Risk factors of herpes zoster among children immunized with varicella vaccine: results from a nested case-control study.

BACKGROUND: Previous studies of varicella-zoster virus reactivation in children have provided little information on potential risk factors. The aim of this study was to investigate the effects of race, chronic medical conditions and treatments, and recent vaccination, on the risk of herpes zoster (HZ) in children vaccinated with one dose of varicella vaccine.

METHODS: Case subjects were identified from a cohort of subjects who were members of the Southern California Kaiser Permanente Health Plan and received primary immunization with a single-antigen live varicella vaccine at age < or = 12 years from 2002 to 2008. Control subjects free of HZ during the study period were matched at a 5:1 ratio to each case subject on date of birth and sex. Race information was obtained from membership files, health records, and phone interview. Immunization history, medical history, and health care utilization were identified from Southern California Kaiser Permanente Health Plan electronic records.

RESULTS: During this time, 122 children were diagnosed with HZ. With adjustment for the number of hospitalizations, outpatient visits, and length of time between vaccination with varicella vaccine and the onset of HZ, Black children were at lower risk of developing HZ than were White (OR=0.41, 95% CI=0.17-0.98) and Asian children (OR=0.30, 95% CI=0.11-0.84).

CONCLUSIONS: These data suggest that the racial differences in the risk of developing HZ seen in adults are manifest in children as well. As children are not subject to the majority of factors hypothesized to underlie HZ in adults and as this study was conducted in a setting which affords equal access to health care, it is possible that genetic variation may explain some portion of varicella-zoster virus reactivation.