PAHO highlights surge in yellow fever cases across the Americas in 2025

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

The cases are located 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).

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

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

While vaccination capacities in endemic countries have since improved, the limited global supply of yellow fever vaccine continues to pose a challenge, with current supplies unable to cover demand in the Americas and in Africa.

In the risk assessment, issued on 23 May, PAHO calls for the need to strengthen surveillance, vaccination of at-risk populations, and communication strategies to ensure the provision of public health advice for affected communities and those travelling 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 where appropriate and identifying populations most at risk and in greatest need of vaccination.

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

PAHO continues to monitor the situation and support countries in adopting the best strategies for preventing and responding to yellow fever outbreaks.