Mandatory Vaccinations

Direct exposure is exactly how your immune system builds immunity. So the best way to reduce the problem is to not "fool" the immune system with a vaccine. Vaccines are dead forms of viruses/diseases. However, the immune system only builds a defense against a dead form. If exposed to the living form, the immune system may not be properly prepared for the way the virus/disease acts. Thus causing an infection anyway. Small pox is one example of such occurance, another can be the flu.

Erm, do you know how the immune system works? The body creates anti-bodies for diseases, which connect to the invader and allow them to be caught by white blood cells. but each disease needs a different set of them and they can't make those until the body sees the invader. So even though the virus is dead in many vaccines and doesn't cause any harm, the body can make anti-bodies for the disease and can then fight it before it causes an actual problem. At least, this is my 9th grade bio understanding of it, I'm sure someone else could explain it much more in-depth.