I can tell you my remedies. They work like magic: I have not had any upper or lower respiratory infections for well over a year.

1) Very high consumption of fermented dairy, which contains beneficial bacteria that improve our immune system's defense mechanisms. My fridge may be almost empty at times but it would always contain a bunch of Fage 0% greek yogurt. Chobani is another good brand.

2) Not washing my hands excessively. If I come back home from a grocery store where I touched objects touched by other people, I do not wash my hands. I never ever use hand sanitizer. I welcome germs and viruses and let my immune system practice fighting them.

3) High intake of tea, to always keep my system well flushed.