An outbreak of measles, which is causing a full-blown public health emergency in the Pacific Northwest, is a wake-up call to states like Massachusetts that have seen a worrying rise in vaccine rejection. The Commonwealth’s numbers are headed in the wrong direction, and it shouldn’t take a crisis here to tighten the rules that have allowed too many parents in Massachusetts to skip shots for their kids and thereby endanger the entire community.

Washington State has reported 50 confirmed cases, and roughly 30 more have been recorded in nine other states since the start of the year. Measles is a serious, highly contagious disease that can cause brain damage and, in about 1 in 1,000 cases, death.

Massachusetts doesn’t have such a loophole, thankfully — though as recently as 2015 the Legislature had to beat back a misguided attempt by state Senator Joan Lovely to create one. And statewide it has a 95 percent vaccination rate — one of the nation’s highest.

But the Commonwealth does allow religious exemptions, and the number of parents who have claimed them has skyrocketed. In the 1987-88 school year, only about 0.18 percent of children in Massachusetts were unvaccinated for religious reasons. Last year, that figure had climbed to 1.08 percent.

And the statewide number masks some alarming clusters of vaccine rejection. For instance, the Hartsbrook School in Hadley reported a 25 percent exemption rate for the 2017 school year. The Highland School in Westfield and the West Tisbury School on Martha’s Vineyard reported a 20 percent exemption rate. The state doesn’t break down types of exemption at the school level, but statewide, over three-quarters of all exemptions are religious, according to public health officials.

Exemption rates that high are ominous because they threaten herd immunity — the community’s collective resistance to contagious disease — which is needed to protect the small number of children who can’t get shots for legitimate medical reasons. Parents who refuse to vaccinate kids aren’t just putting their own children in danger; they’re putting the vulnerable population that relies on herd immunity at deadly risk.

The spike in religious exemptions — unconnected to any known shift in the state’s religious demographics — coupled with its particular geographic distribution raises the possibility that parents in the state’s crunchier precincts are just labeling their philosophical objections “religious” to get around the law.

There’s little to stop them from doing so. Currently, the immunization law is so vague that the only thing a parent has to do to claim a religious exemption is to sign a form stating they have a sincere religious belief that doesn’t let them vaccinate their children. No interview, letter from a priest, or further documentation is needed.

Another factor that should raise skepticism about the rise in religious exemptions is that no major religion has a formal stance opposing vaccination based on theological doctrine. Indeed, research in the journal Vaccine found that, in many cases, “ostensibly religious reasons to decline immunization actually reflected concerns about vaccine safety or personal beliefs among a social network of people organized around a faith community, rather than theologically based objections per se.”

Dr. Amy Tuteur, a Boston-based blogger and author who often writes about vaccine rejectionism, is more blunt when describing the ideological nature of the parenting trend driving the increase in exemption rates. “The movement is not about vaccines and it’s not about children,” she said. “It’s about parents and how they want to view themselves.” These parents are free-riders, Tuteur said. “They’re willing to receive the benefit of vaccination — the lack of disease — but not willing to contribute to upholding it.”

Other sociologists have found that parents who opt out of vaccination are more likely to favor organic and natural foods, and are motivated primarily by strong-held values of liberty and purity. This may explain why the standard messaging around vaccine education, which emphasizes public health, doesn’t break through.

Or if, as seems likely, parents are blurring the line between personal and “religious” objections, the state could just make them much more laborious to claim. How about making parents show up for an in-person interview with health officials or religious experts to assess the validity and sincerity of their claim?