Richard Robb—

In fall 2018, measles returned to New York City. It was hardly surprising, given the alarmingly widespread resistance to vaccination. According to a recent survey, 2% of Americans believe vaccines are unsafe and ineffective and another 6% believe the side effects of vaccination outweigh the benefits. Many antivaxxers maintain that childhood vaccinations for measles, mumps, and rubella (MMR) cause autism, even though the single study that made this claim was long ago discredited. 

In early September, 2019, Mayor de Blasio announced that the outbreak had officially ended. How did the City overcome antivaxxer beliefs and get reluctant parents to vaccinate their children? 

Although the City did launch an education campaign, that’s not what did the trick. Studies have shown that when confronted with the data, rebellious parents refuse to change their minds. In a large randomized trial, researchers tried four interventions. In the first, they explained that no evidence links the MMR vaccine to autism. In the second, they explained the dangers of measles, mumps, and rubella. In the third, they recounted the story of an infant whose life was imperiled by measles. Finally, they showed images of children sick from a disease the vaccine would have prevented. Compared to a control group, none of the subjects grew more willing to vaccinate their children, and graphic images of sick children actually strengthened parents’ belief that the MMR vaccine causes autism.

Why would parents cleave to a false belief that endangers their children? Let’s take a moment to consider why people adopt certain beliefs and not others in the first place. 

One sick person self-medicates with natural remedies while another strictly follows the doctor’s orders. A third rejects treatment altogether and relies on prayer. All three believe they are doing the right thing.

Faith in alternative medicine may stem from deeply held counter-culture principles, mystical beliefs in the body’s self-healing powers, or distrust of the medical establishment. This faith may have been reinforced by a personal experience in which alternative medicine seemed to work. Conviction in modern medicine goes together with an opposite constellation of beliefs: scientific evidence is the highest standard, and the system that generates this evidence and delivers therapies to patients can be trusted. And the third person, who believes events are in divine hands, might rely on the experience of previously answered prayers. She rejects the scientific method because she believes that God works in mysterious ways. 

Which of these individuals benefits from her belief? Should we expect any of them to? In principle, a professed belief in the side effects of vaccinations could serve as a convenient excuse for rational parents with a firm grasp on their own self-interest. Vaccinating children protects them from disease and prevents them from spreading disease to others. A selfish person who cared about only her own child’s welfare might prefer that all other children get vaccinated instead, sparing her the inconvenience. But with measles a very real threat—particularly in New York City, where 650 cases were diagnosed between October 2018 and September 2019—this theory doesn’t hold up. If everybody else can’t be trusted to vaccinate their children, then the rational parent must vaccinate her own.

The diversity of opinion in the world is astonishingly vast—far vaster than we would expect if belief adoption really were rational. Rather than formulating hypotheses, then checking them against empirical evidence to ensure we adopt only the most accurate ones, we pick beliefs that appeal to us. They are the style of thing we like to believe and, in the words of American pragmatist philosopher Charles Sanders Peirce, “agreeable to reason.” Each of us grounds our beliefs in other beliefs we already hold and favors experiential knowledge over equally valid knowledge gained secondhand. We find ways to dismiss arguments to the contrary. 

It’s unusual for people to change their minds and doubly unusual for them to change their minds quickly. According to legend, economist John Maynard Keynes quipped, “When the evidence changes, I change my mind. What do you do, sir?” But this was rhetoric to intimidate adversaries into coming around to his side. Like most everyone, Keynes held reasonably consistent, cohesive views his entire life. 

And can we fault him? Confidence in one’s own opinions is central to holding on to an identity. We tend to believe in ourselves. Even when they stand in the way of gratifying desires, our beliefs are not up for sale. As Popeye the Sailor Man declares, “I yam what’s I yam.”

This perhaps helps explain the tenacity with which anti-vaxxers have clung to a single, flawed study. A person committed to the idea that pharmaceutical companies behave recklessly might welcome a study purporting to link autism and vaccination, however flawed. Even after the study was discredited, such a person might defend it and dismiss the countervailing evidence as a corporate conspiracy. Rumors might circulate of dark forces suppressing studies that confirmed a statistical link. To such a person, the story of one child who showed signs of autism after being vaccinated would be persuasive. She just doesn’t like vaccines, and hates being told what to do. 

This means a viable solution requires more than an education campaign. One more lecture, one more attempt at “Anti-vaxxers, listen here!” is not going to work when all the previous ones have failed. As Walt Whitman observed, “Logic and sermons never convince.”

In New York City, I suspect it was instead force that did the trick. Last April, the mayor ordered mandatory vaccinations in the most afflicted parts of the City, backed up by $1000 fines for noncompliance. In June, the New York State legislature rescinded the religious exemption that had allowed unvaccinated children to attend school. There you have it.

This summer, Germany and Italy passed similar measures, making MMR vaccination mandatory for children to attend school and imposing fines of up to €2500 for noncompliance. That’s an example for Colorado and Idaho, where more than 10% of kindergarteners are unvaccinated. California state laws allowing 12-year-olds to obtain confidential vaccinations for HPV and Hepatitis B without their parents’ consent have Peirce’s pragmatism on their side. “My parents don’t know what they’re talking about” is squarely the style of thing a teenager likes to believe.

Richard Robb is professor of professional practice in international and public affairs at Columbia University and CEO of the investment firm Christofferson, Robb & Company, which he cofounded in 2001.

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