Sensitivity evaluation of a modified real-time reverse-transcription PCR primer to detect a measles virus variant in Japan in 2024.

A measles outbreak occurred in Japan in February 2024 due to a measles virus variant that was imported from central Asian countries with three mismatches at the PCR reverse primer (MVN1213R) annealing site. To examine and improve the impact of real-time PCR effectiveness for detecting this variant, we compared the sensitivity of real-time PCR between MVN1213R and a modified primer using control RNAs, clinical isolates, and clinical specimens. The median difference in the cycle threshold value was 2.92 (interquartile range, IQR 1.99-3.38) lower using the modified primer compared with MVN1213R. Thus, PCR primer sets should be modified to effectively detect this measles virus mutation.