This paper develops a model of human interaction that provides microfoundations for a gravity equation for international trade and a multi-country Susceptible-Infected-Response (SIR) model of disease dynamics. We study how decreases in technological and man-made barriers to trade and labor mobility affect the rate at which human beings interact at short and long distances, and the consequences of these interactions for trade flows across countries and for welfare. We examine the implications of these changes in cross-border human interactions for the spread, persistence and human toll of epidemics. We consider various versions of our model, including some in which the rate of human interactions responds to the outbreak of a pandemic, through general equilibrium effects from changes in relative labor supplies and through individual behavioral responses to the threat of infection. Global flows of goods and of human beings interact with the spread of a pandemic in a number of subtle ways.