This paper analyzes a simple model of infectious disease where the incentives for individuals to reduce risks through endogenous social distancing take straightforward cost-benefit form. Since disease is transmitted through social interactions, the threat of spread of infection poses a collective action problem. Policy interventions such as lockdowns, testing, and mask-wearing serve, in part, as substitutes for social distancing. Provision of a vaccination is the only intervention that unambiguously reduces both the peak infection level and the herd immunity level of infection. Adoption of vaccination remains limited in a decentralized equilibrium, with resulting reproductive rate of disease Rt > 1 at the conclusion of vaccination. Vaccine mandates yield increases in vaccination rates and corresponding reductions in future infection rates but do not increase expected payoffs to individuals.
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