Winter is more than just Christmas and fun in the snow. It’s also a time with lots of flus, colds, and other infectious diseases. The flu virus, for example, revels in winter, so from November to March it experiences an annual comeback in our hemisphere. And as we all know, there’s always that one co-worker who just won’t take an illness as a reason to lie at home in bed. He heads off to work as a loudly groaning hero and passes his infection on among his teammates. How can you defend yourself?