It's called "onion therapy" and it's older than dirt.
In 1973 it was scientifically proven by a nobel prize winner in medicine that one teaspoon of onion juice was the equivalent to 3 days on antibiotics. So, if you have a nice fat, sweet, onion in your kitchen, take 1/2 of a medium sized onion and drop it into your blender. Get one tsp of fresh onion juice, adminster to anyone with a sore throat and/or flu like symptoms. Be forewarned that when the fresh onion juice comes in contact with the bacterium in your throat it will smart for about 3 seconds, then it's gone. You are actually feeling the death of the bacterium. Two doses 12 hours apart, one tsp each dose usually ends a sore throat/flu in that period of time. You can have nothing to eat or drink for 5 minutes and then you are good to go. Because both colds & flu usually start in the throat, if you take this precaution at the first sign of a sore/scratchy throat you will not get sick.
Because onions mutate at the same time and pace as the bacterium in your environment, you never actually get immune to onion therapy. That leaves the only consideration if you happen to be allergic to onions.
If we can train our children and the general public in this knowledge we can stop colds & flu in it's tracks with what you already have in your kitchen.