Herpes zoster and exposure to the varicella zoster virus in an era of varicella vaccination.

OBJECTIVES: We performed a case-control study to determine if participants with herpes zoster had fewer contacts with persons with varicella or zoster, and with young children, to explore the hypothesis that exposure to persons with varicella zoster virus (VZV) results in "immune boosting." METHODS: Participants were patients of the multispecialty Marshfield Clinic in Wisconsin. We identified patients aged 40 to 79 years with a new diagnosis of zoster from August 2000 to July 2005. We frequency matched control participants to case participants for age. We confirmed diagnoses by chart review and assessed exposures by interview. RESULTS: Interviews were completed by 633 of 902 eligible case participants (70.2%) and 655 of 1149 control participants (57.0%). The number of varicella contacts was not associated with zoster; there was no trend even at the highest exposure level (3 or more contacts). Similarly, there was no association with exposure to persons with zoster or to children, or with workplace exposures. CONCLUSIONS: Although exposure to VZV in our study was relatively low, the absence of a relationship with zoster reflects the uncertain influence of varicella circulation on zoster epidemiology.

Varicella vaccination and ischemic stroke in children: is there an association?

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. PATIENTS AND 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. CONCLUSION: Our retrospective cohort study of >3 million children found no association between varicella vaccine and ischemic stroke.