Thanks for the link and info. I feel more informed now and I learned something new.
here's another link:
http://www.agingwell.state.ny.us/flu/flureview/caqs1.htm#q01
Most years at least one of the influenza virus subtypes changes. The results of this change are viruses and virus combinations against which previous years' vaccine formulas offer little protection. A government agency monitors the flu to identify and to track the most common virus variations. Based on data collected from previous years and on predictions about which virus strains will be most prominent in the coming year, this agency decides what subtypes of killed virus to include in the current influenza vaccine.
FR is great, ain't it!?