“Vaccine hesitancy” is a delicate way of phrasing a serious public-health problem. The World Health Organization defines it as “delay in acceptance or refusal of vaccines despite availability of vaccination services.”

There’s a tendency to treat these vaccine-hesitant people as a monolith, the “anti-vaxers” who are putting everyone at risk. But people who don’t vaccinate aren’t just a homogenous mob of parents who fear toxins and want their kids to be exposed to chicken pox “the natural way.” There are a variety of reasons why people decide not to vaccinate, and a new paper by researchers at Rutgers University and Germany’s University of Erfurt and RWTH Aachen University, published in Policy Insights from the Behavioral and Brain Sciences, breaks down the psychology of four different types of non-vaccinators, in the hopes of finding effective strategies to change their minds.

* * *

The Complacent: These people tend to live in places where there aren’t many cases of vaccine-preventable diseases, so they don’t see the diseases as a threat. “Complacent people passively omit vaccination rather than actively decide against it,” the article reads. “Nobody gets measles anymore,” thinks Complacent Courtney, blowing off scheduling her daughter’s booster shot. Maybe they’ll go next month, when they have more time.

The Inaccessible: For some, vaccinating is more difficult than a short drive to the doctor’s office and a quick prick on the arm. They may live in places with a shortage of health-care resources, and have to travel a long way for an appointment. They may not have insurance. There may be a language barrier between the patient and the doctor. Often, when vaccination is inconvenient, “attitudes are not strongly against or in favor of vaccination ... which means that vaccination is not important enough to actively overcome barriers,” the researchers write. Inaccessible Ian lives in a rural area, and has to drive an hour and a half to see his doctor, who he pays out of pocket, because he doesn’t have insurance. He sees no reason to make the trip when his son’s perfectly healthy right now.

The Calculating: “They engage in an extensive information search for pros and cons of vaccination,” the article reads. “If the risk of infection is perceived to be lower than the risk of vaccination, the decision will be against vaccination … This can result in free-riding, that is, the idea that it is selfish-rational to omit vaccination as long as enough other individuals are vaccinated to keep the infection risk low.” Calculating Carl knows a lot about herd immunity. After his daughter was born, he spent hours online researching vaccines. Though he thinks vaccines are probably safe, he’s seen enough people questioning to have just a seed of doubt. And since his research tells him that as long as most people vaccinate, the whole population should be safe, he thinks, why expose his daughter to even the smallest risk if she’ll be protected anyway?

The Unconfident: These are the classic anti-vaxers, the ones who get the most attention. They don’t trust that vaccines are safe, they don’t trust the health system or the doctors telling them vaccines are safe, and/or they don’t trust the people who make the policies promoting vaccination. Whereas the calculating and the complacent have more of an ambivalent attitude toward vaccines, the unconfident feel negatively about them. Unconfident Ursula is worried. A friend of hers told her he knows someone whose kid was diagnosed with autism a few months after getting vaccinated. Though her doctor has assured her there’s no link between vaccines and autism, she doesn’t feel like he’s taking her concerns seriously enough. Her friend says he’s thinking about opting out of vaccinating his kids, and Ursula is starting to think maybe she should, too.

* * *

“We suggest that different types of non-vaccinators have different sets of ‘active determinants’ that influence their decisions,” the researchers write. “Furthermore, we propose that interventions should be targeted to these differences.”

For example, Inaccessible Ian needs structural help to make vaccinating easier and more affordable. A campaign that explains the risks of not vaccinating, and the benefits vaccines have for society, could change Calculating Carl's calculations, and it could shock Complacent Courtney out of her complacence. Calculating Carl could also be motivated by financial incentives.

Unconfident Ursula is the trickiest of the four characters, which is perhaps why so much media coverage has focused on people with her attitude. While a public-health campaign that shows vaccination as a norm might get Complacent Courtney to schedule an appointment, Unconfident Ursula, distrusting the health system as she does, might just dig in her heels. “If there is a perception of vaccination as a norm or coercion, reactance will lead to consciously counteracting this norm,” the study reads. The only suggestion that the researchers have for Unconfident Ursula is “debunking vaccination myths.” Unfortunately, research has shown that debunking myths doesn’t work—even if people grasp the information, it doesn’t make them more likely to vaccinate their kids.

Because changing the minds of Unconfident Ursulas is so difficult, the researchers here suggest focusing on the other three types as places where policy could make a difference. “There are a lot more interventions that promise to be effective for complacent, convenient, and calculating individuals whereas there is only one method that might be effective for those who lack confidence,” the researchers write. “Thus, efforts should be concentrated on motivating the complacent, removing barriers for those for whom vaccination is inconvenient, and adding incentives and additional utility for the calculating. These strategies might be more promising, economic, and effective than convincing those who lack confidence in vaccination.”