The Spatial and Social Clustering of Vaccine Refusal: An Agent-Based Modeling Approach

Alison M. Buttenheim, University of Pennsylvania

Exemptions from the required childhood immunization schedule have increased in recent years with growing parental concerns about vaccine safety. Increased vaccine refusal rates have led, in turn, to more frequent outbreaks of vaccine-preventable diseases. Understanding how parents make the vaccination decision is an important component of childhood infectious disease prevention policies. In this paper, I use multiple data sources to inform an agent-based model of the vaccination decision and the resulting spatial and social clustering of unvaccinated children within neighborhoods, schools, and physician practices. This clustering has implications for outbreak risk and for the design of policy interventions to preserve herd immunity. The model demonstrates how the clustering of unvaccinated children is related to physician and peer preferences and degree of influence, mixing rules, and school and physician choice. The model can be used to evaluate competing policy recommendations to promote adequate vaccination adherence and protect children’s health.