WASHINGTON, United States (CMC) — The Pan American Health Organization (PAHO) has issued a new Rapid Risk Assessment (RRA) on yellow fever in the Americas, including the Caribbean, which it said shows that the risk to public health remains high due to continued human cases in endemic countries of the region.

PAHO said that so far this year, there has been a more than eightfold increase in cases compared to the same period of 2024.

It said this is due to the periodic reactivation of sylvatic transmission cycles with spillover cases among people and that, in total, countries have reported 221 confirmed human cases of yellow fever, including 89 deaths.

In comparison, in 2024, there were 61 human cases confirmed, including 30 deaths.

PAHO said that 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 São Paulo State in Brazil and Tolima Department in Colombia.

It said 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. Before the COVID-19 pandemic, vaccination coverage against yellow fever in endemic countries of the region ranged from 57 per cent to 100 per cent among children aged nine to 18 months.

“However, 10 out of 12 endemic countries had coverage rates below the recommended 95 per cent. Between 2020-2023, these rates declined further, leaving a substantial proportion of the population unprotected,” PAHO said.

It said that 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, 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 said it is also working with endemic countries to provide technical support aimed at optimising 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 Haemagogus and Sabethes species.

Symptoms usually appear three to six 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 per cent experience high fever, organ damage and sometimes death.

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