Serological Susceptibility to Measles Among International Students in South Korea After a Cluster of Cases: A Cross-Sectional Study.

BACKGROUND

Even though South Korea had eliminated measles in 2006, a localized cluster of measles occurred in a university dormitory in Gyeongsangbuk-do, South Korea, in 2024, involving 22 international students. This study aims to explore measles transmission and to inform future preventive measures.

METHODS

In a cross-sectional study, 299 international students from two local universities underwent a self-reported questionnaire survey and targeted serological testing by enzyme-linked immunosorbent assay two months after the cluster of measles cases. Statistical analysis used Pearson's chi-square test, Fisher's exact test, multivariate logistic regression, and Firth's penalized logistic regression.

RESULTS

The overall seropositivity was 79.6%, and 78.0% among participants aged ≤30 years. Among multivariate analyses, nationality was independently associated with seropositivity (aOR up to 8.35 for Chinese students).

CONCLUSIONS

These findings underscore the immunity gaps among international students, with seropositivity remaining below the 95% threshold required for herd immunity. Targeted serological screening and catch-up vaccination may help to improve immunity in mobile populations.