title: Immunization uptake in younger siblings of children with autism spectrum disorder.
abstract: BACKGROUND
  Parental concerns persist that immunization increases the risk of autism spectrum disorder, resulting in the potential for reduced uptake by parents of younger siblings of children with autism spectrum disorder ("younger sibs").
  
  
  OBJECTIVE
  To compare immunization uptake by parents for their younger child relative to their older child with autism spectrum disorder ("proband") and controls.
  
  
  METHODS
  Immunization status was obtained for 98 "younger sibs," 98 "probands," and 65 controls.
  
  
  RESULTS
  A significant group difference emerged for overall immunization status (Fisher's exact test = 62.70, p < .001). One or more immunizations in 59/98 younger sibs were delayed (47/98; 48%) or declined (12/98; 12.2%); immunizations were delayed in 16/98 probands (16.3%) and declined in only one. All controls were fully immunized, with only 6 (9.2%) delayed. Within the "younger sibs" group, 25/98 received an autism spectrum disorder diagnosis; 7 of whom (28%) were fully immunized. The rates of autism spectrum disorder diagnosis did not differ between immunized and nonimmunized younger sib groups, although small sample size limits interpretability of this result.
  
  
  CONCLUSIONS
  Parents who already have one child with autism spectrum disorder may delay or decline immunization for their younger children, potentially placing them at increased risk of preventable infectious diseases.
authors.affiliation: 1University of Toronto, Canada.
authors.forename: Ghassan
authors.initials: G
authors.lastname: Abu Kuwaik
authors.forename: Wendy
authors.initials: W
authors.lastname: Roberts
authors.forename: Lonnie
authors.initials: L
authors.lastname: Zwaigenbaum
authors.forename: Susan
authors.initials: S
authors.lastname: Bryson
authors.forename: Isabel M
authors.initials: IM
authors.lastname: Smith
authors.forename: Peter
authors.initials: P
authors.lastname: Szatmari
authors.forename: Bonnie M
authors.initials: BM
authors.lastname: Modi
authors.forename: Nadia
authors.initials: N
authors.lastname: Tanel
authors.forename: Jessica
authors.initials: J
authors.lastname: Brian
mesh_terms: D000328:Adult; D001722:Birth Order; D002170:Canada; D016022:Case-Control Studies; D002648:Child; D002659:Child Development Disorders, Pervasive; D002675:Child, Preschool; D015721:Diphtheria-Tetanus-Pertussis Vaccine / Q000627:therapeutic use; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D022542:Measles-Mumps-Rubella Vaccine / Q000627:therapeutic use; D010290:Parents; D023321:Poliovirus Vaccines / Q000627:therapeutic use; D011446:Prospective Studies; D035781:Siblings; D016312:Treatment Refusal / Q000706:statistics & numerical data*; D014611:Vaccination / Q000706:statistics & numerical data*
chemical_list: D015721:Diphtheria-Tetanus-Pertussis Vaccine; D022542:Measles-Mumps-Rubella Vaccine; D023321:Poliovirus Vaccines