks and favor airlines with policies like Delta’s. (The airline might also benefit more immediately, from reduced sick days, but I’d expect flight crew to be disproportionately likely to be vaccinated.)  In the meantime, though, this does seem like a disproportionate cost to drop on a plane full of people for the sake of saving a rebooking fee. At the very least, it seems like they ought to be subject to public pressure to change their practice.