People adopt diverse measures to protect from contagion. I propose a taxonomy of protection technologies, and present a model to study the implications of the technology on the prevalence of infections and on welfare at different levels of exposure. I find that the effect of aggregate exposure on prevalence and on protection inefficiencies depends crucially on the characteristics of the available protection technology. For example, under certain conditions the existence of a vaccine will lead to lower infection rates and smaller welfare costs of decentralization as the society becomes denser. I discuss the implications for disease eradication, the equilibrium consequences of antigenic drift, the desirability of interventions in the absence of universal vaccines, and coordination failures in protection.