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Epidemiological Update Yellow fever in the Region of the Americas - 16 May 2025

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Situation at a glance

From 29 December 2024 and as of 26 April 2025 (with data for Ecuador updated as of 2 May 2025), a total of 212 confirmed human cases of yellow fever, including 85 deaths, have been reported to WHO by five countries in the Region of the Americas (case fatality rate (CFR) 40%). The cases have been reported in the Plurinational State of Bolivia, Brazil, Colombia, Ecuador and Peru. The 212 confirmed yellow fever cases reported so far in 2025 represent a threefold increase compared to the 61 confirmed cases reported in 2024. WHO is supporting affected countries in implementing coordinated actions to respond to the yellow fever cases and outbreaks. This includes enhancing preventive measures, strengthening surveillance and case management, improving risk communication and community engagement, and implementing immunization activities. The current yellow fever situation in the Americas is driven by increased sylvatic transmission cycles. The occurrence of yellow fever cases outside of the Amazon basin, combined with high fatality, varying vaccination coverage across affected countries, and limited vaccine supply, contributes to the overall classification of yellow fever risk in the Region of the Americas, especially in endemic countries, as high. WHO emphasizes the importance of active surveillance, timely laboratory testing, cross-border coordination, and information sharing. Vaccination remains the primary means for the prevention and control of yellow fever. WHO continues to support countries in expanding vaccination coverage through routine immunization programs and mass vaccination campaigns to enhance population immunity and reduce the risk of outbreaks.

Description of the situation

Between 29 December 2024 and 26 April 2025 (with data for Ecuador as of 2 May 2025), a total of 212 confirmed human cases of yellow fever, including 85 deaths (CFR 40%), have been reported to WHO by five countries in the Region of the Americas. The cases were reported from the following countries: Plurinational State of Bolivia (three cases, including one death (CFR 33%)); Brazil (110 cases, including 44 deaths (CFR 40%)); Colombia (60 cases, including 24 deaths (CFR 40%)); Ecuador (four fatal cases (CFR 100%)) and Peru (35 cases, 12 deaths (CFR 34%)) (Figure 1).

In 2024, human cases of yellow fever were reported mainly across the Amazon region of Bolivia, Brazil, Colombia, Guyana, and Peru. In 2025, however, cases have been detected mainly in areas outside the Amazon region, including in the state of São Paulo, Brazil and the Tolima department, Colombia. The 212 confirmed yellow fever cases reported so far in 2025 in the Americas represent a threefold increase compared to the 61 confirmed cases reported in 2024.

Overview by countries

Bolivia (Plurinational State of)

Since the beginning of 2025, Bolivia has reported three confirmed human cases of yellow fever, including one fatal case (CFR 33%), as of 26 April 2025. The cases were reported in the departments of Beni (one case), La Paz (one fatal case), and Tarija (one case). The fatal case had no history of yellow fever vaccination, whereas the other two cases reported having been vaccinated. All three cases were confirmed by Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) testing and had a history of entering forested areas. Additionally, an epizootic event (death of non-human primates) was confirmed in the municipality of San Buenaventura in the department of La Paz.

Brazil

Since the beginning of 2025, Brazil reported 110 confirmed human cases of yellow fever, including 44 fatal cases (CFR 40%), as of 26 April 2025. Cases were reported in the states of Minas Gerais (10 cases, including five deaths), Pará (44 cases, including seven deaths), São Paulo (55 cases, including 31 deaths), and Tocantins (one fatal case). The majority of cases (95 cases; 89.6 %) were male, with ages ranging from 10 to 75 years. Symptom onset occurred between 2 January and 2 April 2025. Only one case had a documented history of yellow fever vaccination.

All cases reported exposure to wild and/or forested areas, either through occupational or recreational activities.

Colombia

Since the beginning of the yellow fever outbreak in early 2024 through 26 April 2025, a total of 83 confirmed yellow fever cases, including 37 deaths, have been reported in Colombia.

In 2025, a total of 60 confirmed cases of yellow fever were reported, including 24 deaths, as of 26 April 2025. The cases were residents of the following departments: Caldas (one fatal case), Cauca (one fatal case), Guaviare (one fatal case), Meta (two fatal cases), Putumayo (three cases, including one death), and Tolima (52 cases, including 18 deaths). The cases ranged in age from 2 to 83 years, with onset of symptoms between 6 January and 18 April 2025. All cases had a history of exposure to areas classified as at risk for yellow fever, defined by the country. Only two of the confirmed cases had a documented history of yellow fever vaccination.

As of 29 April 2025, 29 yellow fever epizootics in non-human primates have been reported, including 27 in the department of Tolima and two in the department of Huila.

Ecuador

Since the beginning of 2025 and as of 2 May, four confirmed fatal cases of yellow fever have been reported, from the provinces of Morona Santiago (one fatal case) and Zamora Chinchipe (three fatal cases). The cases ranged in age from 25 to 55 years, with onset of symptoms between 16 March and 2 May 2025. All four cases had a history of exposure in wild and/or forested areas, due to occupational activities, and were confirmed by RT-PCR.

Peru

Since the beginning of 2025, 35 confirmed cases of yellow fever, including 12 deaths, were reported in the Departments of Amazonas (22 cases, including seven deaths), Huánuco (one fatal case), Junín (three cases), Loreto (two cases, including one death) and San Martin (seven cases, including three deaths), as of 26 April 2025. Of the confirmed cases, 31 (88.6%) were male, with ages ranging from 6 to 57 years, and date of onset of symptoms between 15 January and 12 April 2025. All cases had a history of exposure in wild and/or forested areas, due to agricultural work activities, and 71.8% of the cases had no history of vaccination against yellow fever*.*

Epidemiology

Yellow fever is an epidemic-prone, vaccine-preventable disease caused by an arbovirus transmitted to humans primarily through the bites of an infected Aedes spp. and Haemagogus spp. mosquitoes. The incubation period ranges from 3 to 6 days. Many infected people do not experience symptoms, but when they occur, the most common are fever, muscle pain with prominent back pain, headache, loss of appetite, and nausea or vomiting. In most cases, symptoms disappear after 3 to 4 days. However, a small percentage of cases progress to a more severe, toxic phase characterized by systemic infection affecting the liver and kidneys. These individuals may have high-grade fever, abdominal pain with vomiting, jaundice and dark urine caused by acute liver and kidney failure. Bleeding may also occur from the mouth, nose, eyes, or gastrointestinal tract. Among those who develop severe disease, approximately 50% may die within 7 to 10 days. Yellow fever is prevented by an effective vaccine, which is safe and affordable. A single dose of yellow fever vaccine is sufficient to confer sustained immunity and life-long protection against yellow fever disease. A booster dose of the vaccine is not needed. The vaccine induces effective immunity in 80–100% of recipients within 10 days, and in more than 99% of people within 30 days.

Public health response

To respond to yellow fever outbreaks, public health measures have been implemented at the regional, national and various sub-national levels, including:

Coordination

The countries have implemented coordination actions to respond to the identified yellow fever cases and outbreaks, focusing on strengthening preventive measures, improving surveillance and implementing vaccination actions.

  • Bolivia has conducted interprogrammatic and intersectoral coordination, including coordination with the Autonomous Municipal Governments, through the Emergency Operating Committees (COEM by its acronym in Spanish), involving the Departmental Immunization Committees (CDI by its acronym in Spanish), the technical teams of the Expanded Program on Immunization (PAI by its acronym in Spanish) and epidemiology of the Departmental Health Services, Social Organizations, SENASAG, Ministry of Education, among others to respond to the identification of Cases.
  • Brazil has installed the Emergency Operational Committee for Dengue and other Arboviruses, and a meeting of the Technical Advisory Committee on Arboviruses (CTA-Arbovirus) has been held, with the participation of the Minister of Health, members of the CTA, and ad hoc experts. The Emergency Operational Committee has convened meetings with the states of Amapá, Minas Gerais, Pará, São Paulo and Tocantins to align actions in response to yellow fever.
  • Colombia has issued regulations that organise and update guidelines for preparedness, organization, and response to alert and emergency situations in municipalities with yellow fever cases. Additionally, it declared a health emergency throughout the national territory due to the active circulation of the yellow fever virus. It has also carried out national risk assessments to define the level of risk for the country. The last assessment conducted in epidemiological week 16 (ending date 19 April 2025) escalated the general risk level of the country from high risk to very high risk.
  • In Ecuador, following the confirmation of the first case of yellow fever in 2025, the Ministry of Public Health (MSP), in coordination with the National Institute for Public Health Research (INSPI) and the WHO, undertook actions to assess the existence of risks and take the necessary measures to protect the population.
  • In Peru, multisectoral actions have been carried out under the One Health approach between the Ministry of Health, the National Agrarian Health Service, the National Forest and Wildlife Service, and the National Service of Natural Areas Protected by the State, mainly to promote integrated surveillance of yellow fever.

At the regional level, in February 2025, the WHO conducted a rapid risk assessment to assess the risk to public health associated with the increase in yellow fever cases in the last quarter of 2024 and early 2025 in endemic countries of the Americas Region. The assessment concluded that the overall risk of this event in the Region of the Americas, especially in endemic countries, was classified as “High" with a "High" confidence level based on the available information.

Surveillance

Regarding epidemiological surveillance actions in the countries that have reported cases during 2025, the following actions are implemented:

  • Bolivia, in accordance with national protocols for the immediate notification of suspected cases, Bolivia has implemented response measures including, sample collection from suspected cases, activation of rapid response teams, active case-finding in communities and health facilities, rapid vaccination monitoring, risk analysis related to the potential urbanization of the jungle mosquito vectors. Active search for unvaccinated febrile patients in affected areas and neighbouring communities, as well as monitoring and follow-up of contingency actions. In addition, active case detection is carried out in areas or communities where cases or deaths in non-human primates have been reported. Investigations and notifications of epizootics in non-human primates have also been initiated to support early detection and control efforts.
  • Brazil has published informative notes that update the epidemiological scenario of yellow fever and present the results of the workshop of the Yellow Fever Modelling Group, highlighting the priority municipalities to intensify surveillance and immunization during the 2024/2025 seasonal monitoring period, in support of arbovirus surveillance and control actions. Workshops have been held in municipalities of Minas Gerais and São Paulo to strengthen surveillance strategies, update and discuss yellow fever risk models and define priority areas for surveillance and immunization actions. Technical support has been provided to municipalities for the investigation of suspected and confirmed cases in human and non-human primates. In addition, technical visits are made to the states to support the surveillance and control of arboviruses.
  • In Colombia, the departments with active cases continue to deploy immediate response teams to carry out public health actions. These actions include epidemiological field investigations, rapid coverage monitoring, institutional active search, active community search, entomological studies, contact tracing, and actions related to the vector-borne disease program.
  • In Ecuador, health brigades are actively intervening in the prioritized sectors, reinforcing preventive and control actions.
  • Peru has implemented actions aimed at strengthening surveillance and human resource skills for the detection and notification of suspected cases and outbreak control with a community approach. Active institutional search including febrile icterohemorrhagic (jaundice and haemorrhage) syndrome as a differential diagnosis.o Additionally, it has issued a national epidemiological alert and regional alerts and has implemented the Situation Room for Vaccine-Preventable Diseases. In addition, surveillance of yellow fever in non-human primates (epizootics) has been promoted within the framework of the surveillance and integrated response of zoonoses; in this regard, there is a multisectoral tool developed for the integrated surveillance of yellow fever in non-human primates, with the start of pilots in the San Martín and Ucayali regions during 2025.

At the regional level, WHO has implemented the following actions:

  • Publication of technical guidance documents for use at the subnational and national levels, including case definitions, instructions for sample collection and references to laboratories, as well as guidelines for the management of control efforts.
  • Preparation and maintenance of a detailed map of yellow fever risk areas in the Region of the Americas, based on associated environmental conditions.
  • To facilitate access to historical and current information on yellow fever cases in the region, the Yellow Fever Dashboard in the Region of the Americas was published, allowing for the monitoring of the situation at both regional and country levels.
  • Regional alerts, epidemiological updates and risk assessments have been issued, including recommendations for Member States.
  • Face-to-face trainings and webinars on epidemiological surveillance, epizootic surveillance and entomology of yellow fever have been conducted for endemic countries.
  • Support has been provided to member states in implementing epizootic and entomological surveillance.

Laboratory

At the country level, the following actions have been carried out:

  • Implementation of guidelines for sample collection and processing.
  • Brazil maintains stocks of RT-PCR diagnostic tests available in the country's public health laboratory network. In addition, it has advanced the sequencing of 13 complete genomes of the virus from human samples of cases registered in the state of Pará.
  • In Colombia, samples of suspected cases of yellow fever are sent to the departmental public health laboratory. This laboratory sends samples for processing to the National Reference Laboratory of the National Institutes of Health. Through the Arbovirus Laboratory of the Virology Group at the National Institute of Health, the detection of yellow fever is carried out through serological or virological studies, making this the only centre in Colombia that performs such detection.

At the regional level, WHO has implemented the following actions:

  • Strengthening of the laboratories within the Network of Arbovirus Diagnostic Laboratories of the Americas, providing guidelines, protocols, and reagents.
  • Publication of recommendations for laboratory surveillance and diagnosis of yellow fever.
  • Providing technical assistance and monitoring laboratories in endemic countries.
  • An external quality assessment for the molecular detection of yellow fever was conducted in 18 laboratories from the 13 endemic countries.

Case Management

At the regional level, an international technical group of experts on re-emerging diseases supports technical cooperation activities at the country level. In addition, the countries in the Region have implemented protocols and clinical guidelines for the management of yellow fever cases. Some of the specific actions taken by countries that have registered cases include:

  • Improvement of health services in the areas of case presentation and training on yellow fever for health personnel, including doctors and nurses, to ensure timely care of yellow fever cases.
  • Close clinical monitoring of cases to identify warning signs and progression to severe forms. Establishment of health centres for the referral of severe cases and the timely referral of serious cases to hospitals with greater resolution capacity.

Immunization

  • In Bolivia, when cases are identified, actions are taken to vaccinate individuals around detected cases, tracing, and control vaccination cards. In addition, vaccinations have been carried out at transit points, and orientations have been conducted for people who regularly travel to areas with a high incidence of yellow fever in the country.
  • In Brazil, vaccination strategies have been constantly reinforced through technical notes. Vaccine doses are distributed according to the standard schedule, and additional doses are distributed according to state demand.
  • Colombia has issued circulars establishing transitional measures for the implementation of vaccination against yellow fever from 9 months of age in the municipalities of the endemic corridor. These are the criteria to extend vaccination to people over 59 years of age in the endemic corridor of 54 prioritized villages in the municipalities of Tolima, where human cases or epizootics have occurred. Within the framework of the emergency declaration, a strategy of mobilization and intensification of vaccination was implemented, which includes a risk classification for municipalities. This classification, which is regularly updated on the website of the Ministry of Health and Social Protection and includes: very high-risk municipalities, where there is active circulation of the virus, human cases, epizootics or presence in eco-epidemiological corridors; high-risk municipalities, with environmental conditions that favour the possible appearance of cases; and low-risk municipalities, where there are currently no conditions for the appearance of outbreaks.
  • In Ecuador, priority has been given to the groups at greatest risk: the population between 12 months and 59 years of age, people with high internal mobility, miners, farmers, poultry workers and those who plan to travel to endemic areas, for vaccination actions against yellow fever. Additionally, the country has implemented an obligation to present the International Certificate of Vaccination upon arrival in the country to travellers from Peru, Colombia, Bolivia and Brazil, effective since 12 May 2025.

At the regional level, WHO promotes mass vaccination campaigns. Guidelines for stock management have been published. In addition, countries in the Region have implemented the methodology of "Microplanning of high-quality vaccination activities" in routine programs or vaccination intensification campaigns. This methodology enabled a focus on detailed planning at the local level to optimize access and a timely response to vaccine-preventable disease outbreaks.

Entomological Surveillance and Vector Control

At the regional level, vector surveillance and control capacities that were developed as part of the arbovirus response are being leveraged for surveillance in countries where yellow fever outbreaks have occurred. In addition, the countries that have registered cases have implemented the following actions:

  • Bolivia has implemented actions to eliminate breeding sites in peri-urban and rural areas, conducted focal fumigation in communities with active outbreaks and maintained entomological surveillance.
  • Brazil has published a technical note containing guidelines on vector control actions of Aedes aegypti and Aedes albopictus in places with suspected or confirmed human and/or non-human primate cases of yellow fever. In addition, it has conducted a collection of fauna for entomological surveillance in the municipality of Breves, state of Pará.
  • Ecuador has proposed the installation of various entomological traps to facilitate early detection and an effective response to possible outbreaks, with the support of the National Institute for Public Health Research. Likewise, comprehensive healthcare teams are carrying out investigations of larvae and pupae to control mosquito breeding foci.

Risk Communication and Community Engagement

In countries where outbreaks have occurred, risk communication and community engagement have been enhanced to reinforce their commitment to immunization and recommended actions.

  • The countries of the Region have Safe Vaccination Committees, which play a fundamental role in risk communication and the development of messages and technical information for the different target audiences. They also assist in analyzing and responding to Events Presumably Attributable to Vaccination or Immunization, ensuring an evidence-based approach.
  • Countries with cases disseminate publications regarding the health risk posed by yellow fever, as well as audiovisual materials aimed at preventing and recognizing signs and symptoms and seeking medical attention. To achieve this, they use various means and communication channels, such as institutional website and social networks.
  • Publications have been issued to alert travellers and people who go to areas at risk for yellow fever to take the necessary protective measures, including the verification of the history of vaccination or application of the vaccine against yellow fever at least 10 days before their trip.
  • Brazil has conducted training in the use of SISS-Geo for participatory community policing. Additionally, it utilizes other means to alert the population through the social networks of the Ministry of Health and the State and Municipal Health Secretariats.

WHO risk assessment

Yellow fever is an acute haemorrhagic disease endemic to, or with endemic regions in twelve countries and one territory in the Americas Region: Argentina, the Plurinational State of Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Panama, Paraguay, Peru, Suriname, Trinidad and Tobago, and the Bolivarian Republic of Venezuela.

Clinically, yellow fever can be difficult to distinguish from other viral haemorrhagic fevers, such as arenavirus, hantavirus, or dengue. In context, where dengue outbreaks are ongoing, early diagnosis can be particularly challenging, especially in settings where healthcare workers may have limited experience in recognizing and managing yellow fever cases. The disease has historically caused numerous epidemics with high mortality rates.

From 1960 to 2022, a total of 9,397 confirmed cases of yellow fever, including 3,315 deaths, were reported in the Americas. The majority of these cases were reported by three countries: Bolivia 16% (1553 cases, including 516 deaths), Brazil 36% (3443 cases, including 1192 deaths), and Peru 35% (3281 cases, including 1343 deaths). 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), Brazil (six cases, including four deaths), Colombia (two cases including one death), and Peru (28 cases, including 16 deaths) (Figure 2).

In 2024, 61 human cases of yellow fever were confirmed in the Americas, resulting in 30 fatalities, distributed across five countries. Bolivia reported eight cases, including four deaths; Brazil reported eight cases, including four deaths; Colombia reported 23 cases, including 13 deaths; Guyana reported three cases; and Peru reported 19 cases, including nine deaths.

The public health risk in yellow fever-endemic countries in the Region of the Americas is considered "high" based on the WHO Rapid Risk Assessment conducted in February 2025, given the increase in yellow fever cases in the last quarter of 2024 and early 2025. Most cases reported during 2024 did not have a documented history of yellow fever vaccination. Even though regional yellow fever vaccine coverage levels were not optimal before the COVID-19 pandemic (61%), vaccination coverage declined significantly between 2020 and 2023, increasing the number of susceptible populations in all endemic countries. In 2023, Ecuador and Guyana achieved yellow fever vaccine coverage greater than or equal to 95%, and only two countries, Suriname and Trinidad and Tobago, had coverage between 90% and 94%. In addition, six countries had yellow fever vaccine coverage of less than 80%: Argentina, the Plurinational State of Bolivia, Brazil, Panama, Peru, and the Bolivarian Republic of Venezuela.

The occurrence of yellow fever cases outside of the Amazon basin in Colombia (Tolima) and Brazil (São Paulo) is concerning. In the newly affected areas of Colombia, populations are largely susceptible in the absence of prior large-scale preventive interventions.

The risk of introduction into urban settings exists in the Americas whenever sylvatic transmission cycles are increased, with potential for international spread if urban contingency measures are inadequate.

The increase in confirmed yellow fever cases in the Americas has highlighted the need to strengthen surveillance, vaccination of at-risk populations, and risk communication strategies for people moving to areas where vaccination is recommended. The systematic exposure of yellow fever cases to sylvatic-related activities, whether occupational or for leisure, stresses the need for approaches targeting individuals working in wild or forested areas, such as loggers, farmers, and ecotourism professionals. Best practices in clinical management, with an emphasis on early recognition and detection, timely referral, and treatment of severe cases, must be disseminated to healthcare workers in endemic areas. In addition, countries should have vaccine stockpiles, depending on vaccine availability, to ensure a rapid response to possible outbreaks. The overall risk of this event in the Region Americas, especially in endemic countries, is classified as high.

Although endemic countries in the Americas have strengthened surveillance, laboratory diagnostics, and vaccination capacities, the global supply of yellow fever vaccines has been fluctuating in recent years, which can reduce access to vaccination for susceptible people and lead to a lack of response to yellow fever outbreaks. As of early 2025, the available yellow fever vaccine supply for the region is also severely constrained and insufficient to cover the routine regional demand for the year.

WHO advice

Yellow fever is an epidemic-prone, mosquito-borne vaccine-preventable disease transmitted to humans by infected mosquitoes, primarily Aedes sp. and Haemagogus species. The urban proliferation of Aedes spp. mosquitoes, particularly Aedes aegypti, which are active during the day, can significantly amplify transmission, especially in densely populated areas.

Surveillance: WHO emphasizes the importance of active surveillance, cross-border coordination, and information sharing. Investigating and testing suspected cases is crucial for controlling and preventing outbreaks. It is recommended that surveillance be enhanced with investigations and laboratory tests of suspected cases.

Vaccination as a Primary Prevention Tool: Vaccination is the primary means for preventing and controlling yellow fever. The WHO's Eliminate Yellow Fever Epidemics (EYE) strategy prioritizes vaccination in countries reporting yellow fever, integrating it into routine immunization schedules for individuals aged 9 months and above. WHO supports the expansion of vaccination coverage through routine programs and mass vaccination campaigns to enhance communal immunity.

Vector Control and Risk Communication: Effective vector control in urban settings, along with general mosquito bite avoidance strategies, is recommended to prevent disease transmission. WHO urges Member States to inform travellers about yellow fever risks, preventive measures, and to seek immediate medical attention if symptoms arise. This approach helps prevent the establishment of local transmission cycles through infected travellers.

International Travel and Trade: All international travellers aged 9 months and above heading to areas at risk of yellow fever transmission (i.e. areas with evidence of persistent or periodic yellow fever virus transmission), as determined by WHO, are advised to get vaccinated. The vaccine is deemed safe and effective, offering lifelong protection. However, vaccination recommendations for infants under 9 months, as well as for pregnant or breastfeeding women, are nuanced, advocating for vaccination in high-risk scenarios after weighing the benefits against potential risks.

Under the IHR, it is a country’s prerogative to require proof of yellow fever vaccination from incoming and/or outgoing travellers. For international travel purposes, the administration of yellow fever vaccine shall be documented in the International Certificate of Vaccination or Prophylaxis (ICVP); and the documented administration of one single dose of WHO-approved yellow fever vaccine, conferring lifelong immunity, shall be accepted as valid.

Given the evolving nature of yellow fever transmission, WHO advises Member States to remain updated with the latest information and guidelines available on the WHO International Travel and Health website. Local health authorities are encouraged to collaborate closely with WHO and other relevant stakeholders to implement effective yellow fever prevention and control measures, ensuring the safety and well-being of populations at risk.

WHO advises against imposing travel or trade restrictions related to the current yellow fever outbreak in the Region of the Americas. Continuous efforts to educate travellers on preventive measures, including vaccination, are encouraged.

Further information

Citable reference: World Health Organization (16 May 2025). Disease Outbreak News; Yellow fever in the Region of the Americas. Available at: https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON570

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