Nationwide Multicenter Laboratory-Based Analysis of Varicella-Zoster Virus IgG and IgM Seropositivity in Korea, 2014-2024.

BACKGROUND: Varicella-zoster virus (VZV) remains an endemic, vaccine-preventable infection in Korea, despite high national vaccination coverage. Understanding long-term population immunity trends is essential for refining the disease-control and immunization policies. In this nationwide multicenter laboratory-based study, we evaluated 10-yr trends in VZV IgG and IgM seropositivity using large-scale data. METHODS: We retrospectively analyzed 580,344 VZV IgG and 228,258 IgM test results from eight institutions, including six university hospitals and two nationwide referral laboratories, from January 2014 to September 2024. Seropositivity trends were assessed according to age, sex, region, test year, institution, and assay reagents. RESULTS: Overall IgG seropositivity was 90.6%, whereas IgM seropositivity was 3.3%. IgG seropositivity was lowest in infants aged <1 yr (29.6%); this increased progressively with age, exceeding 96% in adults aged ≥ 40 yrs. Among children, the lowest seropositivity was observed in those aged 1-4 yrs (53.2%). After 2021, a temporal age shift in the childhood immunity gap occurred, with the lowest seropositivity shifting to children aged 5-9 yrs. IgM seropositivity was highest in early childhood, declined during the coronavirus disease 2019 pandemic, and rebounded thereafter. Regional IgG seropositivity ranged from 85.1% to 92.6%. IgG seropositivity also varied by assay reagent, ranging from 88.4% to 94.6%. CONCLUSIONS: This analysis demonstrated persistently high VZV IgG immunity in Korean adults but identified a persistent early childhood immunity gap with a recent age shift. Regional and assay-dependent variability highlights the need for standardized seroepidemiologic monitoring and can inform vaccination policy evaluation in Korea.