Current public health messages about vaccines may be not only ineffective but also counterproductive among people who are suspicious about the potential effects of vaccines, according to a study published online March 3 in Pediatrics.

Brendan Nyhan, PhD, assistant professor of government at Dartmouth College, Hanover, New Hampshire, and colleagues conducted an Internet-based survey experiment involving parents in the United States with children younger than 17 years living in their households. Participants were from a nationally representative Knowledge Networks group recruited by random dialing and address-based sampling.

The researchers conducted the survey in 2 waves. In the first wave, 2471 individuals (55.4% response rate) responded to questions about the health status of their children and their attitudes toward vaccines, as well as whether they had ever delayed or refused a recommended vaccine and how much they trust healthcare professions.

The researchers recontacted a subset of respondents, and of those, 1759 (88%) completed wave 2 of the survey, during which they were randomly assigned to receive 1 of 4 provaccine messages or a control message. The control message consisted of text about costs and benefits of bird feeding. The 4 provaccine messages were:

information to correct the misperception that the MMR vaccine causes autism,

information on disease risks and adverse events associated with MMR,

a disease narrative of a mother describing her infant son's experience with the measles, and

disease images depicting children with measles, mumps, or rubella.

The researchers used real messages "nearly verbatim" from the Centers for Disease Control and Prevention for much of the textual information.

The 3 key study outcomes were whether respondents thought the MMR vaccine causes autism, whether they thought MMR vaccine causes adverse effects, and whether the parents intended to get their next child vaccinated.

Although the "autism correction" message did reduce agreement that "some vaccines cause autism in healthy children" (adjusted odds ratio [aOR], 0.55; 95% confidence interval [CI], 0.38 - 0.79), it did not significantly reduce concerns regarding MMR vaccine adverse effects compared with controls (aOR, 0.81; 95% CI, 0.57 - 1.15).

Meanwhile, the message about disease risks and MMR adverse events had no significant effect on attitudes about the vaccines-cause-autism misperception (aOR, 1.15; 95% CI, 0.79 - 1.67) or on attitudes about whether MMR vaccine adverse effects (aOR, 0.93; 95% CI, 0.65 - 1.35).

The disease narrative by the mother "actually increased beliefs in the likelihood of serious side effects from MMR (aOR = 1.92; 95% CI, 1.33–2.77)," the researchers write.

Counterproductive

Perhaps most important, none of the intervention messages had a significant effect on increasing intentions to vaccinate. In fact, using logistic regression modeling, the researchers found that parents who received the autism correction message were almost half as likely as controls to vaccinate future children (aOR, 0.52; 95% CI, 0.32 - 0.84).

"Showing parents corrective information that MMR vaccine does not cause autism made them less likely to say they would vaccinate a future child with MMR. That effect was concentrated among parents with the least favorable attitudes toward vaccines, which is precisely the group that we're most concerned about from a public health perspective," lead author Dr. Nyhan told Medscape Medical News.

"There is a great deal of evidence that people are often motivated to defend their previous beliefs when they encounter information that conflicts with those beliefs," he continued. "In this case, it looks as if people were willing to accept that vaccines don't cause autism, but those parents with the least favorable attitudes toward vaccines might have thought that bolstered their attitude by bringing to mind other objections or concerns they have about vaccines, and the process ended up [with] them coming to feel more strongly opposed to vaccines than they otherwise would have been."

Pretest and Explore Pediatrician Role

The researchers suggest that future messages be pretested in ways such as this survey before being deployed. Also, they write, "Given that parents rate their childhood's doctor as their most trusted source of vaccine safety information," future research could focus on exploring whether pediatricians "would be an especially persuasive source" for parents on vaccines.

"We suggest in the article that one of the most promising areas for research is to see whether clinicians might be more effective messengers because they are so trusted by parents," Dr. Nyhan told Medscape Medical News. "Our study underscores that facts and evidence alone aren't necessarily sufficient or even effective. Clinicians could potentially be more effective or persuasive, but we need to do more research to find out if that's true.

"The bottom line," he said, "is we tend to overestimate the persuasiveness of scientific evidence and the extent to which existing messages have been evaluated empirically."

This research was funded by the Robert Wood Johnson Foundation Health and Society Scholars Program. The authors have disclosed no relevant financial relationships.

Pediatrics. Published online March 3, 2014.