The population dynamics of disease transmission may interact with the kinetics of immunity to further generate counter-intuitive phenomena that may affect the potential impact of control programs. The introduction of pertussis vaccine has been implicated in the recent increase in whooping cough rates in adults.  Analysis of age-specific whooping cough rates in Massachusetts showed an increase in disease incidence in adults that was far greater than would be expected due to the reduction in the force of infection alone Lavine 2011. Natural immunity to pertussis wanes over one’s lifetime, though the duration of protective immunity following infection is a matter of dispute. The introduction of pertussis vaccination reduced the rate at which individuals experience their first infection as well as the rate at which immunized individuals were re-exposed to natural infection in the environment.  Natural exposure of previously immune individuals results in a boosting of immunity, analogous to a booster vaccine, that results in no disease but conveys additional protection.  The lowered prevalence of pertussis resulting from vaccination meant that many individuals lost their protective immunity prior to re-exposure and thus were not protected upon subsequent natural exposure.  The resulting increase in adult cases arises from the combined time-scales of waning immunity and subsequent natural encounter with pertussis.