I would opine there are many things we do that are common sense that won't "prevent" disease or infection, but MIGHT reduce the chances.

Masks do not PREVENT covid infection, but can reduce probability of getting it.
washing your hands and avoid touching your nose eyes, mouth will not prevent seasonal flu but.....
Gargling with antiseptic mouthwash will not PREVENT infection but might reduce the chance (and wont increase it)
pissing and washing your cock after raw fucking wont prevent infection, but might reduce the chance.....
Shitting the cum out of your ass and douching after receptive anal sex..... who knows.. but I do it anyway to avoid wet underwear.