Tuesday, March 18, 2008

Stroke is not Associated with Varicella Vaccination in Children

James G. Donahue1, Burney Kieke1, W. Katherine Yih2, Nick R. Berger1, Jeremy S. McCauley1, Stephanie A. Irving1, Edward A. Belongia1, and The Vaccine Safety Datalink Team. (1) Epidemiology Research Center, Marshfield Clinic Research Foundation, 1000 North Oak Avenue, ML2, Marshfield, WI, USA, (2) Department of Ambulatory Care and Prevention, Harvard Pilgrim Health Care, 133 Brookline Ave., 6th floor, Boston, MA, USA

Learning Objectives for this Presentation:
By the end of the presentation participants will able to describe the relationship between varicella vaccination and stroke among children.

Stroke is a known complication of varicella disease. Although there have been case reports of stroke after varicella vaccination, the magnitude of risk in vaccine recipients has not been defined.

Determine if varicella vaccination is associated with an increased risk of stroke and encephalitis in children within 12 months post-vaccination.

Retrospective cohort study based on automated data from children 1-17 years old enrolled for ≥12 months in the Vaccine Safety Datalink from 1991 through 2004. ICD codes identified inpatient cases of stroke (433-436, 437.1, 437.4, 437.6, 437.8-9) and encephalitis (052.0, 323.5, 323.8-9). Cox regression was used to model the risk in the 12 months post-vaccination relative to all other person-time. Covariates included calendar time, sex, and stroke risk factors (e.g., sickle-cell disease (SCD)).

Varicella vaccine was administered to 35.3% of the 3.2 million children in the cohort. There were 203 new stroke diagnoses, including 8 that occurred within 12 months post-vaccination; there was no temporal clustering. The adjusted stroke hazard ratio (HR) was not elevated in any time periods in the 12 months post-vaccination. The HR was 1.1 (95% CI 0.2-5.5) and 0.8 (95% CI 0.2-3.8) in the first 30 and 90 days post-vaccination, respectively. Stroke was strongly associated with known risk factors, such as SCD (HR=170.5, 95% CI 87-335) and cardiac disease (HR=19.9, 95% CI 11-35). There were no stroke cases in the 12 months after any of 59,910 documented diagnoses of varicella disease. There was no association between encephalitis and varicella vaccination (HR=0.4, 95% CI 0.1-2.4, 1st 90 days).

The results of this study do not support an association between varicella vaccination and subsequent diagnosis of stroke or encephalitis.