Scientists might have an explanation for the severe and surprising resurgence of whooping cough in the U.S. Whooping cough (also called pertussis) is caused by the bacterial pathogen Bordetella pertussis and results in roughly 195,000 infant deaths worldwide every year, mostly in the developing world. However, since the mid-1970s, there has been an alarming uptick in fatalities in industrialized nations despite ongoing vaccination efforts since the 1940s. Seeking a better understanding of this observation, Matthieu Domenech de Cellès and colleagues formulated mathematical models using age-specific pertussis incidence records from Massachusetts where an active surveillance program ensured a wealth of detailed information over a 16-year period (from 1990 to 2005). The researchers evaluated three possible scenarios: primary vaccine failure (the immunization entirely fails to protect a subset of individuals), failure in duration (the vaccine works well at first, but protection wanes over time), and failure in degree (the protection is not perfect, potentially because the bacteria evolves). Based on the incidence data from Massachusetts -- where adolescents and adults accounted for the majority of cases -- failure in duration (or vaccine waning) offered the best explanation for whooping cough resurgence in this region of the U.S. The authors conclude that incomplete vaccine coverage of adults in the past combined with waning vaccine protection, and not a vaccine incapable of inducing immunity, set the stage for disease resurgence. Further analysis revealed that school-aged children represent a particularly important transmission hub and may be a good focus for future vaccination efforts.