There's a world of difference between a heavy slugger like polio, and a seasonal flue. I'd be happy to get a cholera shot (again) in the face of an epidemic, or even to prevent one. But I have never had a flu shot I can recall, and have never had a serious bout of flue. I trust my immune system for the general run of things (so too speak) more than I trust large pharmaceutical companies, as a general rule.

A