title: Association of childhood pertussis with receipt of 5 doses of pertussis vaccine by time since last vaccine dose, California, 2010.
abstract: BACKGROUND
  In 2010, California experienced its largest pertussis epidemic in more than 60 years; a substantial burden of disease was noted in the 7- to 10-year-old age group despite high diphtheria, tetanus, and acellular pertussis vaccine (DTaP) coverage, indicating the possibility of waning protection.
  
  
  OBJECTIVE
  To evaluate the association between pertussis and receipt of 5 DTaP doses by time since fifth DTaP dose.
  
  
  METHODS
  Case-control evaluation conducted in 15 California counties. Cases (n = 682) were all suspected, probable, and confirmed pertussis cases among children aged 4 to 10 years reported from January through December 14, 2010; controls (n = 2016) were children in the same age group who received care from the clinicians reporting the cases. Three controls were selected per case. Vaccination histories were obtained from medical records and immunization registries.
  
  
  METHODS
  Primary outcomes were (1) odds ratios (ORs) for the association between pertussis and receipt of the 5-dose DTaP series and (2) ORs for the association between pertussis and time since completion (<12, 12-23, 24-35, 36-47, 48-59, or ≥60 months) of the 5-dose DTaP series. Logistic regression was used to calculate ORs, accounting for clustering by county and clinician, and vaccine effectiveness (VE) was estimated as (1 - OR) × 100%.
  
  
  RESULTS
  Among cases and controls, 53 (7.8%) and 19 (0.9%) had not received any pertussis-containing vaccines, respectively. Compared with controls, children with pertussis had a lower odds of having received all 5 doses of DTaP (OR, 0.11; 95% CI, 0.06-0.21 [estimated VE, 88.7%; 95% CI, 79.4%-93.8%]). When children were categorized by time since completion of the DTaP series, using an unvaccinated reference group, children with pertussis compared with controls were less likely to have received their fifth dose within the prior 12 months (19 [2.8%] vs 354 [17.6%], respectively; OR, 0.02; 95% CI, 0.01-0.04 [estimated VE, 98.1%; 95% CI, 96.1%-99.1%]). This association was evident with longer time since vaccination, with ORs increasing with time since the fifth dose. At 60 months or longer (n = 231 cases [33.9%] and n = 288 controls [14.3%]), the OR was 0.29 (95% CI, 0.15-0.54 [estimated VE, 71.2%; 95% CI, 45.8%-84.8%]). Accordingly, the estimated VE declined each year after receipt of the fifth dose of DTaP.
  
  
  CONCLUSIONS
  Among children in 15 California counties, children with pertussis, compared with controls, had lower odds of having received the 5-dose DTaP series; as time since last DTaP dose increased, the odds increased, which is consistent with a progressive decrease in estimated vaccine effectiveness each year after the final dose of pertussis vaccine.
authors.affiliation: Epidemic Intelligence Service and Meningitis and Vaccine Preventable Diseases Branch, Division of Bacterial Diseases, National Center for Immunization and Respiratory Diseases, US Centers for Disease Control and Prevention, 1600 Clifton Rd NE, MS-C25, Atlanta, GA 30329, USA. lmisegades@cdc.gov
authors.forename: Lara K
authors.initials: LK
authors.lastname: Misegades
authors.forename: Kathleen
authors.initials: K
authors.lastname: Winter
authors.forename: Kathleen
authors.initials: K
authors.lastname: Harriman
authors.forename: John
authors.initials: J
authors.lastname: Talarico
authors.forename: Nancy E
authors.initials: NE
authors.lastname: Messonnier
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Clark
authors.forename: Stacey W
authors.initials: SW
authors.lastname: Martin
mesh_terms: D002140:California / Q000453:epidemiology; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines / Q000008:administration & dosage* / Q000592:standards; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D007115:Immunization Schedule; D016015:Logistic Models; D008297:Male; D016017:Odds Ratio; D013997:Time Factors; D014917:Whooping Cough / Q000453:epidemiology* / Q000517:prevention & control*
chemical_list: D022681:Diphtheria-Tetanus-acellular Pertussis Vaccines