“Wait and see” vaccinating behavior during a pandemic: a game theoretic analysis

Abstract

During the 2009 H1N1 pandemic, many individuals adopted a “wait and see” approach to vaccinating until further information was available on the course of the pandemic and emerging vaccine risks. This behaviour implies two sources of strategic interactions between individuals: both perceived vaccine risk and the probability of becoming infected decline as more individuals become vaccinated. Here we analyze the outcome of these two strategic interactions by combining game theory with a mathematical model of disease transmission during an outbreak of a novel influenza strain. We include a case where perceived vaccine risk declines according to the cumulative number of individuals vaccinated. A common Nash equilibrium strategy exhibited by this model is a “wait and see” strategy where some individuals delay the decision to vaccinate, relying on the herd immunity provided by early vaccinators who also act as “guinea pigs” that validate the safety of the vaccine. The occurrence of “wait and see” strategies leads to a higher disease burden than occurs under socially optimal vaccine coverage. The model also exhibits both feedback and feed-forward processes. Feedback takes the form of individuals adjusting their vaccinating behaviour to accommodate changing transmissibility or risk parameters. Among other effects, this causes in the epidemic peak to occur at approximately the same time across a broad range of R0 values. Feedforward takes the form of high initial perceived vaccine risk perpetuating high perceived vaccine risks (and lower vaccine coverage) throughout the remainder of the outbreak, when perceived risk declines with the cumulative number vaccinated. This suggests that any effect of risk communication efforts at the start of a pandemic outbreak will be amplified compared to the same level of risk communication effort distributed throughout the outbreak, since any reductions in initial perceived risk will also result in reduced perceived risk throughout the outbreak.