To exploit these data, the team of Belgian, French and American researchers applied phylodynamic and phylogeographic approaches (statistical methods that read the evolutionary relationships between viral genomes to reconstruct where and how a pathogen has travelled). The analyses indicate that the epidemic likely stemmed from a single introduction and that the virus then circulated in a highly intermixed fashion, with frequent movements between municipalities, driven by human mobility and population density. This human-driven spread was especially visible at the peak of the epidemic, with repeated viral exchanges between distant residential areas.

The researchers also examined the factors explaining why the epidemic ended. Their models show that the epidemic's dynamics were associated with climatic conditions (temperature and precipitation, which shape mosquito density and activity), but that climate alone cannot account for the decline in transmission. The gradual build-up of population immunity was, in theory, sufficient to push - on its own - the effective reproduction number below 1, bringing the outbreak to an end. With an estimated 66% of the population now immune to the virus, the authors conclude that the risk of a large resurgence is low. This prediction was borne out by the following season, during which only a handful of local cases were reported despite continued chikungunya virus circulation elsewhere in the Indian Ocean.

Source:

Journal reference:

Frumence, E., et al. (2026). Unraveling the epidemiological and dispersal dynamics of the 2024–2025 chikungunya virus epidemic on Réunion Island. Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.2621019123. https://www.pnas.org/doi/10.1073/pnas.2621019123