Yellow Fever in the Americas 2025 - A Pan American Health Organisation Update

One hundred and thirty-one cases have been notified in 4 countries (Bolivia, Brazil, Colombia and Peru) to 26 March 26, 2025. There have been 53 deaths. This is a high fatality rate and provides a warning to those who might be considering travel to forested areas of South America.

Vaccination is available for the prevention of yellow fever.

Country Breakdown

Brazil - Highest case numbers in 2025

Most of the cases (81) have been reported in Brazil (states of Sao Paolo, Para, Minas Gerais and Tocantins).  All cases had a history of travel to forested areas and none were vaccinated.  The report also notes many deaths (> 400) in non-human primates.  Peak cases occurred in February/ March.

Colombia - New outbreaks linked to forest areas

Thirty-one cases have been reported in Colombia. All occurred in areas known to be at risk for yellow fever. The departments included Caqueta, Putumayo and Tolima.

Tolima reported its first case in October 2024. The outbreak is mostly confined to municipalities bordering the Bosque de Galilea natural park. It may be related to higher than usual numbers of mosquitoes due to increased rainfall. According to the report, none of the cases had documented yellow fever vaccination.

In Tolima, vaccination rates for yellow fever are lower than the national average (54% v 64%) with those older than 40 years much less likely to be vaccinated.

Peru - Agricultural workers at risk

Eighteen cases have been reported in Peru. The departments of Huanuco, San Martin and Amazonas have been named. All cases were male, agricultural workers and none were vaccinated.

Bolivia - Case reported in La Paz

One case has been reported in the municipality of Palos in the La Paz department of Bolivia. He was also unvaccinated. See full report - Epidemiological Alert - Yellow fever in the Americas Region - 26 March 2025

Key factors contributing to outbreaks

Several contributing factors have been identified

• Travel to forested areas where yellow fever transmission is active.
• Gaps in vaccination coverage, particularly among older populations.
• Increased mosquito densities, potentially linked to climatic factors like higher rainfall.
• Spillover events from non-human primates to humans.

Yellow Fever vaccination facts

The yellow fever vaccine (Stamaril in Australia) is a live attenuated vaccine that offers highly effective, durable protection.

Key points:

• Immunity develops in 80–100% of individuals within 10 days after vaccination, and in 99% by 30 days.
• A single dose confers lifetime immunity, based on the WHO guideline change in July 2016 (previously, a 10-year booster was recommended).
• The vaccine is safe and crucial for travellers to endemic areas.

Vaccination continues to be a key element in preventing both individual infection and large outbreaks.

Additional strategies for Yellow Fever control

While vaccination remains essential it cannot be the sole strategy.

Lessons from previous outbreaks in Angola and Brazil (2016–2017) highlight the risk of urban transmission when the virus spills over into densely populated areas resulting in large numbers of cases and many deaths.

Additional strategies include:

• Mosquito control and environmental management.
• Surveillance and early outbreak detection.
• Public education on preventive measures.

WHO’s global strategy to eliminate yellow fever epidemics (EYE 2017-2026) can be sourced here.