[inglor_cz]

" you are giving no actionable thing for people to do"

As far as an actionable thing goes, my N == 1 experience says that regular nasal rinsing reduces both frequency and severity of various common colds a lot.

I used to be down with sore throat, running nose and light to moderate cough some 5-6 times a year, since I was a kid until my early 40s. Once I started with the flushing, it all went away. Nowadays, about twice a year I "catch" something, which means a single night of chills and sweating, and in the morning I am fine again. The mucous membranes seem to be no longer susceptible. No sore throat ever etc.

[taeric]

I'm not clear that that is in the same vein as what the parent post meant?

That said, this is an interesting suggestion to follow my post. It literally only works if you have access to clean, probably distilled, water supply. If you don't, you are also introducing a path for some serious problems into your sinuses in the form of parasites.

[inglor_cz]

"access to clean, probably distilled, water supply"

A good antibacterial filter + boiling that filtered water just to be sure goes a long way. That equipment is nontrivial, but for someone in a developed economy, usually affordable. Probably cheaper than being sick often, because even European welfare states often won't give you anything for first days of sickness.

[taeric]

The good filter is again largely to my point. :D

You are correct that boiling it can probably help a lot. You then have to store it in a clean spot for it to cool to a temperature you can use, of course. Something that probably relies more on modern technology than makes sense.