When outbreaks of diseases that can be prevented by vaccines, such as measles, occur despite the availability of effective vaccines, it’s easy to blame parents who choose not to vaccinate. We might see them as misguided or influenced by misinformation. However, as experts in vaccine policy and health economics, we believe the decision not to vaccinate goes beyond misinformation or hesitancy.
Instead, it involves a concept known as game theory, a mathematical approach that helps explain how reasonable individuals can make decisions that lead to outcomes harmful to the public. Game theory shows that vaccine hesitancy isn’t a moral failure but a predictable result of a system where individual and collective incentives are not aligned.
Game Theory and Vaccination Decisions
Game theory studies how people make decisions that depend on others’ actions. Nobel Prize-winning mathematician John Nash, who was portrayed in the movie A Beautiful Mind, demonstrated that in many situations, decisions that seem rational on an individual level can lead to worse outcomes for everyone.
Vaccination decisions offer a clear example of this. When a parent decides whether to vaccinate their child against measles, they weigh the small risk of side effects against the risk of the disease. But crucially, the risk of the disease depends on other parents’ vaccination choices.
If most people vaccinate, herd immunity—where enough people are vaccinated to prevent the disease’s spread—protects everyone. However, once herd immunity is achieved, some parents may feel that not vaccinating is the safer choice for their child, since the disease is less likely to spread. This tension between individual decisions and collective welfare means that relying solely on individual choice doesn’t always lead to public health success.
The Free Rider Problem
This situation creates what economists call a free rider problem. When vaccination rates are high, some individuals benefit from herd immunity without taking on the minimal risk of the vaccine themselves.
Game theory predicts that even with a perfect vaccine—one with zero side effects—voluntary vaccination programs will never reach 100% coverage. Once vaccination rates are sufficiently high, some people will choose to benefit from herd immunity and avoid vaccinating.
When vaccination rates drop, as they have in recent years, outbreaks become more likely. This has already happened in Texas, where a large measles outbreak occurred after vaccination rates fell in certain areas. One county’s vaccination rate dropped from 96% to 81% over just five years, below the 95% needed for herd immunity, creating ideal conditions for the outbreak.
The Slow Recovery
Game theory also shows that when safety concerns arise, vaccination rates decline rapidly. However, recovery takes longer. This happens because while many parents stop vaccinating at once when fears spread, rebuilding trust and overcoming the free rider problem is a slow process. Parents often wait for others to vaccinate first, further delaying recovery.
Media coverage and social networks influence perceptions of vaccination, potentially pushing communities closer to or farther from herd immunity. Vaccination decisions can also cluster in communities, creating areas with low vaccination rates that allow diseases to persist, even if overall rates seem adequate.
Shifting the Narrative
The decline in vaccination rates is not a result of moral failure, but rather a system failure. Blaming parents for being selfish can backfire, making them more defensive and less likely to change their views. Instead, health messages should acknowledge the tension between individual and collective interests, and work with, not against, the mental processes that guide decision-making.
Research suggests that people respond better to messages framing vaccination as a community responsibility, rather than emphasizing personal failure. A 2021 study showed that parents were more likely to consider vaccinating when messages addressed their concerns and emphasized community protection, as opposed to messages that implied selfishness.
Better Communication Strategies
To address vaccine hesitancy, clearer communication is essential. For example, emphasizing the risks of the disease—such as the 1-in-500 chance of death from measles—can help parents weigh the risks more effectively. In areas with high vaccination rates, maintaining trust is key, while in areas with lower rates, rebuilding trust should be a priority.
Consistency is critical. When health experts provide conflicting messages, people tend to become more suspicious. Using fear-based tactics can also backfire, pushing people to more extreme positions.
Local conversations about vaccination, particularly in schools, can help establish positive social norms. Parents who understand that vaccines protect vulnerable individuals, such as infants or those with medical conditions, may be more likely to see vaccination as a collective good.
Health care providers remain the most trusted source of vaccine information. By understanding game theory, providers can better address concerns, recognizing that most vaccine hesitancy stems from balancing risks rather than outright opposition to vaccines.
Related Topics
