Airplane air is reportedly changed every 90 seconds, so for a 30' diameter wide body, air is moving about 1' every 3 seconds.
That is not reassuring as one squeezes past the guy in the middle seat on the way to the window seat. One will be well within the middle seat person's breath radius long before any air change has taken place.
I don't think the airlines understand the problem, judging by their public reactions to date.