Genomic study tracks massive chikungunya epidemic on Réunion Island

Summary

Réunion Island experienced a major chikungunya epidemic from August 2024 through June 2025, producing more than 54,000 confirmed cases and 43 deaths. Researchers sequenced over 3,000 viral genomes and used evolutionary, geographic, demographic, climate, and immunity data to reconstruct the outbreak. They concluded that a likely single introduction spread through extensive human movement between municipalities. Although climate influenced transmission, accumulated immunity—estimated at 66% of the population—appears to have driven the epidemic below sustained transmission levels. Few local cases followed, suggesting limited near-term resurgence risk.