Incidence of herpes zoster among children vaccinated with varicella vaccine in a prepaid health care plan in the United States, 2002-2008.

BACKGROUND: Herpes zoster (HZ), or shingles, is caused by reactivation of latent varicella-zoster virus after a primary infection with either wild-type or vaccine-type varicella-zoster virus, the latter having been introduced in 1995 for children. Since then, few population-based data about the incidence of childhood HZ are available.
METHODS: We identified children aged < or = 12 years who were vaccinated with 1 dose of varicella vaccine between 2002 and 2008 in a prepaid health plan and followed them through their electronic health records for a diagnosis of HZ. The medical records of these children were reviewed. Persistent and chronic conditions for these children before HZ were identified.
RESULTS: There were 172,163 children vaccinated, with overall follow-up of 446,027 person-years (Incidence rate = 27.4 per 100,000 person-years, 95% confidence interval: 22.7-32.7). Children vaccinated after age 5 years had a higher but not statistically significant different rate than children vaccinated between 12 and 18 months (34.3 vs. 28.5 per 100,000 person-years). Among children vaccinated between 12 and 18 months, incidence rates gradually increased each year in the first 4 years after vaccination (P < 0.001). Among the HZ cases, there were 1 (0.7%) case of lymphoid leukemia, 1 (0.7%) case of drug abuse, 16 (11.1%) cases of asthma with 3 or more acute exacerbations, 12 (8.3%) cases of developmental disorders, and 3 (2.1%) cases of psychological or mental disorders.
CONCLUSIONS: These data demonstrate that diagnosed HZ is rare among children following varicella vaccine. Despite the small numbers, the roles of delayed vaccination, severe asthma, and development disorders warrant further investigation. In the future, analyses of HZ isolates will be needed to identify the virus strains causing reactivation.