Epidemiology of pediatric herpes zoster after varicella infection: a population-based study.

BACKGROUND There are limited population-based data regarding pediatric herpes zoster (HZ). METHODS Children aged <12 years with varicella infections between 2000 and 2006 were identified from a national population-based database and followed-up for a diagnosis of HZ until December 2008. Since a routine varicella vaccination program was started in 2004, vaccinated children without medically attended varicella were identified between 2004 and 2006, and followed-up for a diagnosis of HZ until December 2008. RESULTS Of 27 517 children with medically attended varicella, 428 developed HZ. The incidence of HZ was 262.1 per 100 000 person-years. Of 25 132 vaccinated children without medically attended varicella, 106 developed HZ. The incidence of HZ was 93.3 per 100 000 person-years. The mean duration from varicella to HZ was 4.12 years. Children diagnosed with varicella at aged <2 years had a higher incidence (P < .001) and shorter duration (P = .04) than those diagnosed aged ≧2 years. Children diagnosed with varicella aged ≥2 but <8 years had a significantly increased incidence of HZ after than before the vaccination program (relative risk = 1.85 at 3 years of follow-up, P = .03). Children with varicella infections had a significantly greater risk of HZ than vaccinated children without a history of varicella (relative risk = 2.31 at 4 years of follow-up, P < .001). CONCLUSIONS This study demonstrates the population-based epidemiologic characteristics of pediatric HZ among those who contracted varicella. In the early postvaricella vaccination period, an increased HZ incidence was observed among children with varicella infection aged ≥2 years.