Jenny McCarthy (Reuters/Fred Prouser)

Study: Trying to convince parents to vaccinate their kids just makes the problem worse

Why is it so hard to change a skeptic's mind?


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Lindsay Abrams
March 4, 2014 3:01AM (UTC)

So far as head-in-the-sand denialism goes, anti-vaxxers give climate deniers a run for their money as the most frustrating -- and the most dangerous. Despite a preponderance of evidence refuting a connection between vaccines and autism -- and despite the very real public health risks of choosing not to vaccinate -- anti-vaccine fervor is strong enough that 20 states allow personal-belief exemptions for enrollment in public school.

Is this all just a case of misinformation, as many researchers contend? Are parents really just that deferential to the all-knowing authority of Jenny McCarthy? According to a disconcerting new study in Pediatrics, it may be more complicated than that. Once people are convinced that vaccines are bad, researchers found, changing their minds is no longer just a matter of setting the record straight.

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Mother Jones has more on the study out of Dartmouth College, which evaluated the effectiveness of four different pro-vaccine messages:

The first message, dubbed "Autism correction," was a factual, science-heavy correction of false claims that the MMR vaccine causes autism, assuring parents that the vaccine is "safe and effective" and citing multiple studies that disprove claims of an autism link. The second message, dubbed "Disease risks," simply listed the many risks of contracting the measles, the mumps, or rubella, describing the nasty complications that can come with these diseases. The third message, dubbed "Disease narrative," told a "true story" about a 10-month-old whose temperature shot up to a terrifying 106 degrees after he contracted measles from another child in a pediatrician's waiting room.

All three of these messages are closely based on messages (herehere, and here) that appear on the CDC website. And then there was a final message that was not directly based on CDC communications, dubbed "Disease images." In this case, as a way of emphasizing the importance of vaccines, test subjects were asked to examine three fairly disturbing images of children afflicted with measles, mumps, and rubella.

The results showed that by far, the least successful messages were "Disease narrative" and "Disease images." Hearing the frightening narrative actually increased respondents' likelihood of thinking that getting the MMR vaccine will cause serious side effects, from 7.7 percent to 13.8 percent. Similarly, looking at the disturbing images increased test subjects' belief that vaccines cause autism. In other words, both of these messages backfired.

All discouraging, but the "Autism correction" message had the most perplexing results: The fact-based approach was successfully able to reduce misperceptions that vaccines cause autism, but it actually decreased parents' intent to vaccinate. More from MJ:

Looking more closely, the researchers found that this occurred because of a strong backfire effect among the minority of test subjects who were the most distrustful of vaccines. In this group, the likelihood of saying they would give their kids the MMR vaccine decreased to 45 percent (versus 70 percent in the control group) after they received factual, scientific information debunking the vaccines-autism link. Indeed, the study therefore concluded that "no intervention increased intent to vaccinate among parents who are the least favorable toward vaccines."

"We shouldn't put too much weight on the idea that there's some magic message out there that will change people minds," author Brendan Nyhan told LiveScience. We also, he added, need to be extra conscious about what messages we are sending out: it's once vaccination rates slip below a certain percentage (about 95% for measles) that "herd immunity" is threatened, making it possible for disease to spread. The last thing well-meaning public health officials want to do is tip the population in that direction.


Lindsay Abrams

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