Reemergence of Yellow Fever, Magdalena Valley, Colombia, 2024–2025

Yellow fever, a zoonotic arboviral disease, has reemerged in Colombia, triggering a major outbreak in the country. During 2024 through mid-2025, a total of 132 human cases and 68 infections in nonhuman primates were confirmed, primarily in the department of Tolima, historically considered a low-risk area. We analyzed the historical and current epidemiology of yellow fever in Colombia, highlighting ecologic, social, and surveillance factors that contributed to the outbreak. Low vaccination coverage, insufficient epizootic and entomological surveillance, deforestation, habitat fragmentation, and limited application of One Health approaches have all exacerbated the situation. The high mortality rate of nonhuman primate species indicated a more profound ecologic crisis. Immediate, comprehensive measures, including mass vaccination, genomic surveillance, and integrated One Health frameworks, are urgently needed. Colombia's experience underscores the need to reevaluate risk stratification and preparedness strategies across the Americas to prevent future yellow fever outbreaks in previously unaffected regions.