Public health policies that drew little attention for decades are now so politically toxic that few lawmakers want to take a recorded vote on the issue. And fewer still feel comfortable talking about updates to the state's vaccination schedule or getting rid of certain vaccine exemptions. Even bills mandating vaccine information for adults are shot down as they wend their way through the legislative process.

As Oklahoma joins 25 other states in the worst measles outbreak in a generation, changing the state's vaccination policies has become the latest third rail of politics. Public health officials appear paralyzed almost to the point of inaction, and many lawmakers beg their colleagues not to sponsor vaccine-related bills that could embolden potential opponents.

Former Sen. Ervin Yen is a cautionary tale in the standoff. Yen, an Oklahoma City cardiac anesthesiologist, lost in last year's Republican primary after speaking out pointedly for change in the state's immunization policies.

Almost a year later, he's hesitant to blame his loss solely on his pro-vaccination bills but said he has no regrets. His comments and legislation on other public health issues also drew the ire of medical marijuana proponents, midwives and nurses.

"Obviously, trying to educate the public like we were trying to do does not work, and the 'anti-vaxxers' are quote, 'educating' the public better than government or medicine," Yen said. "Among legislators, they are afraid of bringing this up because of what happened to me …  I don't think they actually un-elected me, but a lot people think that."

Yen was elected in 2014 and soon introduced bills that limited exemptions for vaccinations needed for school enrollment. They went nowhere in Yen's first session. The next year, he authored bills that would have required parents to get information from a doctor before filing for a vaccine exemption. Those failed too, but his efforts drew the attention of a group of parents who believe their children were harmed by vaccinations.