Winter weather makes most of us apprehensive about getting a cold or the flu, and often enough those fears are justified. No matter how religiously we wash our hands, keep our distance from others who already have the sniffles, or try to fortify our immune system with extra doses of vitamins, it seems to be a losing battle year after year. Yet some folks never appear to get affected. They just sail through this treacherous season without a hitch. How do these lucky few do it?