The question of how to convince people to vaccinate their kids against easily preventable diseases came to a head earlier this year, when a measles outbreak that began last December at Disneyland sickened nearly 150 Americans and a similar number of Canadians. That incident, along with a growing number of outbreaks of pertussis, the virus that causes whooping cough, has perhaps changed the minds of some anti-vaxxers. Yet convincing doubters that vaccines are safe remains an uphill battle.
But if arguing for the safety of vaccines doesn't work, maybe confronting people with the risks of vaccine-preventable diseases will, according to a new study.
Most of those who got sick in the recent outbreaks had not been vaccinated, a fact that led California State Senators Richard Pan and Ben Allen to sponsor a bill to ban almost all exemptions from school vaccination requirements. Many praised Pan and Allen's work, but there was a backlash as well. Pan now faces a recall effort for his bill, and few in the anti-vaccine camp seem to have changed their minds. What gives? It's not that evidence of vaccines' safety is hard to find. Multiple studies over the last decade or so confirm that there's no link between vaccination and autism, to use just one particularly infamous example.
"Countering people's beliefs with evidence ... is just not a very effective way to change attitudes," says Zachary Horne, a psychology graduate student at the University of Illinois—Urbana-Champaign, and lead author of this new study that deals with changing anti-vaxxers' minds. He says that's probably because of confirmation bias—the tendency we all have to avoid or ignore information that's inconsistent with what we already believe.
"Countering people's beliefs with evidence is just not a very effective way to change attitudes."
On the other hand, "directing their attention to the consequences of not vaccinating" and using personal accounts and images of sick children will change minds, Horne says. "That's information they probably avoided because of confirmation bias."
Horne and colleagues from the University of Illinois and the University of California–Los Angeles, tested that alternative approach on 315 Americans recruited through Amazon.com's Mechanical Turk, a popular crowdsourcing website that's also proven to be a valuable source of subjects for academics' experiments. Participants first rated on a scale of one to six how strongly they agreed with a series of statements, such as "vaccinating healthy children helps protect others by stopping the spread of disease." The researchers averaged those ratings to create a six-point vaccines attitudes score.
Next, the researchers randomly assigned their subjects to one of three groups: One group that read expert opinions and research summaries debunking the connection between autism and vaccination; a control group that read about the costs and benefits of bird feeders; and a third group that read the story of a 10-month-old boy fallen ill with a life-threatening case of measles, and looked at pictures of children with measles, mumps, and rubella taken from the Centers for Disease Control and Prevention catalog of images of vaccine-preventable diseases. Afterwards, each participant took the vaccine survey again, so that the researchers could compare scores before and after.
Horne and his team found that trying to correct beliefs about an autism-vaccination link had about as much ability to correct inaccurate beliefs about vaccines as reading about bird feeders—which is to say, none.
But telling the stories of children sick with measles, mumps, or rubella using words and pictures did have an effect, especially on those most skeptical of vaccines' safety and effectiveness. On average, people were about a quarter of a point more pro-vaccine after seeing those stories, while the most skeptical—those in the bottom third on the initial vaccine attitudes score—were about six-tenths of a point more in favor of vaccination. Stories of sick children didn't completely change vaccine skeptics' minds, but they did make a significant dent, Horne says.
Brendan Nyhan and Jason Reifler, political scientists who've published several recent studies of attitudes toward vaccines, say they're "excited" by these results and "hope to see more studies like this in the future," they write in a joint email. "We're encouraged that [Horne and colleagues] find messages about the dangers of communicable diseases are effective in improving vaccine attitudes."
Still, questions remain. In a study published last year, Nyhan, Reifler, and two colleagues provided people with information debunking myths about flu vaccines—the same information, in fact, as Horne's team had used, but with rather different results. Refuting claims of a link between measles vaccination and autism reduced the number of parents who said they'd vaccinate their children, Nyhan and Reifler's team found, and stories and images of sick children actually strengthened beliefs in dangerous side effects associated with vaccines. The same goes for flu vaccines, according to a separate study Nyhan and Reifler published in January.
Nyhan, Reifler, and Horne agree that differences in exactly how the studies were carried out probably explain why they achieved different results. Horne's team, for example, showed their subjects both the sick child's story and images of sick children, while Nyhan and Reifler split the story and images between two separate groups. Horne says that by showing everything at once, participants in his study may have received a message with more punch, which would explain why they were more likely to change their minds.
"Future research should consider the extent to which design differences between the two studies help explain the somewhat different conclusions the two studies reach, which will help us reach our shared goal of better understanding vaccine attitudes and behavior," Nyhan and Reifler write.