title: Waning immunity to pertussis following 5 doses of DTaP.
abstract: OBJECTIVE
  To assess the risk of pertussis by time since vaccination in children in Minnesota and Oregon who received 5 doses of acellular pertussis vaccines (DTaP).
  
  
  METHODS
  These cohort analyses included Minnesota and Oregon children born between 1998 and 2003 who had 5 DTaP doses recorded in state Immunization Information Systems. Immunization records and statewide pertussis surveillance data were combined. Incidence rates and risk ratios for pertussis were calculated for the 6 years after receipt of the fifth DTaP dose.
  
  
  RESULTS
  The cohorts included 224,378 Minnesota children and 179,011 from Oregon; 458 and 89 pertussis cases were identified in Minnesota and Oregon, respectively. Pertussis incidence rates rose each year of follow-up: 15.6/100,000 (95% confidence interval [CI]: 11.1-21.4) at year 1 to 138.4/100,000 (CI: 113.3-166.9) at year 6 (Minnesota); 6.2/100,000 (CI: 3.3-10.6) in year 1 to 24.4/100,000 (CI: 15.0-37.8) in year 6 (Oregon). Risk ratios increased from 1.9 (CI: 1.3-2.9) in year 2 to 8.9 (CI: 6.0-13.0) in year 6 (Minnesota) and from 1.3 (CI: 0.6-2.8) in year 2 to 4.0 (CI: 1.9-8.4) in year 6 (Oregon).
  
  
  CONCLUSIONS
  This evaluation reports steady increase in risk of pertussis in the years after completion of the 5-dose DTaP series. This rise is likely attributable in part to waning immunity from DTaP vaccines. Continuing to monitor disease burden and vaccine effectiveness in fully vaccinated children in coming years will be important to assess ongoing risk as additional cohorts vaccinated solely with acellular pertussis vaccines are introduced.
authors.affiliation: Centers for Disease Control and Prevention, Atlanta, Georgia, USA. sara.y.tartof@kp.org
authors.forename: Sara Y
authors.initials: SY
authors.lastname: Tartof
authors.forename: Melissa
authors.initials: M
authors.lastname: Lewis
authors.forename: Cynthia
authors.initials: C
authors.lastname: Kenyon
authors.forename: Karen
authors.initials: K
authors.lastname: White
authors.forename: Andrew
authors.initials: A
authors.lastname: Osborn
authors.forename: Juventila
authors.initials: J
authors.lastname: Liko
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Zell
authors.forename: Stacey
authors.initials: S
authors.lastname: Martin
authors.forename: Nancy E
authors.initials: NE
authors.lastname: Messonnier
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Clark
authors.forename: Tami H
authors.initials: TH
authors.lastname: Skoff
mesh_terms: D002648:Child; D002675:Child, Preschool; D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines / Q000008:administration & dosage / Q000276:immunology*; D005500:Follow-Up Studies; D006801:Humans; D007115:Immunization Schedule; D015994:Incidence; D007223:Infant; D008910:Minnesota / Q000453:epidemiology; D015233:Models, Statistical; D016017:Odds Ratio; D009922:Oregon / Q000453:epidemiology; D011159:Population Surveillance; D013997:Time Factors; D014917:Whooping Cough / Q000453:epidemiology / Q000276:immunology* / Q000517:prevention & control
chemical_list: D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines