Laboratory-based Surveillance to Sustain Measles Elimination in the Republic of Korea.

Objectives: To describe the operation of a laboratory-based measles surveillance system required to sustain measles elimination and to provide directions to reinforce molecular surveillance. Methods: The study used a case-based surveillance system linked to the mandatory reporting of suspected measles cases. It employed measles-specific antibody testing and real-time reverse transcription polymerase chain reaction for laboratory confirmation, enabling differentiation between wild-type and vaccine-associated cases. Positive specimens were subjected to N450 and non-coding region located between the Matrix and Fusion protein genes (MF-NCR) sequencing, and the obtained sequence data were submitted to the World Health Organization. Regular proficiency testing and training support laboratory capacity. Results: A total of 2,377 measles diagnostic tests were performed between 2021 and 2025. Of these specimens, 1,267 cases were tested in 2025, an increase of 130.4% from 2024. Genotyping was completed for 130 of the 135 confirmed cases, and genotypes B3 (74.6%) and D8 (25.4%) were identified. Genotype H1, which is historically endemic in the Republic of Korea (ROK), was not detected. Conclusions: National laboratory-based surveillance supports the sustained elimination of measles by integrating diagnostic and molecular confirmation. However, the resolution of N450 and Sanger sequencing-based analysis is limited by reduced genotype diversity and sequence variation in the MF-NCR. Laboratory capacity must be maintained, and high-resolution MF-NCR analysis using NGS must be performed to sustain ROK's current measles elimination status.