According to the global health agency, a total of 95 confirmed human cases of yellow fever were recorded between January and May 2026, underscoring the persistence of the mosquito-borne disease despite ongoing vaccination efforts.
In a statement released on Wednesday, WHO disclosed that six countries in the Americas accounted for 79 confirmed infections, alongside multiple epizootics—outbreaks among non-human primates that serve as important indicators of virus circulation. Three African countries also reported 16 confirmed cases during the same period.
The organisation further revealed that an additional 32 suspected cases are currently under investigation across five countries, raising fears that the actual burden of the disease could be higher due to gaps in disease surveillance and detection.
It said, “WHO’s rapid risk assessment concluded that unvaccinated populations in areas with a history of yellow fever transmission face the greatest threat. The highest risk occurs where low vaccination coverage overlaps.”
WHO noted that yellow fever transmission in the Americas has continued into 2026 following a rise in infections recorded throughout 2025, a trend that reflects sustained viral circulation and growing public health concerns in affected countries.
The agency also emphasised the significance of outbreaks among monkeys and other non-human primates, describing them as early warning signs of continued virus activity in forest environments.
According to the organisation, “Multiple epizootics in non-human primates confirm active sylvatic circulation, signalling ongoing virus activity in forest mosquitoes and heightened spillover risk to humans.”
In Africa, WHO said yellow fever activity remains persistent across 13 high-risk countries participating in the Eliminate Yellow Fever Epidemics (EYE) Strategy, a coordinated initiative designed to reduce the frequency and impact of outbreaks across the continent.
The organisation explained that outbreaks reported between October 2025 and May 2026 coincided with seasonal environmental conditions such as increased rainfall, rising temperatures and a surge in mosquito populations, all of which create favourable conditions for virus transmission.
It stated, “These conditions increase vector density and human exposure, especially where vaccination coverage is low. No imported cases were detected outside the two affected WHO regions so far.”
Despite the absence of imported cases beyond Africa and the Americas, WHO cautioned that the global threat remains significant.
“However, expanding vector suitability, rapid urbanisation, climate shifts, and increased human mobility create conditions conducive to international spread,” the organisation noted.
To minimise the risk of wider outbreaks, WHO urged countries to strengthen disease surveillance systems, improve laboratory testing capacity, enhance cross-border collaboration and ensure timely information sharing for rapid detection and response.
The organisation stressed that identifying infections early in both humans and animals is essential to preventing urban transmission of the disease.
It added, “Early detection in both human and animal populations is critical to prevent urban transmission cycles. Vaccination remains the primary means for prevention and control of yellow fever.
“WHO continues to support countries in expanding routine immunisation programmes and preventive vaccination campaigns to boost population immunity and reduce outbreak risk.”