When outbreaks of vaccine-preventable diseases such as measles occur despite highly effective vaccines being available , it’s easy to conclude that parents who don’t vaccinate their children are misguided, selfish or have fallen prey to misinformation.
As professors with expertise in vaccine policy and health economics , we argue that the decision not to vaccinate isn’t simply about misinformation or hesitancy. In our view, it involves game theory , a mathematical framework that helps explain how reasonable people can make choices that collectively lead to outcomes that endanger them.
Game theory reveals that vaccine hesitancy is not a moral failure, but simply the predictable outcome of a system in which individual and collective incentives aren’t properly aligned.
Game theory meets vaccines
Game theory examines how people make decisions when their outcomes depend on what others choose. In his research on the topic, Nobel Prize-winning mathematician John Nash , portrayed in the movie “ A Beautiful Mind , showed that in many situations, individually rational choices don’t automatically create the best outcome for everyone.
Vaccination decisions perfectly illustrate this principle. When a parent decides whether to vaccinate their child against measles, for instance, they weigh the small risk of vaccine side effects against the risks posed by the disease . But here’s the crucial insight: The risk of disease depends on what other parents decide. If nearly everyone vaccinates, herd immunity – essentially, vaccinating enough people – will stop the disease’s spread. But once herd immunity is achieved, individual parents may decide that not vaccinating is the less risky option for their kid.
In other words, because of a fundamental tension between individual choice and collective welfare, relying solely on individual choice may not achieve public health goals.
