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Risk assessment elaborated with the data available as of 30 January 2025
General Risk Statement
This rapid risk assessment (RRA) aims to assess the current public health risk associated with the increase of yellow fever cases in the last term of 2024 and the beginning of 2025 in endemic countries of the American Region.
This RRA has been conducted considering the following criteria: (i) the potential risk to human health (including exposure risk, clinical-epidemiological behavior of the disease, indicators of magnitude and severity, as well as more detailed risk factors and determinants), based on the increasing trend of confirmation of cases during 2024 and 2025, and the case fatality rate among cases (50%) during 2024; (ii) the risk of dissemination, particularly the potential spread to areas that historically have been classified as low risk for the disease, and (iii) the public health risk on varying capacities for early detection, prevention and control within endemic countries, low vaccine coverage, as well as challenges regarding a scenario of yellow fever vaccine shortage in the Region.
Yellow fever is an acute haemorrhagic disease that is endemic in twelve countries and one territory in South America: Argentina, the Plurinational State of Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Panama, Paraguay, Peru, Suriname, Trinidad and Tobago, and the Bolivarian Republic of Venezuela (1, 2). The disease has caused numerous epidemics with high mortality rates throughout history. Cases can be difficult to distinguish from other viral haemorrhagic fevers such as arenavirus, hantavirus or dengue. In context, where dengue outbreaks are evolving, the diagnosis of the disease, especially during the early stages, could be difficult, especially when healthcare workers lack experience in detecting and treating cases (1).
In 2024, 61 human cases of yellow fever were confirmed in the Americas Region, of which 30 were fatal (case fatality ratio, CFR= 50%), distributed among five countries (3). Between epidemiological week (EW) 1 and EW 4 of 2025, 16 confirmed human cases of yellow fever have been reported, of which seven have been fatal. In 2024, cases were mainly reported throughout the Amazon region of the Plurinational State of Bolivia, Brazil, Colombia, Guyana, and Peru. In 2025, cases have been recorded primarily in the State of Sao Paulo in Brazil and the Department of Tolima in Colombia, regions outside the Amazon region of these two countries (3). In the Americas, there are two yellow fever transmission cycles: sylvatic and urban. All cases occurred in persons who had a history of exposure in wild and/or forested areas (sylvatic cycle) due to work or ecotourism activities (1-3).
The risk of yellow fever outbreaks in the Americas Region is high. Most cases reported during 2024 did not have a history of yellow fever vaccination (3). Even though regional yellow fever vaccine coverage levels were not optimal before the COVID-19 pandemic, vaccination coverage declined significantly between 2020 and 2023, increasing the number of susceptible populations in all endemic countries. In 2023, Ecuador and Guyana achieved yellow fever vaccine coverage greater than or equal to 95%, and only two countries Suriname and Trinidad and Tobago had coverage between 90% and 94%. In addition, six countries had yellow fever vaccine coverage of less than 80%: Argentina, the Plurinational State of Bolivia, Brazil, Panama, Peru, and the Bolivarian Republic of Venezuela (4).
Although the Americas Region has strengthened the endemic countries surveillance, diagnosis, and vaccination capacities, the global supply of yellow fever vaccines has been showing fluctuation in the recent years, which can reduce the access of susceptible people to be vaccinated and lead to a lack of response to yellow fever outbreaks. As of early 2025, available yellow fever vaccine supply for the region is also severely constraint and is not sufficient to cover the routine regional demand for the year.
The increase in confirmed yellow fever cases in the Americas Region has highlighted the need to strengthen surveillance, vaccination of at-risk populations, and risk communication strategies for travelers going to areas where vaccination is recommended. The systematic exposure of yellow fever cases to sylvatic related activities stresses the need for approaches targeting individuals working in wild or forested areas, such as loggers, farmers, and ecotourism professionals. Best practices in clinical management, with emphasis on the detection and timely treatment of severe cases, must be disseminated to healthcare workers in endemic areas. In addition, countries should have vaccine stockpiles, depending on vaccine availability, to ensure a rapid response to possible outbreaks (3).
The overall risk of this event in the Americas Region, especially in endemic countries, is classified as ¨High¨ with a ¨High¨ level of confidence based on the available information.
The rapid risk assessment will be reviewed should further epidemiological, clinical, or virological information become available.