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.

Background:
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.

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

Methods:
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)).

Results:
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).

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