Post-licensure safety surveillance study of routine use of tetanus toxoid, reduced diphtheria toxoid and 5-component acellular pertussis vaccine

An observational post-licensure (Phase IV) retrospective large-database safety study was conducted at Kaiser Permanente, a US integrated medical care organization, to assess the safety of Tetanus Toxoid, Reduced Diphtheria Toxoid and 5-Component Acellular Pertussis Vaccine (Tdap5) administered as part of routine healthcare among adolescents and adults. We evaluated incidence rates of various clinical events resulting in outpatient clinic, emergency department (ED), and hospital visits during various time intervals (windows) following Tdap5 vaccination using 2 pharmacoepidemiological methods (risk interval and historic cohort) and several screening thresholds. Plausible outcomes of interest with elevated incidence rate ratios (IRRs) were further evaluated by reviewing individual patient records to confirm the diagnosis, timing (temporal relationship), alternative etiology, and other health record details to discern possible relatedness of the health events to vaccination. Overall, 124,139 people received Tdap5 vaccine from September 2005 through mid-October 2006, and 203,154 in the comparison cohort received a tetanus and diphtheria toxoid adsorbed vaccine (and no live virus vaccine) during the year prior to initiation of this study. In the outpatient, ED and hospital databases, respectively, we identified 11/26, 179/700 and 187/700 unique health outcomes with IRRs significantly >1.0. Among the same unique health outcomes in the outpatient, ED, and hospital databases, 9, 146, and 385, respectively, had IRRs significantly <1.0. Further scrutiny of the outcomes with elevated IRRs did not reveal unexpected signals of adverse outcomes related to vaccination. In conclusion, Tdap5 vaccine was found to be safe among this large population of adolescents and adults.