A flier educating parents about measles is displayed on a bulletin board at the Tamalpais Pediatrics clinic Feb. 6, 2015, in Greenbrae, Calif. (Eric Risberg/AP)

In a warning issued yesterday, the California Department of Health seemed to state the obvious: “CDPH strongly recommends against the intentional exposure of children to measles,” the agency said. “It unnecessarily places the exposed children at potentially grave risk and could contribute to further spread.”

But the words of caution may not have been obvious to everyone. The warning came after San Francisco radio station KQED reported a local woman offered to connect a mother of two unvaccinated children with someone who had the measles. The mother declined the offer and, to date, there is no evidence of anyone holding what the California media is calling a “measles party.”

California health officials are warning parents against intentionally exposing their children to measles, which they say could worsen an outbreak in the state. (Reuters)

“The basic notion is ‘This is my opportunity for my kid to get immune the old-fashioned way, the way God intended,’ ” epidemiologist Art Reingold of the University of California at Berkeley told KQED.

Aside from the KQED report, California officials say they haven’t heard of other instances of intentional exposure to measles, though a local public health officer did tell the Los Angeles Times his office received several inquiries about the benefits of “natural immunity,” rather than immunity from a vaccine.

But if parents are considering a deliberate attempt to infect their children with the disease, it would not be the first time.

Before the introduction of the chicken pox vaccine in 1995, it was common for parents to host “chicken pox parties” when one of their children fell ill. The theory was that it was better for kids to get sick and get it over with, rather than waiting for the disease to come later in life.

But the practice didn’t die out with the invention of a vaccine. Instead, families who declined the vaccine continued to try to immunize their kid “in the wild.” A 2004 story in “Mothering,” a magazine that promotes “natural family living,” described one such party as “jubilant.”

Sharing sippy cups, whistles, and lollipops (sugar- and saccharine-free, of course), the wee revelers romped and stomped and ran amok as microscopic varicella viruses triggered the alarms of their mucous membranes, manufacturing ideal antibodies for a lifetime of immunity,” the story read. “We at the party were doing what we felt was safest, after weeding through the propaganda and rhetoric about America ‘s latest ‘Red Scare’: the deadly scourge of chickenpox panic.”

The strategy was popularized again during the 2009 swine flu pandemic, when the New York Times reported bloggers and even some doctors were weighing the benefits of self-infection. Inspired by a history of the 1918 Spanish flu epidemic — mild in a first wave and more deadly during the fall and winter — it seemed logical, if risky, to attempt to contract the disease’s milder strain. But most flu experts panned the idea.

“I think it’s totally nuts,” said Anne Moscona, a flu specialist at Cornell University’s Weill Medical College. “This is like the Middle Ages, when people deliberately infected themselves with smallpox. It’s vigilante vaccination — you know, taking immunity into your own hands.”

Soon, self-infection took to social media. In 2011, posts appeared on Facebook advertising mail-order lollipops infected with the chickenpox virus. That start-up was swiftly shut down by law enforcement — intentionally mailing infected items is a federal crime. Meanwhile, “pox party” groups have popped up on Facebook and local listservs.

Chickenpox is typically a mild illness, particularly for those who contract it while they’re young, so most deliberate infections are unlikely to go awry. But measles is another matter entirely. The disease hasn’t been endemic in the United States since the 1990s, so good data is hard to come by, but the Centers for Disease Control and Prevention reported 28 percent of cases in children under 5 resulted in hospitalization between 2001 and 2013. The hospitalization rate for the current breakout is around 15 percent.

“It doesn’t make sense to say I’d rather have my kids get the measles than the measles vaccine,” Reingold, the epidemiologist at UC-Berkeley, told the L.A. Times. “That’s based on misinformation that the measles is a benign childhood illness.”

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