Good material. Just a quick question regarding viruses that mutate. Why does the "flu" have the ability to mutate so easily from year to year, but other viruses that have affected the public, and killed as much haven't. ie; Chicken Pox and Measles, polio. Why were we able to irradicate these viruses in a short period of time relative to the common flu. Why haven't these other viruses been able to mutate as easily as the common flue to sustain their existence?