I find prevention via cellular hydration to prevent cold/flu viruses works best for me. Doses of glutamine, leucine, glycine, and alanine (15g, 15g, 3g, 2g - respectively) mixed in one liter of water consumed every other day or so completely prevents me from catching a cold even when traveling on planes or exposed to others with colds. Has worked for several years (9 and counting).
We used to call this the Swell drink and it is perfect to sip on during workouts...