Autism

This article is a good introduction to what an increasing number of people believe. There is some evidence that a mercury based preservative in some vaccines can cause autism. This preservative was recently removed from all infant vaccines because it was proven harmful, but for some reason it is still used in flu vaccines.

Every parent has to make their own decision about vaccines for their family, but I think it is important to be well-informed about the choice, not just choose it by default.