Much has been spoken about how the air inside of airplanes could make passengers sick, but, compared to the germs that can collect on a person’s hands in travel, that which is inhaled is minimal. The air on planes is a half and half mixture of fresh outside air and recycled air from the cabin, though all of the air that goes through the system is sent through a filtration system.
So the only chances of catching air born pathogens on plane is restricted to your immediate area, before the air can be filtered. It is untrue that if a passenger sneezes on a plane it is sent through the entire cabin.
As a pilot stated:
“Most people get sick after traveling not because of what they breathe but because of what they touch. Always assume that the tray table and the button to push the seat back have not been wiped down, though we do wipe down the lavatory.” -Air travel insights from pilots
Typically, airplane air – about half from outside and half recycled after being passed through filters – enters at the top of the cabin. From there, the ventilation system keeps it from flowing forward and backward in the plane, limiting it mostly to the immediate row, before exiting through grilles in the cabin floor. –Health on an airplane
“The air is in fact quite healthy, because of the excellent cabin air filters,” said Joe Lundquist, an air filtration expert with Pall Corp. He says state-of-the-art HEPA air filters can capture up to 99.9% of small bacteria and viruses — even SARS and bird flu virus. –Air on planes is healthy
So it is vastly more prudent to worry about the germs on your own hands than some passenger breathing twenty rows ahead.