In 2015 there was a measles outbreak in Southern California, which I remember vividly because I had an infant at the time. The state responded by eliminating personal belief exemptions for vaccines.
Have things improved since then? My gut tells me no, since increased government efforts can be easily overwhelmed by a concerted anti-vaccination push. But CDC data shows that from 2011 to 2023, California exemption rates dropped by 2.5 percentage points (2.6% to 0.1%) while MMR vaccination rates for kindergarteners increased by 3 percentage points (93% to 96%). Meanwhile, in my birth state of Idaho, exemption rates increased by 9 percentage points (5% to 14%) and MMR vaccination rates decreased by 9 percentage points (89% to 80%).