The study found that individuals with high vaccine hesitancy placed higher importance on moral concepts of purity and liberty than other moral foundations.

When faced with parents who are hesitant with regards to vaccinating their children, physicians often trot out the same aphorisms.  "Vaccines protect your children from harm", "vaccines protect society". But research has shown that, far from being persuasive, individuals who are hesitant with vaccination to begin with may become more entrenched in their beliefs when they are confronted with these types of arguments.

Now a new study, appearing in Nature Human Behavior, may tell us why, and it has to do with a concept called moral foundations theory.

Moral foundations theory states that we judge what to believe based upon the way in which the belief violates one of six moral principles.

Conservatives tend to judge the rightness of something by whether it violates their sense of loyalty, respect for authority, or purity. Liberals tend to judge the rightness of something in terms of whether it fails to protect people from harm or violates fairness. Violations of individual liberty seem to be important to certain members of both camps.

Of course, any individual person can value these moral foundations more or less than others. I took the standard survey to assess my moral foundations.

I score pretty low on the purity axis, which means I don't tend to judge the rightness of a belief based on whether it is "impure" or "unnatural". I focus more on whether it is fair or whether it protects individual liberty.

What does this have to do with vaccines? Well parents who are hesitant about vaccines don't divide neatly along political lines – but they do divide quite well along moral foundations.

Researchers conducted two independent studies including a total of 1,471 adults with at least one child under age 13. They asked standardized questions to gauge vaccine hesitancy and also measured their moral foundation scores using the same tool that I did.

 
What you see explains a lot. The parents who are skeptical of vaccinating their children put high value on the concept of purity – they don't like the idea of putting something "unnatural" into their children. They value liberty – they want the choice of what goes into their kids. And appeals to authority – i.e. doctors – are not going to be very effective.

To convince these individuals, the authors suggest, you need to appeal to concepts like purity and liberty.  Instead of saying "vaccines protect your children" the authors suggest language like “Keep your child pure of infections – Vaccinate!”.  This has a Dr. Strangelove feel that doesn't work too well for me – but we've all seen that purity is not my strongest moral foundation.

If it works for you, well, that's only fair.