title: Waning Tdap Effectiveness in Adolescents.
abstract: OBJECTIVE
  Because the effectiveness of diphtheria-tetanus-acellular pertussis (DTaP) vaccine wanes substantially after the fifth dose at ages 4 to 6 years, there is a growing cohort of adolescents who rely on tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis (Tdap) for protection against pertussis. Yet despite high Tdap vaccine coverage among adolescents, California experienced large pertussis outbreaks in 2010 and 2014. We investigated Tdap vaccine effectiveness (VE) and waning within Kaiser Permanente Northern California among adolescents exclusively vaccinated with DTaP vaccines.
  
  
  METHODS
  We modeled pertussis risk in relation to Tdap vaccination status among adolescents beginning on their 10th birthday. We estimated the hazard ratio (HR) for each subsequent year after Tdap compared with unvaccinated adolescents by using Cox regression, adjusting for calendar time, age, gender, race, and facility. We calculated VE as 1 - HR. We also treated time since Tdap vaccination as a continuous variable and estimated the change in the HR per 1-year increase since vaccination.
  
  
  RESULTS
  On the basis of 1207 pertussis cases, Tdap VE during the first year after vaccination was 68.8% (95% confidence interval [CI] 59.7% to 75.9%), decreasing to 8.9% (95% CI -30.6% to 36.4%) by ≥4 years after vaccination. Adolescents who were more remote from Tdap were significantly more likely to test positive for pertussis than were those vaccinated more recently (HR per year 1.35, 95% CI 1.22 to 1.50).
  
  
  CONCLUSIONS
  Routine Tdap did not prevent pertussis outbreaks. Among adolescents who have only received DTaP vaccines in childhood, Tdap provided moderate protection against pertussis during the first year and then waned rapidly so that litle protection remained 2-3 years after vaccination..
authors.affiliation: Northern California Kaiser Permanente Vaccine Study Center, Oakland, California nicola.klein@kp.org.
authors.forename: Nicola P
authors.initials: NP
authors.lastname: Klein
authors.affiliation: Northern California Kaiser Permanente Vaccine Study Center, Oakland, California.
authors.forename: Joan
authors.initials: J
authors.lastname: Bartlett
authors.affiliation: Northern California Kaiser Permanente Vaccine Study Center, Oakland, California.
authors.forename: Bruce
authors.initials: B
authors.lastname: Fireman
authors.affiliation: Northern California Kaiser Permanente Vaccine Study Center, Oakland, California.
authors.forename: Roger
authors.initials: R
authors.lastname: Baxter
mesh_terms: D000293:Adolescent; D002140:California / Q000453:epidemiology; D002648:Child; D016001:Confidence Intervals; D004165:Diphtheria / Q000453:epidemiology / Q000517:prevention & control*; D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines / Q000008:administration & dosage*; D004196:Disease Outbreaks / Q000517:prevention & control* / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D007115:Immunization Schedule; D008297:Male; D012189:Retrospective Studies; D013742:Tetanus / Q000453:epidemiology / Q000517:prevention & control*; D014611:Vaccination / Q000379:methods*; D014917:Whooping Cough / Q000453:epidemiology / Q000517:prevention & control*
chemical_list: D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines