The prevalence of asthma and allergic disease has increased in many countries, and there has been speculation that immunization promotes allergic sensitization. Bordetella pertussis infection exacerbates allergic asthmatic responses. We investigated whether acellular pertussis vaccine (Pa) enhanced or prevented B. pertussis-induced exacerbation of allergic asthma. Groups of mice were immunized with Pa, infected with B. pertussis, and/or sensitized to ovalbumin. Immunological, pathological, and physiological changes were measured to assess the impact of immunization on immune deviation and airway function. We demonstrate that immunization did not enhance ovalbumin-specific serum immunoglobulin E production. Histopathological examination revealed that immunization reduced the severity of airway pathology associated with sensitization in the context of infection and decreased bronchial hyperreactivity upon methacholine exposure of infected and sensitized mice. These data demonstrate unequivocally the benefit of Pa immunization to health and justify selection of Pa in mass vaccination protocols. In the absence of infection, the Pa used in this study enhanced the interleukin-10 (IL-10) and IL-13 responses and influenced airway hyperresponsiveness to sensitizing antigen; however, these data do not suggest that Pa contributes to childhood asthma overall. On the contrary, wild-type virulent B. pertussis is still circulating in most countries, and our data suggest that the major influence of Pa is to protect against the powerful exacerbation of asthma-like pathology induced by B. pertussis.