Case has brilliant insights into systems: "Peace is not the mere absence of war; health is not the mere absence of disease; success is not the mere absence of disaster."
I'd like to see a model like that adapted for vaccinations. So you can easily see the risk (for infants/elderly) dramatically increase as vaccination rates decrease a tiny bit.
http://longnow.org/seminars/02017/aug/07/seeing-whole-system...