Myths:
First class passengers don't catch flu
Masks will protect against flu virus
Keeping a hand kerchief or nap[kin to cover the mouth will contain the flu virus
If X number of viruses are leased and Y number of passengers are in the economy class (Y being a higher number), the chances that any one catching the virus is high; however, if X number of virus are released and s (s being a much smaller number) being the number of first class passengers, the number of virus particles per passenger is high.
It takes 3-5 days for the symptom to show up. It is unlikely to catch the virus on the way to airport and show symptoms in the flight. Likewise, you cant blame the passenger for spreading cold if you get exposed to others during the 3 to 5 day incubation period.
Sneezing/coughing could travel up to 20 feet. It can travel up to 200 miles per hour. So, you could catch a cold even from the economy class.