In South Korea, the one-dose varicella vaccine was added to the National Immunization Program for children aged 12–15 months in 2005, and vaccination coverage reached more than 95%. The effect of varicella vaccine on varicella and herpes zoster (HZ) was studied while taking demographic changes into consideration. We used the National Health Information Database to compute the crude and age-sex standardized incidence rates (IRs) and age-specific IRs of varicella and HZ from 2003 to 2015. The yearly incidence rate ratios (IRRs) were computed using a negative binomial regression analysis that took age and gender into account. The crude varicella IR fell by 67 percent, from 5.70/1000 to 1.87/1000 person years, while the adjusted IRs fell significantly only from 2010 to 2015. The biggest reduction was seen in children aged 4 years, but the IR rose until 2011 and subsequently declined in children aged 5–9 years, who had the highest incidence age group in 2013–2015. The crude HZ IR rose from 2.67/1000 to 9.80/1000 person years, and the adjusted IR followed suit. Before and after universal immunization, a similar rising tendency was found.

Although one-dose varicella vaccine was somewhat successful in preventing varicella, it was insufficient to stop varicella transmission in children. Furthermore, the incidence of HZ has grown substantially during the last decade. The present varicella-zoster immunization approach should be reviewed.