If you want to prevent airborne spread of diseases you have a few options:

• Filter breath (masks, PAPRs)
• Replace the air (ventilation)
• Clean the air (filters, UV light)

Masks, fans, and air filters are widely available, but what about UV? The CDC recommends upper-room UV, it has a long history of successful use in with TB, and in many cases it's great fit for the space. Look on Yelp, though, and no installers come up:

Maybe people are missing a good business opportunity, or maybe it's the kind of opportunity that's only ok but is worth it for the altruistic impacts of directly reducing spread and normalizing UV? Seems worth finding out!

If you want to read more about how to set up upper-room UV systems, NIOSH has a serious document. At a high level, though, you want rooms that have a high density of people but also a reasonably high ceiling. Then you set up UV fixtures to shine so they clean the air above the people.

(Prompted in part by thinking that the Cambridge Masonic Hall would be a great place for an installation like this: crowded, tall ceilings, ceiling fans for circulation.)