And lo, it is these very same L.A. neighborhoods that are experiencing a resurgence of diseases like whooping cough, otherwise known as pertussis. Measles cases have also hit a high in California this year.

To be clear, not all PBEs are evidence of an anti-vaxxer parent. Schools require either a PBE or an up-to-date shot record for school attendance, and sometimes parents submit them if they simply aren't able to get the shots done on time. Still, the L.A. Times has previously reported that the percentage of kindergartens in which at least 8 percent of students were not fully vaccinated because of the parent's beliefs had more than doubled since 2007, and private-school parents were likelier to file the PBEs than their public-school counterparts. The paper found that the exemption rate for all of Santa Monica and Malibu was 15 percent.

The Hollywood Reporter interviewed several Westside doctors who seem to encourage this kind of vaccine roulette, as well as several area school administrators who seem only vaguely aware of the risk.

“I’d prefer that children be immunized," Shari Latta, director of Children’s Creative Workshop in Malibu, told THR. "We’ve been fortunate to avoid any outbreaks.”

So fortunate! If only there were something parents could do to improve those fortunes ... a way to, say, inoculate their families against the tragedy of untreatable disease.

The anti-vaxxer turn is a frustrating development for a city that's obsessed with health and fitness. There are very few things that we know prevent sickness without a doubt. The "Beaming" juice at L.A.'s Cafe Gratitude, which consists of carrot juice, camu-camu, and astralagus, and which is surely delicious and beam-inducing, is not one. Vaccines are.

It's tempting to suggest, as some of Baum's L.A. sources do, that these are just concerned, well-meaning parents who, along with forbidding processed food and dragging their offspring to baby yoga, also avoid any medications that aren't strictly "natural." (Of course, vaccines are natural—they're derived from the naturally-occurring pathogen itself.)

That kind of thinking ignores the way vaccines work, through herd immunity. A community can only be protected when 92 percent or more of a population is immunized, and many of L.A.'s elementary schools are dipping far below that number. These parents aren't just risking their own kids' health, they're risking everyone's.

Wealth enables these people to hire fringe pediatricians who will coddle their irrational beliefs. But it doesn't entitle them to threaten an entire city's children with terrifying, 19th-century diseases for no reason.