Yellow Fever Outbreaks

Yellow Fever Outbreaks 2024

The yellow fever (YF) virus has been endemic in tropical areas of Africa and The Americas for many years. As of 2024, the World Health Organization (WHO) says about forty-seven countries in Africa (34) and Central and South America (13) are either endemic to yellow fever or have regions endemic to yellow fever. The WHO reported on March 20, 2024, that 13 countries in the WHO African Region documented probable and confirmed cases of yellow fever, with a preliminary case fatality rate of 11%. As of May 2024, yellow fever outbreaks in the Region of the Americas were reported by the Pan American Health Organization (PAHO), including cases in Bolivia, Brazil, Colombia, Guyana, and Peru. In 2023, Costa Rica identified Geographical Zones at risk of yellow fever virus transmission. On April 4, 2024, the U.K.'s Tavel Health Pro confirmed seven YF cases, including four fatal cases, have been reported in South America between January and March 2024.

Yellow Fever Virus History

Scientists believe that yellow fever has existed for about 3,000 years. The disease originated in Africa and spread to the Americas in the 17th century. In the 18th and 19th centuries, yellow fever was considered one of the most dangerous infectious diseases, causing outbreaks throughout the Americas, Africa, and Europe.

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. In February 2024, the Republic of South Sudan's health ministry reported 48 suspected and two confirmed Yellow Fever cases from Yambio, Nzara, Tambura, Ibba, Ezo, and Maridi Counties of Western Equatoria State. Since the beginning of 2023, and as of late February 2024, 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 re-assessed as moderate.

The Americas Yellow Fever Outbreaks

In 2024, the U.K. reported yellow fever cases in Colombia (three fatal cases), Guyana (two cases), and Peru (two cases, including one death). In 2023, four countries in the Region of the Americas reported 41 confirmed cases of yellow fever, including 23 deaths: Bolivia (five cases, including two deaths) (4,5), Brazil (six cases, including four deaths) (6), Colombia (two cases, including one death) (7,8), and Peru (28 cases, including 16 deaths)

Brazil experienced its largest-recorded yellow fever outbreak in 2018, reports the PAHO. In Brazil, yellow fever transmission historically occurs within a sylvatic cycle in the Amazonian region. In the extra-Amazonian region, yellow fever outbreaks occur, potentially causing infection in humans with irregular periodicity under favorable conditions for transmission. In March 2024, a study that compared the detection and phylogenetic analysis of the YF virus in two neotropical primates (NTP), a Callithrix detected in the previous epidemic period (2016–2020), and a Callicebus griffons, showing a new introduction of YF in 2023.

The U.S. Centers for Disease Control and Prevention (CDC) recommends that all travelers ≥9 months of age going to the entire states of Acre, Amapá, Amazonas, Distrito Federal (including the capital city of Brasília), Espirito Santo,* Goiás, Maranhão, Mato Grosso, Mato Grosso do Sul, Minas Gerais, Pará, Paraná, Rio de Janeiro (including the city of Rio de Janeiro and all coastal islands), the Rio Grande do Sul, Rondônia, Roraima, Santa Catarina, São Paulo (including the city of São Paulo and all coastal isles), and Tocantins and designated areas of Bahia and Piauí. Vaccination is also recommended for travelers visiting Iguaçu Falls. The CDC published an Emerging Infectious Disease Synopsis, Volume 29, Number 3—March 2023, describing five yellow fevervaccine–associated viscerotropic disease (YEL-AVD) cases in two familial clusters during the 2017–2018 YF vaccination campaign in São Paulo state, Brazil.

Brazil's Anvis confirmed proof that yellow fever vaccination is required when visiting certain areas. As of May 2023, Australia, the U.S. CDC, Hong Kong, and the United Kingdom have issued travel alerts regarding Brazil's yellow fever outbreaks.

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.