Somewhere in Orange County, Mary Poppins may be running a fever. The same could be true for her coworkers—an unsuspecting Ariel, say; a suddenly swoony Goofy or Pluto or any of the other 23,000 people (OK, or characters) who punch in for work at Disneyland every day. And the same could be true too for any one of the estimated 16 million people who will pour into the theme park this year.
The reason? Measles. The cause? This may not come entirely as a surprise: the anti-vaccine crowd.
Just when you think they’ve been run to ground, shamed into silence, and just when you can watch a whole evening of Jenny McCarthy co-hosting the New Year’s Eve celebration in Times Square and not hear her utter a word of unscientific nonsense, the anti-vaxxers come roaring back. Less than two weeks into 2015 come the year’s first stories about the latest victims of the nation’s declining vaccine rate. And this time, ground zero is the self-proclaimed Happiest Place on Earth, which is in danger of becoming the decidedly less consumer-friendly Most Expensive Disease Vector on Earth.
The epidemiological numbers seem small, but the implications are big: from Dec. 15 to Dec. 20, at least 20 people are reported to have entered Disneyland’s gates healthy and exited with measles. Of those victims, 15 were unvaccinated. Those infections occurred in a year in which California as a whole had its highest measles caseload in two decades—66, with 23 of them in Orange County. The U.S. recorded 610 cases total in 2014, triple the number as recently as 2011.
It’s no coincidence, as TIME has reported, that the areas of the country with the highest vaccine refusal rates—Orange County; New York City; Columbus, Ohio; Silicon Valley—have higher rates of outbreaks of vaccine-preventable diseases, too. What gives the anti-vaccinators so much power to do so much harm is that once vaccine rates fall below 95%, herd immunity—the protection that a well-vaccinated community offers to the few people in its midst who must remain unvaccinated for legitimate medical reasons—starts to break down. In 2012, California was right at that baseline 95% vaccination rate for measles and whooping cough. It’s now at 92%.
Those small percentages can make huge differences. In 2003, a few provinces in northern Nigeria banned polio vaccines, when local religious leaders claimed the drops were designed to sterilize Muslim girls and transmit AIDS. Within three years, 20 previously polio-free countries recorded cases of the disease—all of them the Nigerian strain.
American anti-vaxxers seem impervious to this and other warning flags, like the ongoing whooping cough epidemic in California or last year’s outbreaks of measles in New York and mumps in Columbus. As the Disneyland outbreak is reported here and here and here and here, the reaction is likely to be more of the same—which is to say denial coupled with a lot of echo-chamber prattle about a bought-off media carrying water for big pharma, plus the usual scattering of glib Twitter code like #CDCWhistleblower, which purports to be final proof of the great vaccine coverup, but which is nothing of the kind.
Hashtag science is not real science, and conspiracy theories have nothing to do with facts. The problem is, children infected with measles—or polio or whooping cough or mumps—are indeed very real. In the age of vaccines, there ought to be no place they feel unsafe—least of all Disneyland.
Jeffrey Kluger is Editor at Large for TIME.