THey can install better air handllng systems that kill particulate viruses as air gets recirculated. For years, most of our sales force would always get sick after business travel.  I did not- sales mgr asked me how/why-  I gave her a tube of Airborne chewables and said- start taking these a day or two before a trip and one of two things happens- 1: you never get sick, or 2: the duration and symptoms will be greatly reduced if you do get sick.  After a few trips- she proclaimed that it was the best thing since sliced bread!