Decades after vaccines effectively wiped out serious diseases such as polio, measles and mumps in the United States, immunization—particularly for children—continues to be debated and even avoided. A notable minority of parents don’t keep up with their children’s vaccine schedule or forego immunization, citing concerns about vaccine safety, a link to autism (despite the lack of any definitive evidence), “too many” vaccines in the early childhood years, or their child’s distress at receiving an injection.