Vaccine-Preventable Diseases and Individual Behavior: Deterministic vs Stochastic Outcomes

We analyze the determinants of individual vaccination decisions and their implications on the aggregate immunization coverage and disease prevalence. We show that the relation between key socio-health-economic and epidemiological parameters determines which of the several alternative outcomes may arise (unique and multiple stable equilibria, monotonic and fluctuating trajectories, chaotic dynamics, and path dependency). By comparing the deterministic dynamics with their stochastic counterpart, we also show that the deterministic approximation typically employed in economic epidemiology may lead to misleading conclusions about the true stochastic outcome because of the metastable properties of the stochastic system. Public policy, by affecting socio-health-economic parameters, may play a fundamental role in ruling out some undesired outcomes and promoting eradication.