A Retrospective Multicenter Study of Measles Seropositivity in Korea from 2014 to 2024

Background: Measles is a highly contagious viral disease requiring high herd immunity.Although the Republic of Korea has maintained measles elimination through national immunization programs, sporadic cases continue to occur.We evaluated age-and period-specific measles immunity levels using laboratory-based measles antibody data from Korea.Methods: In this retrospective multicenter seroepidemiological study, measles IgG and IgM test results obtained at eight medical institutions in Korea between January 2014 and September 2024 were analyzed.Seropositivity was analyzed by year, age group, sex, and region.Associations between demographic factors and antibody positivity were assessed using Poisson regression, and differences across assay platforms were analyzed using negative binomial regression.Results: A total of 383,441 measles IgG and 36,879 IgM tests were included.IgG seropositivity was 56.9-68.2%during 2014-2018, increased to 87.8% in 2019, and remained high at 87.2-88.2%during 2020-2024.The proportion of equivocal IgG results decreased from 14.2-17.9%during 2014-2018 to 3.0% in 2019 and remained low thereafter.IgM seropositivity was 2.5-7.2%during 2014-2018, decreased to 1.3% in 2019, and remained low at 0.5-1.0%during 2020-2024.The proportion of equivocal IgM results also declined over time.IgG seropositivity was lower among children and adolescents and highest among adults aged 50-69 years, whereas IgM seropositivity was relatively higher in younger age groups.Regional and assay platform-related differences were observed.Conclusions: Measles seropositivity patterns in Korea showed heterogeneity by age, region, and assay platform.Standardized interpretation considering assay characteristics may improve post-elimination measles surveillance.