Altruism, social interactions, and the course of a pandemic

Externalities and social preferences, such as altruism, play a key role in the choice of social interactions, which in turn affect the diffusion of a pandemic. We build a dynamic epidemiological model with endogenous social interactions in a frictional environment, also in a variant with heterogeneous agents and a network structure. Taking into account agents' endogenous behavior and altruism generates markedly different predictions relative to a naive epidemiological model with exogenous contact rates. Congestion and commitment inefficiencies arise, even under full altruism, and call for policy intervention. We derive the efficient allocation, and show how the Ramsey planner can mitigate the respective externalities.