Yellow fever - Global

WHO Disease Outbreak News

Published

24 Jun 2026

Yellow fever is a viral disease found in areas of Africa and the Americas, spread by infected mosquitoes. Following an increase of cases in the Americas in 2025, transmission activity remained into 2026. From 1 January to 26 May 2026, six countries reported a total of 79 human infections along with multiple epizootics, indicating active sylvatic circulation. In Africa, sustained activity continued across parts of the region, affecting 13 high-risk countries (as per classification in the Eliminate Yellow fever Epidemics (EYE) Strategy). From January to May 2026, three countries in Africa reported 16 confirmed human cases, with an additional 32 suspected cases under investigation in five other countries. The recent rapid risk assessment assessed geographical variations in vaccination coverage, evidence of viral circulation, and the presence of competent vectors, concluding that unvaccinated populations in countries or areas with a history of yellow fever transmission remain at greatest risk. Transmission dynamics are further influenced by seasonal ecological factors, particularly rainfall, temperature, and mosquito abundance. Outbreaks reported from October 2025 through May 2026 in countries or areas with a history of yellow fever transmission were generally consistent with seasonal patterns or reflected gaps in immunization coverage. In contrast, cases detected in previously unaffected areas suggest viral introduction and an increased risk of urban transmission. No imported cases were detected outside the two affected WHO regions, but expanding vector suitability, rapid urbanization, climate shifts, and increased mobility continue to create conditions conducive to international spread.WHO emphasizes the importance of active surveillance, timely laboratory testing, cross-border coordination, and information sharing. Vaccination remains the primary means for the prevention and control of yellow fever. WHO continues to support countries in expanding vaccination coverage through routine immunization programmes and preventive vaccination campaigns to enhance population immunity and reduce the risk of outbreaks.