IMO, those colds, flu etc are the action of the immune system working to remove toxins in our bodies. By allowing the immune system to work, the immune system gets stronger. Having an upset stomach or diarrhea, the same thing. It is a purging of toxins from the body. I saw this action first hand in my years as an ER nurse. In that environment staff are exposed to all kinds of "germs." New nurses would get ill frequently in the first year or so, but infrequently once their immune systems got stronger. My own sons would joke if I ever got a rare illness, they would say " If mom got sick, we better watch out we don't get it or we might die " 🤣😅