Yellow Fever Outbreaks

Yellow Fever Outbreaks April 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 April 15, 2025, the YF virus has become endemic in tropical areas of Africa and 13 countries in the Americas, such as Brazil and Colombia. The WHO reported in March 2025 that the yellow fever case fatality rate is about 39%.

Africa Yellow Fever Outbreak

On March 28, 2024, the U.S. 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 March 31, 2025, the Pan American Health Organization (PAHO) reported outbreaks in Bolivia, Brazil, Colombia, Guyana, and Peru. Between epidemiological weeks 1 and 12 of 2025, 131 confirmed cases of YF were reported in four countries of the Region, 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: implications for the Americas, confirming the high risk of YF outbreaks in the Region.

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 yellow fever outbreak 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 yellow fever cases 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 yellow fever 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 virus has appeared in areas not previously affected in past years in the department of Tolima, Colombia. As of March 2025, there have been 31 cases, with 13 deaths.

Peruvian authorities released an epidemiological alert due to a sharp rise in yellow fever cases in areas of the Peruvian Amazon in 2025, including the districts of Huanuco, San Martin, and Amazonas. As of April 1, 2025, Peru has 29 confirmed cases of yellow fever, with 10 deaths. In comparison, Peru reported 19 confirmed cases of yellow fever with nine deaths for all 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, the Aedes aegypti was seen in Butte County. The American Society for Microbiology posts a history of the emergence of yellow fever outbreaks in the U.S.