when someone sneezes, i exit the situation immediately because i do not want to inhale what they sneezed out and catch what they have (in case it is not a simple nasal irritation due to something in the air).
today i was in an elevator, and someone else in the elevator sneezed, and i instantly seized my breathing mechanism, and i did not inhale until i got out of the lift and i was about 10 meters from the elevator. it was unfortunate that they sneezed at the point where i was fully exhaled, so i did not have any air in my lungs at the point i stopped breathing. as well as this, i ran to get into the lift, so i needed to breathe to recover the oxygen expenditure. i had to travel 4 floors before the doors opened, and i pushed my way out and trotted swiftly to where i again resumed breathing.
to say "bless you" is redundant because it uses up vital air that i could retain until i am out of the danger zone, and it is redundant because it is very unlikely that they had contracted the plague. even if they had contracted bubonic plague or whatever other fatal influenzas of the past that beset people, in todays world, it is unlikely that their sneeze would be an indication of impending fatality.