The science on vaccinations is comprehensive, lengthy, and definitive: vaccinations work, and for decades they have helped U.S. children avoid the crippling diseases that threatened generations before them.

So it is shocking and sad to learn that a record number of California parents are endangering both their children and public health by opting out of vaccinations. The rate of personal-belief exemptions at California kindergartens with 10 or more students has doubled since 2007.