A study of exemption rates by the Associated Press finds that more and more parents are skipping required vaccines for their children, often out of fear that shots do more harm than good. More than half of all states have seen an increase in the number of exemptions and in eight states, mostly in the Northwest and Midwest, the percentage of kids not getting the full recommendation of shots is over 5 percent.

Doctors cite many reasons for the rise in requested exemptions, one of which is that it is simply easier than it used to be to opt out. In many places, parents who wish to enroll their kids in kindergarten without the required shots simply need to check a box on a form (which can be easier than taking their kids to the doctor.) Other cite religious reasons or the sheer volume of shots, which has increased with the development of new vaccines, like the one for chickenpox.

One of the biggest concerns remains the fear that vaccines cause autism or other development disorders despite the fact that any link between the two has been debunked. Last year, the venerable medical journal The Lancet issued a retraction of a disputed vaccine-autism study that helped launch and promote the fear that the two were related. However, once such a belief is out there, it's nearly impossible to completely refute. The fact that one of the dissenters quoted in the AP story is a nurse (whose husband is an anesthesiologist) shows just how difficult it is to change minds, even in the face (or lack) of medical evidence.

While vaccination rates are still high for most of the country, the larger problem is that exemptions tend to be clustered in certain communities  For example, Washington's overall rate is six percent, but in some rural counties the rate is well over 20 percent, driving up the risk of an outbreak for an otherwise beaten disease. Once an outbreak happens, even kids who received shots are vulnerable since vaccines require a "herd immunity" to be totally effective. Outbreaks of diphtheria, meningitis, and even polio have all affected areas where vaccination rates decline.