The impact of a varicella vaccine introduction on the incidence of herpes zoster in Korean children, an ecological study

SKYVaricellaTM, a live attenuated varicella vaccine product, is known to increase the risk of herpes zoster (HZ) in vaccinated children. We investigated the impact of introducing the vaccine on HZ incidence in Korea since 2018. This ecological study used medical records from the Health Insurance Review and Assessment Service in Korea. We present data on HZ incidence trend in children (<10 years) from 2010 to 2024. A change in HZ incidence trend was evaluated using linear regression analysis, with vaccine introduction as an interaction term. We then calculated the number of excess HZ cases due to the vaccine introduction in Korea. HZ incidence in children <10 years presented a downward trend that continuously declined from 2010 to 2018. This downward trend was reversed to an upward trend in children <5 years, whereas the decreasing trend in children aged 5-9 years continued after 2019. The change in trend in children <5 years in 2019 was statistically significant (p < 0.001). There were 6,484 excess HZ cases in children <5 years from January 2019 to June 2024. The vaccine introduction has resulted in a large-scale ongoing HZ outbreak in children in Korea. More studies are needed to assess the long-term impact of the vaccine on HZ incidence in vaccinated individuals.