I'm sure everyone is different, but this has served me well for 30 years now.
Since we're talking health, I'll add a tid bit. - I was at the hospital to visit a friend two years ago and stopped by the snack bar in the lobby where I heard three doctors talking about flu shots being given on another floor. One of them seemed negative and I thought I heard him say, "I'll pass". When the other docs left I asked him about the shots which I don't take. I joked and said my take is that if everyone else gets one there will be no one to make me sick. He said the best safeguard against flu is frequent hand washing and advised me to pick up a small bottle of clear iodine, not the red stuff, and apply it around my nostrils several times a day to act as a disinfectant. Although flu is not primarily an airborne virus we touch our faces, especially around the nose a lot.
Thanks!