I don't plan on getting one. I know exactly what makes me ill (lack of sleep), I can usually spot it cominga few days off and I can normally just sleep it off. Outside of the normal cold, I just don't get ill. My bodies immune system can handle pretty much anything on it's own, and I don't like the thought of having any more needles stuck in me than neccessary, particularly for something that 99% of the time I know I won't ever need anyway.