Climate variability is associated with chikungunya outbreaks across the Indian Ocean Region

In 2025, chikungunya resurged across the Indian Ocean Region (IOR), with climate-driven increases in temperature and rainfall influencing vector ecology and transmission. To assess the influence of large-scale climate forcing on CHIKV transmission dynamics, we employed a comprehensive set of climate indices representing the dominant modes of climate variability that shape monsoon dynamics and modulate regional weather across the IOR. Using GeoSentinel traveler surveillance data from 2010 to 2024, which closely mirrors global chikungunya epidemiological trends, we examined associations between these climate indices and acute chikungunya cases acquired in the IOR. Chikungunya activity showed region-specific associations with the Mascarene Subtropical High (MSH): In South-Central Asia, outbreaks were strongly correlated with intensified MSH area during El Niño; in Sub-Saharan Africa, the relationship was weaker and spatially heterogeneous, suggesting that other climatic drivers, such as Indian summer monsoon onset and cross-equatorial flow may play a more dominant role; in Southeast Asia, elevated chikungunya activity typically followed moderate-to-large eastward expansions of the MSH, often with a temporal lag, consistent with a delayed positive association and frequently linked to anomalous westerly flow into the Maritime Continent. Improved understanding of these climate–disease linkages could strengthen early warning systems and support more targeted public health interventions to mitigate future chikungunya outbreaks.