Control measures used to limit the spread of infectious disease often generate externalities. Vaccination for transmissible diseases can re- duce the incidence of disease even among the unvaccinated, whereas antimicrobial chemotherapy can lead to the evolution of antimicro- bial resistance and thereby limit its own eectiveness over time. We integrate the economic theory of public choice with mathematical models of infectious disease to provide quantitative framework for making allocation decisions in the presence of these externalities. To illustrate, we present a series of examples: vaccination for tetanus, vaccination for measles, antibiotic treatment of otitis media, and antiviral treatment of pandemic in uenza.