The influence of preschool pertussis immunization on an epidemic of pertussis.

Between 1988 and 1989 there were 896 reported cases of pertussis in Arizona. Of the 781 investigated cases 55 were identified in children younger than 5 years of age. Thirty-five percent of children between 6 months and 5 years of age were not fully immunized; 3 infants died. Approximately 50% of infected children between 5 and 14 years of age had not received 5 doses of pertussis vaccine. Of the 413 physician respondents to a questionnaire, fully 10% do not administer pertussis vaccine to preschool children because of parental, personal or other reasons. We hypothesize that the reservoir of pertussis-susceptible older children and young adults is augmented by this omission of the fifth diphtheria-tetanus toxoids-pertussis vaccine. Newer educational and vaccine strategies are necessary to prevent epidemics of pertussis.