In 2015, California passed a law eliminating personal belief exemptions for vaccinations that kids must receive before they can attend public school. In the years since, there's been a major increase in the number of medical exemptions issued by doctors for these required immunizations, researchers found.
"Experiences With Medical Exemptions After a Change in Vaccine Exemption Policy in California," Salini Mohanty, Alison M. Buttenheim, Caroline M. Joyce, Amanda C. Howa, DanielSalmon, Saad B. Omer Pediatrics Oct 2018, e20181051; DOI: 10.1542/peds.2018-1051