The stuff that gets us sick, whether in the air or in foods we eat is always there. Foods can be controlled, eat only warm foods when traveling. Fruits and vegetables can be soaked in water with a few drops of H2O2 (Hydrogen-Peroxid) for ten minutes.
Work on your own immunity. Immunity is built only by nature made raw foods.
Taking CS once a day may not be enough. It may have to be taken twice day in order to have a continuous effect of it.