title: Varicella vaccination and ischemic stroke in children: is there an association?
abstract: BACKGROUND
  Ischemic stroke is a known complication of varicella disease. Although there have been case reports of ischemic stroke after varicella vaccination, the existence and magnitude of any vaccine-associated risk has not been determined. OBJECTIVE. The purpose of this work was to determine whether varicella vaccination is associated with an increased risk of ischemic stroke and encephalitis in children within 12 months after vaccination.
  
  
  METHODS
  We conducted a retrospective cohort study based on computerized data from children 11 months through 17 years old enrolled for > or =12 months in the Vaccine Safety DataLink from 1991 through 2004. International Classification of Disease codes identified cases of ischemic stroke (433-436, 437.1, 437.4, 437.6, 437.8-437.9) and encephalitis (052.0, 323.5, 323.8-9). Cox regression was used to model the risk in the 12 months after vaccination relative to all other person-time. Covariates included calendar time, gender, and stroke risk factors (eg, sickle cell disease).
  
  
  RESULTS
  Varicella vaccine was administered to 35.3% of the 3.2 million children in the cohort. There were 203 new inpatient ischemic stroke diagnoses, including 8 that occurred within 12 months after vaccination; there was no temporal clustering. The adjusted stroke hazard ratio was not elevated during any of the time periods in the 12 months after vaccination. Stroke was strongly associated with known risk factors such as sickle cell disease and cardiac disease. None of the 243 encephalitis cases occurred during the first 30 days after vaccination, and there was no association between encephalitis and varicella vaccination at any time in the 12 months after vaccination.
  
  
  CONCLUSIONS
  Our retrospective cohort study of >3 million children found no association between varicella vaccine and ischemic stroke.
authors.affiliation: Marshfield Clinic Research Foundation, Epidemiology Research Center, ML-2, 1000 N Oak Ave, Marshfield, WI 54449, USA. donahue.james@mcrf.mfldclin.edu
authors.forename: James G
authors.initials: JG
authors.lastname: Donahue
authors.forename: Burney A
authors.initials: BA
authors.lastname: Kieke
authors.forename: W Katherine
authors.initials: WK
authors.lastname: Yih
authors.forename: Nicholas R
authors.initials: NR
authors.lastname: Berger
authors.forename: Jeremy S
authors.initials: JS
authors.lastname: McCauley
authors.forename: James
authors.initials: J
authors.lastname: Baggs
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Zangwill
authors.forename: Roger
authors.initials: R
authors.lastname: Baxter
authors.forename: Eileen M
authors.initials: EM
authors.lastname: Eriksen
authors.forename: Jason M
authors.initials: JM
authors.lastname: Glanz
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Hambidge
authors.forename: Nicola P
authors.initials: NP
authors.lastname: Klein
authors.forename: Edwin M
authors.initials: EM
authors.lastname: Lewis
authors.forename: S Michael
authors.initials: SM
authors.lastname: Marcy
authors.forename: Allison L
authors.initials: AL
authors.lastname: Naleway
authors.forename: James D
authors.initials: JD
authors.lastname: Nordin
authors.forename: Paula
authors.initials: P
authors.lastname: Ray
authors.forename: Edward A
authors.initials: EA
authors.lastname: Belongia
mesh_terms: D000293:Adolescent; D002545:Brain Ischemia / Q000139:chemically induced*; D019433:Chickenpox Vaccine / Q000009:adverse effects*; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D012189:Retrospective Studies; D020521:Stroke / Q000139:chemically induced*
chemical_list: D019433:Chickenpox Vaccine