By Amy Norton
MONDAY, Dec. 18, 2017 (HealthDay News) -- A Washington state law aimed at discouraging nonmedical childhood vaccine exemptions seems to have worked, a new study finds.
The legislation, enacted in 2011, required parents to talk to a doctor before they could get their child exempted from vaccinations for nonmedical reasons.
Researchers found that after the law went into effect, the state's overall vaccine exemption rate fell by 40 percent.
And it remained consistently lower through 2014 -- the most recent year the researchers assessed.
"Not only did the rates go down, but they remained remarkably stable," said lead researcher Dr. Saad Omer, of Emory University's Vaccine Center in Atlanta.
Right now, all U.S. states allow children to skip vaccinations for medical reasons. And 47 states, Omer said, allow exemptions due to families' religious beliefs, "personal beliefs," or both.
Three states allow only medical exemptions. Last year, California became the third, after legislators eliminated the state's nonmedical exemptions.
The move came largely in response to a 2015 measles outbreak that was traced back to California's Disneyland. It ultimately sickened 188 people in 24 states and Washington, D.C., according to the U.S. Centers for Disease Control and Prevention.
The CDC believes it started with a foreign traveler who contracted measles in another country before visiting the amusement park -- where he or she encountered other unvaccinated people.
Health officials put part of the blame on nonmedical exemptions, which have left some U.S. children unprotected against measles and other infections.
According to Omer, Washington state's policy is something other states might want to consider.
"This is a pretty solid option for states to have," he said.
The study, published online Dec. 18 in the journal Pediatrics, couldn't discern why the state policy worked.
But Dr. Paul Offit said he suspects it's because nonmedical exemptions became too much of a hassle for many parents.
"Any policy that makes it harder to get these exemptions, that tests your resolve, would probably have this effect," said Offit, director of the Vaccine Education Center at Children's Hospital of Philadelphia.
He said the Washington state policy may be the "fairest way" to address the issue of nonmedical exemptions: It doesn't take the option away from parents, and instead gets them into a discussion with a health professional.
"But I do think it's best to do what California did," added Offit, who was not involved with the study. "It makes the most sense."
Omer agreed that the Washington state policy probably worked -- in part -- by making nonmedical exemptions inconvenient. But he also suspected some parents changed their minds after talking to their pediatrician.
"For those parents who are 'vaccine-hesitant,'" Omer said, "this [policy] is about providing a fact-based discussion with your provider. Your choice about vaccination is not being taken away."