Global Yellow Fever Situation: Africa and the Americas, 2025–2026

Yellow fever is a vector-borne viral disease endemic to parts of Africa and the Americas.

Following a surge in the Americas during 2025, transmission activity persisted into early 2026.

From January to late May 2026, six countries in the Americas reported 79 confirmed human cases.

Multiple epizootics were also documented, signalling active sylvatic circulation of the virus.

In Africa, sustained transmission continued across 13 high-risk countries classified under the EYE Strategy.

Three African countries reported 16 confirmed cases from January to May 2026.

An additional 32 suspected cases remained under investigation in five other African countries.

A rapid risk assessment evaluated vaccination coverage, evidence of viral circulation, and vector competence.

Unvaccinated populations in areas with a history of yellow fever transmission face the greatest risk.

Seasonal factors such as rainfall, temperature, and mosquito abundance further shape transmission dynamics.

Cases in previously unaffected areas suggest viral introduction and an elevated urban transmission risk.

No imported cases were detected outside the two WHO regions most affected in 2025–2026.

Expanding vector suitability, urbanisation, climate shifts, and human mobility sustain the risk of international spread.

WHO stresses the need for active surveillance, timely laboratory testing, and cross-border information sharing.

Vaccination remains the primary prevention and control tool for yellow fever globally.

Sylvatic yellow fever transmission in high-risk areas has been strongly driven by rainfall and mosquito ecology.

Twenty-six countries in the WHO African Region and one in the Eastern Mediterranean Region are high-risk.

Of those 27 countries, 26 have introduced yellow fever vaccine into their routine immunisation schedules.

Average immunisation coverage across the African Region reached only 65% in 2024, below the target.

Since 2023, eight previously unaffected African countries have detected new yellow fever cases.

In 2025, outbreaks were recorded in Angola and the Central African Republic, requiring emergency vaccination.

From January to May 2026, confirmed cases were reported in Burkina Faso, the Central African Republic, and Cameroon.

Recurrent outbreaks are straining health systems and increasing the risk of cross-border spread.

All 13 high-risk countries in the Americas include yellow fever vaccine in their routine immunisation programmes.

The Americas recorded 241 cases and 100 deaths between late 2024 and early 2025.

This represented an eightfold increase in cases compared with the previous year.

Bolivia, Brazil, Colombia, Ecuador, Peru, and Venezuela reported 79 confirmed cases from January to May 2026.

Colombia was the most affected country, largely due to sylvatic exposure among unvaccinated visitors.

Outside Africa and the Americas, yellow fever risk is primarily associated with imported cases.

Yellow fever is transmitted by day-biting mosquitoes of the Aedes, Haemagogus, and Sabethes species.

Globally, yellow fever is estimated to cause 67,000 to 173,000 severe cases annually.

Estimated annual deaths from yellow fever range from approximately 31,000 to 82,000.

Transmission occurs in three epidemiological cycles: sylvatic, intermediate, and urban.

The urban cycle poses the greatest risk for large-scale outbreaks in densely populated areas.

The incubation period is typically three to six days after an infective mosquito bite.

Approximately 15% of infections progress to severe disease with jaundice, haemorrhage, and multi-organ failure.

Among those with severe disease, the case fatality rate can reach approximately 50% within 7–10 days.

Surveillance systems likely underreport yellow fever because its clinical presentation overlaps with malaria and dengue.

During epidemics, actual infection numbers may be 10 to 250 times higher than reported figures.

A single dose of yellow fever vaccine confers lifelong immunity and remains the most effective preventive measure.

WHO has strengthened coordination across the African Region through regular engagement with Member States and EYE partners.

Regional reviews of PRNT-positive cases were conducted for several African countries, including Nigeria and Uganda.

In the Americas, response was managed under a structure equivalent to a Level 2 emergency.

A multidisciplinary Incident Command System was established to coordinate the regional outbreak response.

In the Americas, epizootic surveillance in nonhuman primates was strengthened as an early warning system.

Preventive mass vaccination campaigns in Africa in 2025 reached approximately 15.2 million people in Katanga Province alone.

Additional preventive campaigns vaccinated 1.6 million in Guinea-Bissau and 9.6 million in three Niger regions.

Reactive vaccination campaigns in Africa from January 2025 to May 2026 reached over one million people in affected districts.

Overall, WHO-supported campaigns reached more than 35 million people in high-risk countries between 2025 and May 2026.

In the Americas, updated regional vaccination guidelines now address fractional dosing and single-dose schedules.

WHO promoted integration of entomological investigations into yellow fever outbreak investigations in the African Region.

In the Americas, regional guidelines for entomological surveillance and vector control for yellow fever were published in 2025.

Yellow fever remains a significant public health threat due to spillover into human populations from forest cycles.