Yellow fever cases on the rise in the Americas

On May 23rd, the Pan American Health Organization (PAHO) released a new Rapid Risk Assessment (RRA) concerning yellow fever in the Americas. This assessment emphasizes a significant public health risk due to the increased incidence of cases within regional areas. The elevated incidence is related to the recurring reactivation of sylvatic transmission cycles involving human cases. In 2025, countries in the region collectively reported 221 confirmed human cases of yellow fever, including 89 fatalities. This represents an over eightfold increase in cases compared to the corresponding period in 2024. The majority of cases are concentrated in Bolivia (3 cases, 1 death), Brazil (110 cases, 44 deaths), Colombia (64 cases, 26 deaths), Ecuador (6 cases, 5 deaths) and Peru (38 cases, 13 deaths), extending beyond the Amazon region to areas such as the State of São Paulo in Brazil and the Department of Tolima in Colombia, thereby increasing the potential for urban outbreaks. Almost all cases reported in 2024 and 2025 occurred in unvaccinated individuals. According to health authorities, 10 of the 12 endemic countries currently have immunization coverage rates below the 95% threshold recommended by WHO, primarily due to an insufficient supply to meet the needs of the local population. The disease, characterized by hemorrhage, is endemic to tropical regions of the Americas and Africa. It presents in approximately 15% of cases with symptoms including elevated fever, organ dysfunction, and, in some instances, mortality.