title: Impact of a pertussis epidemic on infant vaccination in Washington state.
abstract: OBJECTIVE
  Washington State experienced a pertussis epidemic from October 2011 to December 2012. There was wide variation in incidence by county. The objectives of this study were to determine how the pertussis epidemic affected infant vaccination in Washington State and whether the incidence in counties modified this effect.
  
  
  METHODS
  We conducted an ecologic before-after study to compare the proportion of infants up to date (UTD) with a pertussis-containing vaccine at time points before (September 30, 2011), during (September 30, 2012), and after (September 30, 2013) the epidemic. Children aged 3 to 8 months enrolled in the Washington State Immunization Information System with documented county of residence were included. UTD status was determined as ≥ 1, ≥ 2, or ≥ 3 doses of a pertussis-containing vaccine at ages 3, 5, and 7 months, respectively. Generalized linear models with extension to the binomial family and clustered robust standard errors were used to examine differences in the proportion of UTD infants between preepidemic and either epidemic or postepidemic points. The potential modifying effect of pertussis incidence by county was examined.
  
  
  RESULTS
  We found no significant difference in statewide UTD status with a pertussis-containing vaccine between preepidemic and either epidemic (absolute difference 2.1%; 95% confidence interval, -1.6 to 5.9) or postepidemic (absolute difference 0.2%; 95% confidence interval, -4.0 to 4.5) time points. There was no significant modification by county pertussis incidence. There was wide variation in the absolute difference in UTD status across counties.
  
  
  CONCLUSIONS
  A statewide pertussis epidemic does not appear to have significantly changed the proportion of infants who were UTD with a pertussis-containing vaccine.
authors.affiliation: Seattle Children's Research Institute, Seattle, Washington; Departments of Pediatrics, and ewolf@uw.edu.
authors.forename: Elizabeth R
authors.initials: ER
authors.lastname: Wolf
authors.affiliation: Seattle Children's Research Institute, Seattle, Washington; Departments of Pediatrics, and.
authors.forename: Douglas
authors.initials: D
authors.lastname: Opel
authors.affiliation: Washington State Department of Health, Olympia, Washington; and.
authors.forename: M Patricia
authors.initials: MP
authors.lastname: DeHart
authors.affiliation: Washington State Immunization Information System, Seattle, Washington.
authors.forename: Jodi
authors.initials: J
authors.lastname: Warren
authors.affiliation: Epidemiology, University of Washington, Seattle, Washington;
authors.forename: Ali
authors.initials: A
authors.lastname: Rowhani-Rahbar
mesh_terms: D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D015721:Diphtheria-Tetanus-Pertussis Vaccine / Q000008:administration & dosage*; D058872:Epidemics; D005260:Female; D006801:Humans; D007115:Immunization Schedule; D007223:Infant; D008297:Male; D010567:Pertussis Vaccine / Q000008:administration & dosage*; D014611:Vaccination / Q000639:trends*; D014861:Washington / Q000453:epidemiology; D014917:Whooping Cough / Q000175:diagnosis / Q000453:epidemiology* / Q000517:prevention & control*
chemical_list: D015721:Diphtheria-Tetanus-Pertussis Vaccine; D010567:Pertussis Vaccine
keywords: DTaP; epidemic; exemption; infant; media; outbreak; pertussis; vaccination; vaccines