The role of vaccine effectiveness on individual vaccination decisions and welfare

This paper examines a theoretical model designed to characterize a static, individual vaccination decision environment. I identify and characterize both equilibrium and socially optimal vaccination behavior and determine how this behavior changes as the effectiveness of the vaccine changes. I also evaluate the individual and social welfare implications of a change in vaccine effectiveness. I find that under certain conditions, an increase in vaccine effectiveness can decrease the number of agents vaccinating in equilibrium due to the positive external effects of vaccination. Notably, it is also possible for individual and total welfare to decrease. This is an undesirable, and perhaps unexpected, consequence of better vaccines. Fortunately, welfare at the social optimum always increases as vaccine effectiveness increases. However, equilibrium behavior often falls short of the social optimum due to the positive externalities created by vaccinating.