Local reactions after the fourth dose of acellular pertussis vaccine in South Australia.

OBJECTIVE To assess the reported rate of local reactions after administration of acellular pertussis vaccine (DTPa) according to dose number and type of pertussis vaccine (whole-cell or acellular) used for the primary course, and to document the severity and outcome of fourth-dose local reactions. DESIGN AND SETTING Retrospective review. Reports of adverse events after vaccination in South Australia between 1 January 1997 and 31 December 2000 were reviewed, and a questionnaire administered to all parents who reported a local reaction after the fourth dose of DTPa. MAIN OUTCOME MEASURES The number, and rate per 100 000 administered doses, of local reactions following the primary and booster doses of DTPa, and of local reactions after the fourth-dose in cohorts of children whose primary vaccinations were with either DTPw or DTPa. Redness and/or swelling at the injection site as reported by parents. RESULTS Of 581 reported adverse events after vaccination, 138 were local reactions after a pertussis-containing vaccine. Primary vaccinations with DTPa was a significant risk factor for a fourth-dose local reaction (relative risk, 6.7; 95% CI, 2.4-18.5). Parental questionnaires were completed for 45 of the 71 children (63%) with reported local reactions after the fourth dose of DTPa; extensive limb swelling was reported in 8 children (18%) and all except one child had recovered by the time of review. CONCLUSIONS Parents should be informed that children receiving booster doses of DTPa vaccine, after primary doses with DTPa, are at increased risk of local reactions (which tend to resolve spontaneously) but not of systemic effects. Studies should be initiated to investigate the pathogenesis and the risk of recurrence of local reactions to further improve vaccination schedules.