AP IMPACT: Fears of disease outbreak? Half of states see rise in kids skipping school shots
Health officials have not identified an exemption threshold that would likely lead to outbreaks. But they worry when some states have exemption rates climbing beyond 5 percent. The average state exemption rate has been estimated at less than half that.
Even more troubling are pockets in some states where exemption rates are much higher. In some rural counties in northeast Washington, for example, vaccination exemption rates in recent years have been above 20 percent and even as high as 50 percent.
“Vaccine refusers tend to cluster,” said Saad Omer, an Emory University epidemiologist who has done extensive research on the issue.
Parents who let their kids skip some vaccines put others at risk, health officials say. Because no vaccine is completely effective, if an outbreak begins in an unvaccinated group of children, a vaccinated child may still be at some risk of getting sick.
I didn't include the whole article, so here is the link if you want to read it: http://www.washingtonpost.com/national/health-science/ap-impact-fears-of-disease-outbreak-half-of-states-see-rise-in-kids-skipping-school-shots/2011/11/28/gIQAX2Zv5N_story.html 
Do you think it's fair for non-vaxers to put other children at risk for their choices?