Circulation of Measles Virus Genotype B3 in the Republic of the Congo Between 2023 and 2024: A Molecular Characterization Study

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Background and Aims: The only previous sequence report of measles virus from the Republic of the Congo (RoC) dates back to samples collected in 2000. To update the molecular epidemiology of measles virus in the RoC, our study genotyped measles virus strains circulating in the country from January 2023 to May 2024. Methods: A total of 584 serum or plasma samples were collected by the National Laboratory of Public Health through its nationwide measles surveillance activities. Among these 584 suspected cases, 231 were IgM seropositive, and 170 of them were selected for molecular detection based on their collection date. Results: Of these, 20 cases were RT-qPCR positive, and six sequences were suitable for sequence analysis. Phylogenetic analysis confirmed that the detected measles virus belongs to genotype B3, which is one of the two genotypes currently circulating globally, alongside genotype D8. Genetic comparison revealed three closely related variants, suggesting either ongoing endemic transmission or potential importation. Notably, 45% of PCR-positive samples had received two vaccine doses, highlighting the need for robust vaccine efficacy evaluation. Conclusion: This study emphasizes the critical role of measles virus surveillance, genotyping capacities, and genetic characterization to strengthen regional disease monitoring and containment strategies.

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