One of the theories as to why seasonal flu is seasonal has to do with indoor humidity. In the summer, indoor humidity is normally high. Expelled droplets settle to the floor or other surfaces. People touch surfaces, but luckily they don't breathe them.
In the winter, indoor humidity is generally low. Droplets tend to dry out before they reach the floor, leaving the virus itself to float in the air for a prolonged period.
Of course, it's always winter at 38,000 feet. That may make recirc fans and HEPA filtration even more important. On the other hand, increasing the frequency of air changes could lower the humidity even further, and perhaps make things worse.