title: Unchanged efficacy of a pertussis toxoid vaccine throughout the two years after the third vaccination of infants.
abstract: BACKGROUND
  In a previously reported double blind efficacy trial of a pertussis toxoid vaccine, 3450 infants were randomized to receive diphtheria-tetanus toxoids with or without pertussis toxoid at 3, 5 and 12 months of age. Efficacy against pertussis as defined by the World Health Organization was 71% from 30 days after the third vaccination with an average follow-up of 17.5 months. We now report efficacy for an additional 6 months of open follow-up.
  
  
  METHODS
  Parents were contacted monthly by a nurse. If a participant or a family member coughed for > or = 7 days, a nasopharyngeal sample and paired sera were obtained.
  
  
  RESULTS
  Efficacy during this open follow-up period was 77% (95% confidence intervals, 66 to 85%) based on 29 and 110 cases fulfilling the WHO definition of pertussis in vaccinated and control children, respectively. Efficacy against household exposure was 76% (95% confidence intervals, 51 to 91%). Pertussis in vaccinated children had a significantly shorter duration than pertussis in control children. Determination of pertussis toxin antibodies in paired sera with enzyme-linked immunosorbent assay had a lower diagnostic sensitivity in vaccinated (45%) than in control (92%) children, while determination of antibodies against filamentous hemagglutinin (not included in the vaccine) was highly sensitive for diagnosing pertussis in both groups (100 and 90%, respectively).
  
  
  CONCLUSIONS
  A monocomponent pertussis toxoid vaccine induces significant protection against pertussis for at least 2 years after the third injection. To obtain an unbiased estimate of vaccine efficacy it is important to determine antibodies against an antigen that is not included in the vaccine.
authors.affiliation: Department of Pediatrics, Göteborg University, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Taranger
authors.forename: B
authors.initials: B
authors.lastname: Trollfors
authors.forename: T
authors.initials: T
authors.lastname: Lagergård
authors.forename: L
authors.initials: L
authors.lastname: Lind
authors.forename: V
authors.initials: V
authors.lastname: Sundh
authors.forename: G
authors.initials: G
authors.lastname: Zackrisson
authors.forename: D A
authors.initials: DA
authors.lastname: Bryla
authors.forename: J B
authors.initials: JB
authors.lastname: Robbins
mesh_terms: D000907:Antibodies, Bacterial / Q000096:biosynthesis*; D001886:Bordetella pertussis / Q000276:immunology* / Q000302:isolation & purification; D002675:Child, Preschool; D015331:Cohort Studies; D004168:Diphtheria Toxoid / Q000008:administration & dosage / Q000276:immunology; D022422:Diphtheria-Tetanus Vaccine; D015721:Diphtheria-Tetanus-Pertussis Vaccine / Q000008:administration & dosage / Q000276:immunology*; D005500:Follow-Up Studies; D006801:Humans; D007115:Immunization Schedule; D007223:Infant; D009305:Nasopharynx / Q000382:microbiology; D016133:Polymerase Chain Reaction; D016032:Randomized Controlled Trials as Topic; D013745:Tetanus Toxoid / Q000008:administration & dosage / Q000276:immunology; D014121:Toxoids / Q000276:immunology*; D014611:Vaccination; D017778:Vaccines, Combined / Q000008:administration & dosage / Q000276:immunology
chemical_list: D000907:Antibodies, Bacterial; D004168:Diphtheria Toxoid; D022422:Diphtheria-Tetanus Vaccine; D015721:Diphtheria-Tetanus-Pertussis Vaccine; D013745:Tetanus Toxoid; D014121:Toxoids; D017778:Vaccines, Combined; C051093:pertussis toxoid