Fisher and other vaccine skeptics say diseases such as measles are bound to pop up, even in communities with high vaccination rates. But public health officials point out that because these diseases are highly contagious, a large segment of the population needs to be vaccinated in order to protect those, like children being treated for cancer, who cannot get immunized for medical reasons.

As the number of unvaccinated children grows, so does the risk of an outbreak, said Dr. Patricia Quinlisk, the state epidemiologist for Iowa. “This is not an individual decision; this is a decision that affects the whole community.”

A growing number of Iowa families are choosing not to vaccinate their children under a religious exemption law. The number of children in kindergarten through 12th grade who skipped vaccinations for religious reasons jumped to 6,737, a 13 percent increase from last school year to this school year.

The exemptions tend to occur in communities where parents share opinions about vaccine safety or hold similar religious beliefs, Quinlisk said, and there’s not much the state can do to challenge parents’ decisions.