EFFICACY OF ACELLULAR PERTUSSIS-VACCINE IN YOUNG INFANTS

A prospective study of a pertussis outbreak in a residential facility was done. Among 19 residents aged less-than-or-equal-to 2 years, 10 children were unimmunized and 9 were immunized with acellular pertussis vaccines. Of the 10 unimmunized children, 7 acquired laboratory-confirmed pertussis (four-fold titer rise, positive culture, or both); of these, 6 developed typical symptoms. Eight of the 9 immunized children acquired laboratory-confirmed infections, and 1 of these developed typical symptoms. No difference in infection was noted between the unimmunized and immunized groups (7/10 vs. 8/9, respectively), but a significant difference was observed in the development of symptoms (6/ 10 vs. 1/9, P < .05). Also, the isolation rate of Bordetella pertussis seemed to differ between the two groups (6/10 vs. 2/9, P = .12). In this population, acellular pertussis vaccine did not prevent infection with B. pertussis but protected most young infants from the onset of clinical symptoms.