Here we go again. And again. And again. A bad measles outbreak is currently hitting the area just north of Portland, Oregon, with 23 cases and a public health emergency declared. Another in Brooklyn (55 cases) has spread up the lower Hudson Valley north of New York City (116 cases). One just popped up in Atlanta. There were 17 other outbreaks (defined as three or more cases) across the United States last year. And things are far worse in Europe: 41,000 cases in the first six months of last year, including at least 37 deaths.

Just as predictably, along with each of these outbreaks has come the frustration from multiple sources that these illnesses, and the massive costs they impose on communities trying to rein things in, could have been avoided if only people vaccinated their children against this disease. Article after article decries the problem, explaining the safety of measles vaccination and terms like herd immunity. Rational appeals are peppered with scolding charges of “irrationality,” “science denial,” and “madness.” Appeals to reason and evidence seem logical, but the appeals themselves are also unreasonable in their own way: They deny what these continuing episodes should make clear to us—that reason and evidence alone are not what this is all about.

What might help break this cycle, or at least reduce its frequency? A remarkable study—which received far too little attention when it was published in Nature in late 2017—offers some hopeful insight. It gets to the heart of the problem, the underlying emotions and psychology that explain why bright and fully informed people can see the same set of facts—in this case about childhood vaccination—in such radically different ways. As with so many issues, our perceptions are not the product of the facts alone, but more a matter of how we feel about those facts.

In the study, Avnika Amin and Saad Omer of Emory University (and their colleagues) identify some of the fundamental motivations behind 1) vaccine hesitancy, defined as parents being concerned about vaccinating their kids according to recommended schedules (something 75 percent of pediatricians say they’ve experienced); and 2) outright vaccine refusal, which is fortunately less common and tends to be limited to communities where people share common beliefs. (Overall childhood vaccination rates in the U.S. remain high.)

To identify the roots of these beliefs and hesitancies, Amin and Omer went deeper than most other research on fear of childhood vaccines. Their research is based on moral foundations theory, which centers on the various basic moral codes by which we judge right and wrong and that shape our fundamental sense of how we should behave and how society should operate. These are the basic lenses through which we see the world, the behaviors of others, and the issues of the day, and they vary from person to person. Some of us put more emphasis on caring for others and not doing harm (e.g., concern for the poor and refugees, anger at the mistreatment of immigrants). Some of us put more emphasis on being fair and not cheating (e.g., anger at corrupt politicians). Some of us emphasize loyalty and are upset by betrayal (e.g., loyal Republicans reject climate change, liberals oppose nuclear power, violators are kicked out of the tribe). Some emphasize respect for authority (e.g., the self-declared patriotism of people angry at NFL players who kneel during the national anthem). Some emphasize purity and cleanliness and are upset by contamination (e.g., people upset by pollution). And some people prioritize personal liberty and bristle at the suppression of individual freedom (e.g., gun rights advocates, the Occupy Wall Street movement’s anger that the wealthy control everything). We all share many of these values, but some of us are more motivated by some of them than others. Which ones we prioritize depends on all kinds of aspects of our personalities, along with age and gender and other life circumstances, as well as the issue at hand.

Amin and Omer found that moral foundations theory helps explain vaccine hesitancy. In one study, they compared three groups of parents: those with little concern (73 percent of the 1,007 people surveyed), those with moderate concern (11 percent), and those with “high hesitancy” (16 percent). They found that parents with medium vaccine hesitancy were twice as motivated by the purity/degradation moral value as the low-concern parents. And they found that the high-hesitancy parents were twice as motivated by both the purity/degradation and the liberty/oppression values as the low-concern group. Even more importantly, none of the concerned parents, in either the moderate- or high-hesitancy groups, were motivated by the care/harm value. That’s the moral argument used to appeal to parents’ sense of civic responsibility—that their unvaccinated kid might make some other kid who can’t get vaccinated sick. Vaccine-hesitant parents are not motivated by this care-for-others value nearly as much, at least on this issue.

Let’s put this into more familiar language. Vaccine-hesitant parents frequently say they worry about putting something foreign into their children’s bodies, so young and pure. They talk about not wanting to put something unnatural into their pure children’s bodies. They worry that vaccines may contain “poisons” and “toxins” and “contaminants”, like thimerosal. That is the semantic expression of the purity/degradation moral value. The more deeply hesitant parents and outright vaccine refusers say these things too. But they also go further: They state that they don’t like the government or the medical community telling them what to do, which is a reflection of the liberty/oppression value, and that they don’t trust those institutions’ promises that vaccines are safe, which means that they aren’t motivated by the moral value of respect for authority (again, at least not on this issue).

There is more to the psychology of vaccine hesitancy than these moral codes. We are generally more concerned about risk to children than risk to adults. We are more worried about risks that are getting a lot of alarming coverage in the news or attention among our friends. We are inherently more concerned about risks that are human-made than risks that are natural. (Some parents are willing to expose their pure children’s bodies to measles itself because “that’s natural.”)

But what the Amin/Omer research shows us is that vaccine hesitancy is deeply connected to our emotions. Feelings shape the decisions we make, which suggests that more information alone isn’t going to change many hearts. It also tells us more than we ever knew about what vaccine-hesitant parents really care about, and those insights offer hope. We will never entirely eliminate fear of vaccines, which has been with us as long as vaccines themselves.

It’s true that some resistance is so entrenched that only higher hurdles for opting children out of vaccinating as a requirement for public school enrollment will do any good. But it’s still worth trying to persuade. If we can find ways to frame the case for vaccination that appeal to the moral values that motivate parents’ hesitancy, we’ll have more success convincing at least some of those mothers and fathers to make the emotionally difficult leap from their hesitancy to begrudging acceptance. That might reduce the frequency or severity of these outbreaks, move vaccination rates closer to levels that create “herd immunity,” and do kids and communities a lot of good.