US health officials are concerned about a growing trend: Parents who opt out of vaccinating their children as required by public schools. In eight states, more than one in 20 public school kindergarten students aren't getting all of the required vaccines, according to an AP analysis. Over the past five years, the rate of exemptions has risen in more than 25 states, and officials are worried about outbreaks. Measles, for example, has re-emerged in areas with higher exemption rates, according to studies; last year, California saw 2,100 whooping cough cases.
Rules for exemptions vary by state and range from religious and philosophical reasons to medical ones, with some parents concerned that vaccines are too risky, despite several studies showing they are not linked to autism. Vaccination rates are still high overall, but areas with high exemption rates—some as high as 50% in rural northeast Washington—are particularly troubling. Officials warn that because no vaccine is 100% effective, even vaccinated children are at risk if disease breaks out. Scarier still, outside the US, polio and diphtheria have re-emerged. "The same could happen here," warns one expert. (Read more vaccine stories.)