It's actually impossible.
Really? I happened across this study on air travel and contraction of airborne illnesses like
the common cold and flu; the result were a bit surprising. So ... imagine yourself sitting on a plane filled to near capacity during flu season, you hear a number of folks hacking & sneezing away (or even talking) and you begin to cocoon yourself into protective ball and turn off that overhead blower (you know, the one that blasts cold air onto your face) thinking "oh great, we're in a pressurized tube with recirculated air ... I'm doomed to catch something!" You know it true - we've all been there.
The good news. This study indicated that it all depends of a few things.
1. How diligent sick passengers treat themselves (sneezing into their backside
elbows is huge start).
2. Depends on your proximity to the sick one. If you're more than 1-meter
away (about 3 ft) in either direction, chances are that you're ok (barring #1
happening). This is because, apparently, their infected vapor droplets don't
travel passed this distance - not even through the aircon system.
3. Your due diligence in hand washing and not rubbing your eyes, picking
your nose or touching your mouth is vitality important as well. I also travel
with those disposable disinfecting wipes and begin my clearing process on
the tray table, arm rests and video screen before each flight just in case a
fellow passenger left a present behind for me. I also use that anti-bacterial
gel to give my hands a once over a few times during the flight just for good
4. Seating matters. Folks seated in the middle part of the plane typically come
into contact with the most people - especially those in the aisle seats while
those in the front or back tend to see less traffic (the back with slightly less).
Next is middle, middle - those in the middle of the plane and lucky enough
to seat in the middle of the row. Best seat in the house? The window seat -
even in the middle part of the plane (remember the 1 meter rule?).
5. Breezy. Contrary to popular belief, it is apparently better to open up that
air-blower above your head - if you point it downward and not at your face.
This pushes those nasty droplets away from you.
6. Above and beyond. In addition to the above, I travel with eye-drops to help
moisturize and clean my eyes, saline spray for nasal passage (I spray a few
times during my flight); it helps keep nasal passages moist and clean, and, I
wear a mask that covers my mouth and nose as an extra precaution for
those wandering airborne droplets from a nearby neighbor. by breathing my
own air, I am also able to help moisturize my nasal passage as well - airplane
environments are extremely dry.
Following the above steps aren't foolproof measures to escape sickness, but they'll at least give you a fighting chance! Fly on and see you in the air!