Vaccine refusal and hesitancy: An agent-based modeling approach

Exemptions from and alternatives to the required childhood immunization schedule have increased in the past decade with growing parental concerns about the safety of vaccines and their alleged, if unproven, link to autism and other health risks. Understanding how parents make the vaccination decision on behalf of their children is an important component of childhood infectious disease prevention policies. This study uses multiple data sources to inform an agent-based model of the vaccination decision and the resulting spatial and social clustering of unvaccinated children within certain neighborhoods and physician practices. The model is populated by agents (parents) who are assigned characteristics including vaccination preferences, network homophily, and physician preferences. In each tick of the model, agents make decisions about socializing with other agents, choosing a physician practice, and adhering to the vaccine schedule. Decision rules are based on the agent's characteristics as well the characteristics of nearby agents and physicians. The model output reveals the distribution of unvaccinated children in neighborhoods and physician practices over time and under varying scenarios of agent characteristic distributions and decision rules. The model can identify triggers or tipping points that result in particularly risky clusters of non-vaccination within certain groups. These clusters have implications both for the risk of disease outbreak and policy and program interventions to preserve herd immunity. The model can also be used to test competing policy interventions related to immunization coverage.