Shapiro’s Op-Ed provoked such heated discussion among the Times’ readers that the Southern California paper devoted a second item just to the reaction.

Joel Stein wrote in Time magazine a few years ago about his disagreement with his wife over vaccinating their children — he wanted to, she didn’t. Her view was “not unique,” he wrote, “at least not in the liberal, wealthy part of L.A. where we live.”

But it’s not just California. Public health officials see large clusters of unvaccinated children in latte-drinking enclaves everywhere, like Ashland, Ore., and Boulder, Colo., where close to 30 percent of children are exempted from one vaccine or another. In some schools in Ashland two-thirds of the students have exemptions, according to Mark Largent, a James Madison College professor who wrote a book about the vaccine debate last year.

And new data out this month from the Centers for Disease Control shows what Paul Offit, a pediatrician at Children’s Hospital of Philadelphia, calls a disturbing uptick in the number of children forgoing vaccinations. “For the first time ever, there are a handful of states which now have people who are choosing not to get vaccines at the greater than 5 percent level, which is a problem. That’s where you’re going to start to see some of these diseases coming back. And you’re already seeing it with whooping cough and other diseases,” he told Salon. Indeed, the anti-vaccination movement was blamed for helping cause the worst whooping cough epidemic in 70 years.

The states above 5 percent include Michigan, Vermont, Idaho and Oregon. Illinois barely missed the cut at 4.8 percent. The national median is 1.8 percent, with many states below 1 percent, making Vermont (5.7 percent) and Oregon (6.4 percent) more than three times above the national average.

Offit, a prominent skeptic of alternative medicine and pro-vaccination author, explained that high education levels can enhance, rather than deter, anti-vax beliefs. “They’re people who believe that they can know anything and know as much as their doctor — if not more — by simply studying it, reading about it,” he said. Many of these people, he added, are used to being in control of their lives and at their jobs and want to control this aspect of their lives as well.

Science writer Chris Mooney has written that vaccine denialism “largely occupies the political left,” though he later walked that back in light of polling data and pushback from Kevin Drum, David Frum, Andrew Sullivan and others, who pointed out that shopping at Whole Foods does not necessarily make you a liberal. And in Congress, the anti-vax movement is represented by Republicans.

And there’s some evidence to suggest that vaccine denialism is gaining strength on the far-out libertarian fringe of the right, where people like Michele Bachmann, Alex Jones and others have spoken out against what they see as a totalitarian mandate from the government to inoculate your children. That might help explain the presence of Idaho on the CDC list, and the fact that the data show the largest increases in non-medical exemptions came from Georgia and West Virginia.