Public health risk of yellow fever remains high in the Americas due to continued occurrence of human cases – PAHO/WHO

Washington DC May 27, 2025 – The Pan American Health Organization (PAHO) has issued a new rapid risk assessment (RRA) on yellow fever in the Americas, which shows that the risk to public health remains high due to continuous human cases in the endemic countries of the region.

In 2025 so far, there has been an increase of more than eight times in cases compared to the same 2024 period. This is due to the periodic reactivation of silvatic transmission cycles with cases of overflow among people. In total, countries have reported 221 confirmed human cases of yellow fever, including 89 deaths. In comparison, in all 2024, 61 human cases were confirmed, including 30 deaths.

The cases are found 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).

The concern is the fact that, although in 2024 most cases were reported in the Amazon region of Bolivia, Brazil, Colombia, Guyana and Peru, this year there have also been reported cases outside the Amazon region in areas such as the state of Sao Paulo in Brazil (similar to the 2016-2018 outbreak) and the department of Tolima in Colombia. The occurrence of silvatic yellow fever near densely populated areas increases the risk of urban outbreak.

Almost all cases reported both in 2024 and 2025 have occurred in unvaccinated individuals. Before the COVID-19 pandemic, the vaccination coverage against yellow fever in endemic countries of the region ranged between 57% and 100% among children from 9 to 18 months. However, 10 of the 12 endemic countries had coverage rates below the recommended 95%. Between 2020-2023, these rates decreased even more, leaving a substantial proportion of the unprotected population.

Although vaccination capabilities in endemic countries have since improved the limited global supply of the yellow fever vaccine continues to raise a challenge, and current supplies cannot cover demand in the Americas and Africa.

In the risk assessment, issued on May 23, the PAHO demands the need to strengthen surveillance, vaccination of populations at risk and communication strategies to guarantee the provision of public health advice for affected communities and those traveling to areas where vaccination is recommended.

Paho is also working with endemic countries to provide technical support aimed at optimizing vaccination strategies. This includes the use of fractional doses when they correspond to the most identification populations at risk and in the greatest need for vaccination.

Yellow fever is an acute hemorrhagic disease that is endemic in the tropical areas of the Americas and Africa. In the Americas, it is commonly transmitted by silvatic mosquitoes belonging to the species of Haemogogus and Sabethes. The symptoms usually appear 3-6 days after the sting of an infected mosquito and include fever, muscle pain, headache, chills, loss of appetite, nausea and vomiting. While most patient symptoms disappear, about 15% experience high fever, organ damage and sometimes death.

Paho continues to monitor the situation and support for countries in adopting the best strategies to prevent and respond to yellow fever outbreaks.