Yellow fever outbreaks persist across Africa, Americas — WHO

Yellow fever is making a troubling comeback across Africa and the Americas, prompting fresh warnings from the World Health Organisation (WHO) over the risks posed by low vaccination coverage, climate change, and expanding mosquito habitats.

In a global update released on Wednesday, the WHO said transmission remained active throughout the first months of 2026, following a significant resurgence in the Americas last year.

Between January and May, six countries in the Americas reported 79 confirmed cases, while three African countries recorded 16 confirmed infections, with additional suspected cases under investigation. Health authorities also detected multiple outbreaks among non-human primates, an important indicator of ongoing viral circulation.

The mosquito-borne disease remains endemic in tropical regions of Africa and South America. Although many infections are mild, severe cases can cause jaundice, internal bleeding, and organ failure, with fatality rates reaching up to 50%.

The WHO warned that unvaccinated populations remain particularly vulnerable. In Africa, average yellow fever vaccine coverage in high-risk countries was estimated at just 65% in 2024, below the 80% threshold considered necessary for strong population protection.

The Americas continue to experience the effects of a major resurgence that began in late 2024. The region recorded 241 cases and 100 deaths between late 2024 and early 2025, marking an eightfold increase compared with the previous year. Colombia has been among the countries most affected during the current wave.

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Health experts say a combination of environmental and social factors is driving transmission, including favourable mosquito breeding conditions, population movement, and urban expansion into forested areas where the virus naturally circulates.

While no imported cases have been reported outside Africa and the Americas, the WHO warned that increasing international travel and the spread of mosquito vectors could create opportunities for future outbreaks elsewhere.

The agency is urging countries to strengthen disease surveillance, laboratory testing, and vaccination programmes. More than 35 million people have been vaccinated through preventive and emergency campaigns since the start of 2025.

“Vaccination remains the most effective tool for preventing yellow fever,” the WHO said, noting that the most recent cases occurred in people who had not received the vaccine.

Despite the current outbreaks, the WHO assesses the global risk as low, although it remains moderate in regions where the disease is historically endemic.