Uncertainty in vaccination behavior: Social norms, network effects, and policy challenges

This study examines the role of social norms in vaccination decisions and their impact on optimal government policies, in contexts where uncertainty about the prevailing equilibrium may hinder the government’s ability to tailor incentives effectively. We explore the interplay between individual benefits, social conformity, herd immunity, and government intervention. Our model incorporates heterogeneous agents facing a binary choice: to vaccinate or not. Individual preferences vary based on their perceived disutility (inconvenience) of vaccination, the strength of social norms (network effects), and the presence of incentives. When network effects are weak (WNE), social norms increase vaccination uptake and provide indirect protection to unvaccinated individuals, indirectly improving their chances to free-ride. However, when network effects are strong (SNE), multiple extreme equilibria appear, leading to uncertainty about the emerging behavior (strongly in favor or against vaccination). While incentives can enhance vaccination levels under WNE, they may not fully eliminate the risk of undesirable low-vaccination traps under SNE. These findings highlight the limits of conventional policy tools in socially driven settings.