title: Encephalopathy after whole-cell pertussis or measles vaccination: lack of evidence for a causal association in a retrospective case-control study.
abstract: BACKGROUND
  Whole-cell pertussis (wP) and measles vaccines are effective in preventing disease but have also been suspected of increasing the risk of encephalopathy or encephalitis. Although many countries now use acellular pertussis vaccines, wP vaccine is still widely used in the developing world. It is therefore important to evaluate whether wP vaccine increases the risk of neurologic disorders.
  
  
  METHODS
  A retrospective case-control study was performed at 4 health maintenance organizations. Records from January 1, 1981, through December 31, 1995, were examined to identify children aged 0 to 6 years old hospitalized with encephalopathy or related conditions. The cause of the encephalopathy was categorized as known, unknown or suspected but unconfirmed. Up to 3 controls were matched to each case. Conditional logistic regression was used to analyze the relative risk of encephalopathy after vaccination with diphtheria-tetanus-pertussis (DTP) or measles-mumps-rubella (MMR) vaccines in the 90 days before disease onset as defined by chart review compared with an equivalent period among controls indexed by matching on case onset date.
  
  
  RESULTS
  Four-hundred fifty-two cases were identified. Cases were no more likely than controls to have received either vaccine during the 90 days before disease onset. When encephalopathies of known etiology were excluded, the odds ratio for case children having received DTP within 7 days before onset of disease was 1.22 (95% confidence interval [CI] = 0.45-3.31, P = 0.693) compared with control children. For MMR in the 90 days before onset of encephalopathy, the odds ratio was 1.23 (95% confidence interval = 0.51-2.98, P = 0.647).
  
  
  CONCLUSIONS
  In this study of more than 2 million children, DTP and MMR vaccines were not associated with an increased risk of encephalopathy after vaccination.
authors.affiliation: Kaiser Permanente Vaccine Study Center, Oakland, CA 94612, USA.
authors.forename: Paula
authors.initials: P
authors.lastname: Ray
authors.forename: Jean
authors.initials: J
authors.lastname: Hayward
authors.forename: David
authors.initials: D
authors.lastname: Michelson
authors.forename: Edwin
authors.initials: E
authors.lastname: Lewis
authors.forename: Joan
authors.initials: J
authors.lastname: Schwalbe
authors.forename: Steve
authors.initials: S
authors.lastname: Black
authors.forename: Henry
authors.initials: H
authors.lastname: Shinefield
authors.forename: Michael
authors.initials: M
authors.lastname: Marcy
authors.forename: Ken
authors.initials: K
authors.lastname: Huff
authors.forename: Joel
authors.initials: J
authors.lastname: Ward
authors.forename: John
authors.initials: J
authors.lastname: Mullooly
authors.forename: Robert
authors.initials: R
authors.lastname: Chen
authors.forename: Robert
authors.initials: R
authors.lastname: Davis
mesh_terms: D001927:Brain Diseases / Q000209:etiology*; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D015721:Diphtheria-Tetanus-Pertussis Vaccine / Q000009:adverse effects*; D004660:Encephalitis / Q000209:etiology; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D022542:Measles-Mumps-Rubella Vaccine / Q000009:adverse effects*; D012189:Retrospective Studies
chemical_list: D015721:Diphtheria-Tetanus-Pertussis Vaccine; D022542:Measles-Mumps-Rubella Vaccine