Scientists disagree on whether showing pictures of kids with measles is helpful.

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Can skeptical parents be persuaded to vaccinate?

The beloved novelist and children's author Roald Dahl once wrote an open letter describing how his daughter Olivia suffered from measles when she was 7 years old. Olivia seemed to be recovering, Dahl wrote, and he was sitting on her bed, teaching her how to build animals out of pipe cleaners, when he noticed that she had trouble coordinating her fingers' movements.

"‘Are you feeling all right?’ I asked her."

"‘I feel all sleepy,’ she said."

"In 1 hour she was unconscious. In 12 hours she was dead."

That happened in 1962, 1 year before the measles vaccine was developed. The virus had caused Olivia's brain to swell—an often-fatal complication called measles encephalitis. Dahl wrote the letter for the Sandwell Health Authority in the United Kingdom in 1986, hoping it would help persuade parents to vaccinate their children. The letter began circulating again in 2015, when a large measles outbreak that began at Disneyland in Anaheim, California, sickened more than 100 children.

Are such emotional stories about the danger of childhood diseases the right way to convince parents wary of vaccines? Yes, says Paul Offit, a pediatrician and head of the Vaccine Education Center at the Children's Hospital of Philadelphia in Pennsylvania. "I think we are compelled by fear more than reason," he argues. "You have to make parents realize that their choice isn't a risk-free choice."

No, says Gary Freed, a pediatrician studying public health at the University of Michigan in Ann Arbor. Increasing parents' anxiety may end up making them less likely to immunize their children, he warns. "We have to figure out a way to bring down fear rather than try to fight fear with fear."

Welcome to the fraught, complex challenge of trying to get parents to do what's right for their kids. Immunization is generally considered one of the safest and most effective public health strategies. The World Health Organization estimates that vaccines save 2 million to 3 million lives each year. But some parents aren't so sure they want their own children injected. Immunization rates are dropping in many countries, and vaccine-preventable diseases still cause big outbreaks, even in the developed world. Meanwhile, a small but vocal community is spreading misinformation about vaccines and demonizing proponents of immunization. (Google "Paul Offit" and one of the first pictures that comes up is his face with the words "WANTED FOR GENOCIDE.")

The question of how to win over parents has spawned a research field of its own, but the studies often have a limited scope, differ in approach, and contradict one another. "It's hard to say how much we actually know," says Cornelia Betsch, a psychologist at the University of Erfurt in Germany who studies vaccination decisions. Still, the work offers some clues on what works, scientists say. And persuasion isn't the only strategy; just making vaccination easier—or harder to refuse—also can have an important impact.

Gabrielle Barquin holds her daughter Sophie, 4, who was getting vaccinated against measles at the Miami Children's Hospital in Florida in 2015.

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When it comes to the Roald Dahl approach, both Freed and Offit can point to research supporting their views. In a 2015 study, researchers split 315 people into three groups. One received information debunking the myth that vaccines cause autism; the second, scientific reading material unrelated to vaccines; and the third, pictures of children suffering from mumps, measles, or rubella, along with a parent's description of a child's illness. In a follow-up questionnaire, the third group viewed vaccines more favorably than before; the others did not.

In a 2014 study, Freed also confronted parents with scary pictures and a tragic story. "I would have bet dollars to doughnuts that that would have a positive impact on their decision to vaccinate," he says. But the parents ended up more convinced that the measles vaccine can be dangerous. The material may have just increased parents' overall anxiety level, Freed speculates.

Stories about sick children might not work on some parents for several reasons, says Betsch, including a quirk of the human mind called omission bias. People tend to feel that a bad outcome they caused through action is worse than one caused by omission, or doing nothing. In one study, parents rated a vaccination-triggered fever as worse than one caused by illness. That may lead some to reject vaccination, Betsch says: "That way, if something happens it's not their fault, but fate."

Still, Betsch believes the Dahl strategy can be useful with some parents, particularly those who skip vaccines more out of convenience than concerns about their safety. When she reanalyzed data from the 2015 paper, she found that only 21 of the 315 participants held antivaccine views. Those people's minds weren't changed; the ones who were convinced were the "fence-sitters," those neither for nor against vaccination. Betsch's conclusion: Forget about hardcore antivaxxers, but focus on those who haven't made up their minds. That group, she says, can be convinced both by highlighting the risks of disease and by correcting misinformation.

Choosing where to focus your efforts is important, says Freed, because doctors have limited time to talk to parents. Offit says he can often tell within 30 seconds whether it's worth arguing. If parents are convinced of outrageous claims and think they already know everything, "I just bail," he says. "I know it's not worthwhile." Freed agrees but notes that giving up on hopeless cases can be hard: "These are kids. It's not their fault their parents refuse vaccines."

A matter of trust

A 2016 survey in 67 countries found that trust in vaccines is high overall but varies by country. Safety concerns were highest in Europe and Russia; in France, 41% disagreed with the statement that vaccines are safe.

CREDITS: (MAP) J. YOU/SCIENCE; (DATA) HEIDI LARSON ET AL., EBIOMEDICINE

Some researchers have studied the reasons why parents don't vaccinate their kids, in hopes of finding clues to the best strategy. Many parents talk about rumored health risks from immunizations or their negative view of the pharmaceutical industry, for instance, but those may not be the true reasons, says psychologist Stephan Lewandowsky of the University of Bristol in the United Kingdom. He says that's a lesson from his work on climate change doubters, whose real driver often isn't their beliefs about the role of carbon dioxide but rather their conservative political views.

In a study published in PLOS ONE, Lewandowsky reported that free-market ideology is a strong predictor of antivaccine sentiments; many libertarian parents oppose vaccinations, seeing them as infringing on parents' rights. (Despite popular perceptions, Lewandowsky found little evidence overall of a link between vaccine resistance and left-wing political views.) Understanding the political undercurrent is important, he says, because it can help choose the messenger: "Ideally you would want a bona fide, well-respected conservative who is speaking out in favor of vaccination." Nobody seems willing to take on that role, he adds.

Less surprisingly, Lewandowsky also found a "shockingly high" correlation between conspiratorial thinking and vaccine rejection. "It is much higher than for climate change or genetically modified foods," he says. On Infowars, a right-wing website that U.S. President Donald Trump has praised, parents find headlines such as "Most Dangerous Flu Vaccine Ever Being Pushed on the Public" and "Is the UN Using Vaccines to Secretly Sterilize Women All Over the Globe?"

Such myths pose a problem to scientists because believers often interpret evidence against a conspiracy theory as further proof of cover-ups, which means attempts to debunk a conspiracy can backfire, Lewandowsky says. Scientists should still make the effort, he adds—not for the conspiracy thinkers, but for everyone else. "Debunking is important because if you don't debunk, then the antivaxxers have talking points," he says.

Experience has taught the same lesson to Roel Coutinho, a former director of the Netherlands's national coordination center for infectious diseases in Bilthoven. When the vaccine against human papillomavirus was rolled out in the Netherlands in 2009, a surge of opposition and rumors about serious side effects took Coutinho and others by surprise. "It's like a virus, it's contagious, the message spreads very fast, and if it's already very big, there is not much you can do about it," he says. Authorities have to act fast, he says, by taking even the most bizarre rumors seriously and countering them with facts. "You cannot simply say, ‘This is bullshit,’ even though you sometimes think it is. That doesn't work."

Several studies have shown that casting doubt on the credibility of sources of misinformation can help, Lewandowsky says. That's why it's still important to point out that an influential 1998 paper in The Lancet claiming to show a link between autism and vaccines was fraudulent and has been retracted, he says. (Its main author, Andrew Wakefield, was barred from treating patients in the United Kingdom.) "It was such a paradigm case of overt fraud that dismissing Wakefield is relatively easy now, and we have to do that," Lewandowsky says.

Another helpful tactic is appealing to consensus among scientists. A 2015 paper in BMC Public Health showed that telling parents that "90% of medical scientists agree that vaccines are safe and that all parents should be required to vaccinate their children" significantly reduced concern about vaccines. (Similar results have been shown for climate change.) That approach has the advantage that it avoids repeating myths in order to debunk them, which some studies suggest can reinforce the myths.

Betsch has explored the power of telling parents that their choice could hurt other people's children. As long as enough people are vaccinated, even those who won't or can't get a vaccine—for medical reasons, for instance—are protected in an effect called herd immunity. When too many people refuse a shot, herd immunity breaks down and vulnerable people get sick. That happened with a 6-year-old German girl who died from a rare measles complication last year; she was infected when she was 3 months old, too young to be vaccinated.

Betsch's study recruited more than 2000 participants from three Western and three Asian countries. Some were informed about herd immunity, either in a text or through an interactive game, whereas others weren't. All were asked about their intention to vaccinate against a fictional disease afterward. In South Korea, Hong Kong, and Vietnam, an average of 61% said they would get vaccinated, regardless of whether they had learned about herd immunity. In Germany, the Netherlands, and the United States, only 45% of those who weren't told about herd immunity would get the shot; for those who were, that number was 57%. The higher numbers in Asia might be due to the fact that people in collectivist societies adhere to norms more strictly, Betsch says—or perhaps the Asian participants were already aware of the benefits of immunization to the society as a whole. "Whatever the reason, the data shows that an appeal to herd immunity is especially important in individualistic societies," she says.

The science of persuasion may be uncertain, but immunization advocates have other approaches to help increase vaccine coverage. "People always talk about the antivaxxers, but there are so many things in the medical system that keep some people from getting immunizations," Betsch says. Some people delay or skip vaccines not because they are opposed to them, but simply because they find it hard to get an appointment at a convenient time. Making vaccinations as convenient as possible can further increase vaccination rates, Betsch says.

The opposite is also true. In the United States, parents have to get an exemption—on medical, religious, or philosophical grounds—if they want to send an unvaccinated child to school. According to a recently published study, states where that process is harder had higher vaccination rates. Michigan had a high rate of unvaccinated kids, but in 2015 it began requiring parents to consult with local public health departments to obtain a waiver, and exemptions plummeted by 35%.

Other factors are impossible to legislate, or even measure scientifically: the human interactions whenever a doctor meets a hesitant parent. Freed says being forceful is important. For instance, when people say it might be healthier for their kids to have diseases than not, he says he has a firm answer: "There are very few children paralyzed with polio who feel it was healthier for them to get the disease."

Offit agrees that doctors need to be more outspoken and proscriptive. His wife runs a private practice and initially wasn't very successful in convincing wary parents, he says. "Then she basically laid it on the line: ‘If you can't do this, I can't see you. I can't stand that your child is at risk like this.’" Many more parents now agree to the shots, Offit says. "I think passion works."