Assessment of Tdap Vaccination Effectiveness in Adolescents in Integrated Health-Care Systems

Abstract

Purpose: Despite high national vaccination coverage with tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) vaccines among U.S. adolescents, rates of adolescent pertussis disease are increasing. We estimated the duration of protection after Tdap vaccination and the possible effects of the change from whole-cell to acellular childhood pertussis vaccines in the United States during the 1990s.

Methods: We conducted a retrospective cohort analysis among 11- to 18-year-olds enrolled in two integrated health-care delivery systems during 2005-2012. Cases met the Council of State and Territorial Epidemiologists' confirmed or probable definition or a polymerase chain reaction-positive suspect definition. We estimated vaccine effectiveness (VE) overall and by time since Tdap receipt. We stratified VE estimates by primary series pertussis vaccine received (based on birth year): mixed-vaccine cohort (1987-1997) and acellular vaccine cohort (1998-2001).

Results: The overall Tdap VE was 57% (95% confidence interval [CI]: 42%-68%); the VE in the mixed-vaccine and acellular cohorts was 65% (95% CI: 44%-78%) and 52% (95% CI: 30%-68%), respectively. Tdap VE within <2 years post vaccination (69%, 95% CI: 54%-79%) was significantly different from VE ≥2 years post vaccination (34%, 95% CI: 1%-55%, p value < .01). VE was significantly higher <2 years post vaccination compared with ≥2 years post vaccination in both mixed-vaccine (87%, 95% CI: 58%-96%, and 52%, 95% CI: 13%-73%; p value = .04) and acellular cohorts (62%, 95% CI: 41%-76%, and 21%, 95% CI: -30% to 52%; p value = .01).

Conclusions: Although Tdap vaccination remains the best pertussis prevention method for adolescents, protection wanes within 2 years regardless of the type of childhood primary vaccine. Vaccines with longer duration of protection could decrease pertussis burden.

Keywords: Adolescents; Pertussis; Vaccine effectiveness.