Differences in state laws regarding vaccine exemptions makes it easier for parents to opt out of vaccinations for their children in some states, in turn raising the possibility for outbreaks of vaccine-preventable diseases. For example, there were 17 outbreaks and 222 cases of measles in 2011, occurring mostly among unvaccinated people, according to a 2012 report by the Centers for Disease Control and Prevention. Currently, the U.S. is experiencing the largest measles outbreak since 2000, with 592 cases reported in 21 states between Jan. 1 and Aug. 29.
The CDC uses annual reports from state and local health departments to monitor compliance with school immunization requirements to determine total exemption rates across the United States. Exemption can be granted for medical reasons as well as religious and philosophical beliefs. The CDC found that statewide levels of vaccination coverage have reached or are near target levels, but vaccination coverage for extremely transmissible diseases at the local level remains low, such as the measles.
According to the CDC's findings, the following 10 states have the highest rates of children enrolled in kindergarten with a reported exemption to vaccination in the 2011-2012 school year.
1. California — 13,536 total exemptions
2. Illinois — 9,015
3. Michigan — 6,932
4. Texas — 5,947
5. Florida — 3,495
6. Washington — 3,472
7. Arizona — 3,187
8. Oregon — 2,728
9. Pennsylvania — 2,681
10. Utah — 2,032