California just made it nearly impossible to refuse vaccines. Why don’t other states?

California just made it nearly impossible to refuse vaccines. Under a new bill, signed into law by Gov. Jerry Brown yesterday, virtually all children will need to be vaccinated if they want to attend school — unless they have a good medical reason for opting out. No longer will parents be able to get their kids to avoid vaccines for religious or philosophical reasons.

So why don’t all states do this?

After all, the rationale for California’s bill was fairly simple: The state had pockets with too many people denying vaccines for personal reasons — a major contributing factor to a measles outbreak that started last year in Anaheim’s Disneyland and turned into one of the largest in recent US history.

Yet California is far from the worst offender on the unvaccinated front. There are indeed clusters of vaccine denialism in the state, but California’s overall exemption rate is 3.3. percent. While that’s higher than the median state exemption rate (1.8 percent), it’s much lower than the percentage of vaccine exemptions in Oregon, Michigan and Vermont. Idaho, Illionois, Maine, Wisconsin, Arizona, and Alaska, among others, also have higher rates of people opting out for non-medial reasons.

This helpful chart from Mother Jones gives a sense of the landscape:

All these opt-outs have helped spur the return of entirely preventable outbreaks and put public health at risk. Ohio, for instance, recently had one of the largest measles scares of the last decade; it originated with a group of Amish who refused vaccines over medical concerns.

Strict laws like the one California just enacted do seem to get around this problem. Consider West Virginia and Mississippi, both of which put in place similar laws back in the 1970s. Despite their relative poverty, these two states boast very high rates of vaccine coverage and haven’t seen a measles outbreak since the early 1990s. It’s possible these laws aren’t the only reason for the popularity of immunizations in these states, as Wired magazine points out, but there does appear to be some correlation between places with more exemptions and higher rates of vaccine refusal.

So far, however, only three states use strict measures to clamp down on vaccine deniers — California, West Virginia, and Mississippi. Other states have tried but failed. Last year, at least 11 state legislatures considered bills related to immunization exemptions. In many cases, the bills were stopped by vocal opposition groups arguing that vaccine mandates are unconstitutional and a violation of the rights of parents to make medical decisions about their kids.

We’ll see if California’s experience emboldens other states. When its bill ending exemptions, SB277, was introduced in February, the governor and the state’s lawmakers also faced tough opposition from loud opponents who waged very elaborate campaigns to turn public opinion against the bill. Their protests involved advertisements in local papers, marches, and even robocalls. The opposition became so fierce, one senator had to shut down his district office over safety concerns, as the Washington Post reported.

After signing the bill, Gov. Brown said science needed to trump politics when it comes to vaccines and public health. Lawmakers may also have also realized that vaccines are actually overwhelmingly popular. In California, coverage rates hover around 90 percent, which isn’t great for herd immunity but it does mean the majority of parents willingly sign up for shots. The opposition in California was coming from a small, albeit vocal, minority. That’s a lesson for other states.