  Seasonal influenza presents an ongoing challenge to public health. The rapid
evolution of the flu virus necessitates annual vaccination campaigns, but the
decision to get vaccinated or not in a given year is largely voluntary, at
least in the United States, and many people decide against it. In early
attempts to model these yearly flu vaccine decisions, it was often assumed that
individuals behave rationally, and do so with perfect information --
assumptions that allowed the techniques of classical economics and game theory
to be applied. However, the usual assumptions are contradicted by the emerging
empirical evidence about human decision-making behavior in this context. We
develop a simple model of coupled disease spread and vaccination dynamics that
instead incorporates experimental observations from social psychology to model
annual vaccine decision-making more realistically. We investigate
population-level effects of these new decision-making assumptions, with the
goal of understanding whether the population can self-organize into a state of
herd immunity, and if so, under what conditions. Our model agrees with
established results while also revealing more subtle population-level behavior,
including biennial oscillations about the herd immunity threshold.
