Yellow Fever Cases Surge in the Americas, WHO Issues Alert

The World Health Organization (WHO) and the Pan American Health Organization (PAHO) have issued a renewed alert regarding rising cases of yellow fever across the Americas, with a significant increase observed in 2025 compared to the previous year. Outbreaks are occurring in regions where the disease was historically uncommon, raising concerns about broader transmission and vaccine access.

Recent Surge in Cases

According to a recent report from PAHO and WHO, a total of 346 confirmed human cases of yellow fever, resulting in 143 deaths, were recorded in seven countries across the Americas during 2025. This represents a 5.6-fold increase from the 61 confirmed cases reported in 2024. PAHO Epidemiological Alert

As of epidemiological weeks 1 and 7 of 2026 (January and February), 34 confirmed infections and 15 deaths due to yellow fever have been reported in humans, specifically in:

• Bolivia: 1 death
• Colombia: 25 cases, including 13 deaths
• Peru: 2 cases
• Venezuela: 6 cases, including 1 death

Throughout 2025, cases were distributed as follows:

• Bolivia: 8 cases, including 2 deaths
• Brazil: 120 cases, including 48 deaths
• Colombia: 125 cases, including 46 deaths
• Ecuador: 11 cases, including 8 deaths
• Guyana: 1 death
• Peru: 49 cases, including 19 deaths
• Venezuela: 32 cases, including 19 deaths

Drivers of the Increase and Risk Factors

The current yellow fever situation in the Americas is primarily driven by increased sylvatic transmission cycles – the natural cycle of the virus between mosquitoes and non-human primates. However, the emergence of cases outside the Amazon basin, combined with varying vaccination coverage and limited vaccine supply, contributes to a high overall risk in the region, particularly in endemic countries. WHO Disease Outbreak News

Recent research indicates that land-use changes, specifically the expansion of urban areas into forested regions, are playing a significant role in increasing human exposure to the virus. As human settlements encroach upon natural habitats, the transmission cycle is disrupted, leading to more frequent spillover events. UC Santa Barbara Marine Science Institute

WHO and PAHO Recommendations

In response to the escalating situation, the WHO and PAHO are urging member states to:

• Strengthen surveillance systems to detect and respond to outbreaks rapidly.
• Intensify vaccination efforts, particularly among at-risk populations.
• Ensure adequate information and protection for travelers visiting affected areas.
• Enhance clinical management of severe cases, including maintaining reserve doses of the yellow fever vaccine for rapid outbreak response.
• Promote cross-border coordination and information sharing.

Vaccination remains the primary means of preventing and controlling yellow fever. WHO continues to support countries in expanding vaccination coverage through routine immunization programs and mass vaccination campaigns. WHO Disease Outbreak News

Yellow Fever: A Reminder

Yellow fever is a viral hemorrhagic disease transmitted by infected mosquitoes. Symptoms typically include fever, headache, jaundice, muscle pain, and bleeding. In up to 50% of severe cases, it can lead to liver and kidney failure. Health Policy Watch