Yellow Fever Outbreak in the Americas

Introduction

Washington, D.C., (PAHO) – The Pan American Health Organization has issued a new epidemiological alert in response to an increase in yellow fever cases across the Americas during the first months of 2025. The number of confirmed human cases as of March 22 has more than doubled compared to the total recorded in all of 2024, raising concerns about a potential expansion of the disease.

Current Situation

In the first almost three months of 2025, 131 human cases have been confirmed, with 53 deaths. In comparison, 61 cases were reported throughout 2024, 30 of which were fatal. The cases are located in Bolivia (1 case, 1 death), Brazil (81 cases, 31 deaths), Colombia (31 cases, 13 deaths), and Peru (18 cases, 8 deaths), with cases reported beyond the traditionally affected Amazon region.

New Cases and Risk Factors

Particularly concerning are the new cases reported since October 2024 in the department of Tolima, Colombia, which indicates the virus is appearing in areas not previously affected in past years. In these regions, activities such as agriculture represent a risk factor for exposure to the virus. The increase in cases and their geographic spread highlights the urgent need to strengthen surveillance, prevention, and control measures to contain the disease.

Epidemiological Situation in Brazil

In addition, the epidemiological situation in the state of São Paulo, Brazil, with 34 cases and 19 deaths, is worrying due to its proximity to densely populated urban centers, increasing the risk of a larger outbreak.

Understanding Yellow Fever

Yellow fever is a serious viral disease transmitted by mosquitoes, which can be fatal but is preventable through vaccination. The vast majority of the cases detected have involved individuals who were not vaccinated.

PAHO’s Response

In an alert issued on March 27, PAHO calls for intensifying vaccination efforts in at-risk areas, aiming for coverage rates above 95%. Vaccination is the most effective tool to combat the disease. PAHO also recommends that countries review their vaccine stocks, ensure rapid response plans for outbreaks, and make sure travelers to endemic areas are informed and vaccinated.

History of Yellow Fever in the Americas

Since the yellow fever epidemic in Brazil between 2016 and 2018, the public health threat of the disease has resurfaced in the Americas. The yellow fever virus remains in a sylvatic cycle between specific species of mosquitoes and non-human primates in 13 countries and territories of the region. Since 1960, it has caused 9,591 human cases and 3,444 deaths.

Risk Assessment

In February, based on the increase in cases across several countries during the last months of 2024 and the first weeks of 2025, PAHO published a risk assessment in which it considered the risk of yellow fever outbreaks in the region to be high.

Conclusion

PAHO will continue to monitor the situation and support countries in adopting the best strategies for preventing and controlling yellow fever. The organization’s efforts, combined with the cooperation of countries and individuals, are crucial in mitigating the spread of the disease and protecting public health in the Americas.

Frequently Asked Questions (FAQs)

Q: What is yellow fever?
A: Yellow fever is a serious viral disease transmitted by mosquitoes, which can be fatal but is preventable through vaccination.

Q: How many cases of yellow fever have been reported in 2025?
A: As of March 22, 131 human cases have been confirmed, with 53 deaths.

Q: What is PAHO doing to combat the disease?
A: PAHO is calling for intensifying vaccination efforts in at-risk areas, reviewing vaccine stocks, ensuring rapid response plans for outbreaks, and informing travelers to endemic areas.

Q: Can yellow fever be prevented?
A: Yes, yellow fever is preventable through vaccination, and the vast majority of cases detected have involved individuals who were not vaccinated.