Yellow Fever Outbreaks

Yellow Fever Outbreaks May 2025

Scientists believe yellow fever has existed for about 3,000 years, originating in Africa and spreading to the Americas in the 17th century. In the 18th and 19th centuries, yellow fever (YF) was considered one of the most dangerous mosquito-transmitted infectious diseases. According to the World Health Organization (WHO), as of May 1, 2025, the YF virus has become endemic in tropical areas of Africa and 13 countries in the Americas, including Brazil and Colombia. The WHO reported in April 2025 that the yellow fever case fatality rate is about 39%.

Africa Yellow Fever Outbreak

On March 28, 2024, the U.S. Centers for Disease Control and Prevention (CDC) issued a Level 2 Travel Health Notice regarding a yellow fever outbreak in Nigeria. Between January 2024 and November 2024, a total of 29 confirmed YF cases were reported in Nigeria. Since the beginning of 2023, documented probable and confirmed cases of yellow fever have been reported in Burkina Faso, Cameroon, the Central African Republic, Chad, the Republic of the Congo, Côte d'Ivoire, the Democratic Republic of the Congo (DRC), Guinea, Niger, Nigeria, South Sudan, Togo and Uganda. The overall risk at the regional level was reassessed as moderate.

The Americas' Yellow Fever Outbreaks

As of May 2025, the Pan American Health Organization (PAHO) reported outbreaks in Bolivia, Brazil, Colombia, Ecuador, Guyana, and Peru. Over 131 confirmed cases of YF were reported in four countries of the Americas, 53 of which were fatal. In comparison, the PAHO reported 61 YF cases throughout 2024, 30 of which were fatal. In February 2025, the PAHO published a Public Health Risk Assessment related to yellow fever, confirming the high risk of YF outbreaks in the Americas. On April 15, 2025, the U.S. CDC issued a Level 2 - Practice Enhanced Precautions, Travel Helath Advisory regarding YF outbreaks in the Americas.

In Brazil, yellow fever transmission historically occurs within a sylvatic cycle in the Amazonian Region. Between 2020 and 2025, three cases of yellow fever were confirmed in the Peixe and São Salvador regions. São Paulo State Health Department confirmed that 679 human cases were recorded from 2000 to 2023. Brazil experienced its largest recorded outbreak of yellow fever in 2018. For three decades, yellow Fever cases have been confirmed in Pará State, Amazon Region of Brazil. In March 2025, five confirmed deaths and 27 cases of YF were reported on Marajó Island. As of 2025, Australia, the U.S. CDC, Hong Kong, and the United Kingdom have issued travel alerts regarding Brazil's YF outbreaks.

Bolivia reported a confirmed yellow fever case/fatality in February 2025 in the city of Palos Blancos in the La Paz Department. Eight cases occurred in 2024 and five in 2023.

Since October 2024, the YF virus has appeared in areas not previously affected in past years in the Colombian department of Tolima. As of May 2025, there have been 83 cases, with 37 deaths, primarily in Tolima.

The Ecuadorian Ministry of Public Health reported three confirmed cases of yellow fever as of April 2025, including one in the province of Zamora Chinchipe.

Peruvian authorities issued an epidemiological alert due to a sharp rise in yellow fever cases in areas of the Peruvian Amazon in 2025, including the districts of Huánuco, San Martín, and Amazonas. As of April 24, 2025, Peru has reported 32 confirmed cases of yellow fever, resulting in 10 deaths. In comparison, Peru reported 19 confirmed cases of yellow fever, with nine deaths, for the entire year of 2024.

United States Yellow Fever Outbreaks

In the United States, the Butte County Mosquito and Vector Control District in California detected the Aedes aegypti (yellow fever) mosquito in 2023. For the fourth consecutive year, Aedes aegypti mosquitoes were found in Butte County. The American Society for Microbiology provides a history of the emergence of yellow fever outbreaks in the United States.