Utah has one of the highest vaccination exemption rates in the US. In the state, parents are allowed to cite medical, religious or philosophical objections to immunizations (rather than just medical or religious reasons, as in most other states). In essence, this permits parents to refuse vaccination for their children for any reason they want. As a result, a substantial number of Utahian (?) kids don't get vaccinated- approximately 5% in the Utah County, which is the focus of this article.
This piece provides a thorough look at the arguments of pro- and anti-vaccination advocates. It notes that mandatory vaccination is a unique area of American public policy- a law that citizens can choose not to follow.