California had also been struggling to maintain herd immunity vaccination rates (just like us). After trying a variety of interventions- and following a measles outbreak associated with Disneyland- the California Assembly passed & Governor Brown signed Senate Bill 277 (in 2015) which abolished personal exemptions in California.
The intervention worked. In the following years, CA had sharp increases in vaccination rates among kindergarteners entering school. During the 2014–2015 school year the statewide kindergarten full-vaccination rate was only 90.4%. After implementing the new law, the kindergarten full-vaccination rate rose to >95% and has stayed there.