Update of the Immunization Manual chapter on yellow fever

In a nutshell:

Yellow fever continues to be a global concern as outbreaks have failed to be brought under control in a number of countries, mainly in Africa, despite international efforts. The increasing expansion of Aedes aegypti (mosquito vector) into areas far from the tropics, such as Madeira, Cyprus and, more recently, the Canary Islands, means that the risk of indigenous cases of this and other arboviruses needs to be periodically assessed in Europe. . Since 2017, WHO, UNICEF and Gavi have joined forces to develop a comprehensive global strategy to end the yellow fever epidemic (EYE), with mass vaccination as the main focus.

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Introduction

Yellow fever (YF) is a viral disease that has three epidemiological forms of manifestation: a) urban form: occurs in endemic geographic areas and is caused mainly by Aedes aegypti, which transmits the infection after feeding a person in the viremic phase; b) tropical form: an enzootic disease that persists among non-human primates and from which it is transmitted through various vectors to humans, and c) an intermediate form between the previous two: in this case, primates are infected by semi-domestic mosquitoes. and human are interchangeable (more common in endemic areas of Africa).

In Spain, where no human cases have been reported for decades, the presence of the Aedes aegypti mosquito has recently been discovered in the Canary Islands, particularly Gran Canaria, where it appears to have established itself.

At the moment, the risk of indigenous cases of foot and mouth disease occurring is very low, but we must be prepared for the spread of mosquito vectors in our country and other regions of Europe.

Epidemiology and immunization policy update

In 2023, the WHO African Region reported 99 confirmed cases of foot-and-mouth disease, including 8 deaths (case fatality rate 9.3%), in 15 countries. Despite massive vaccination campaigns in some of these countries, many people belonging to vulnerable, migrant or excluded populations did not have access to vaccination. In the Americas, 40 cases of AF were reported in 2023, resulting in 24 deaths (mortality rate 60%). Cases have been reported in Bolivia, Brazil, Colombia and Peru. Most have a history of exposure to wildlife or forested areas due to work or recreation. During the same period, 9 deaths from yellow fever among primates (monkeys) were confirmed in Brazil.

FMD vaccine should be administered during childhood in endemic areas as part of routine vaccination programs and supplementary immunization activities, including emergency outbreak response and recovery campaigns in endemic areas. In Africa, 22 of 27 countries at risk of transmission already included it in their childhood immunization programs in 2017. Ethiopia and South Sudan have not yet included yellow fever vaccine in their routine vaccination schedules.

“EYE” strategy

Following devastating outbreaks in Angola and the Democratic Republic of Congo in 2016, which resulted in cases being exported to China, the End Yellow Fever Epidemic (EYE) Strategy was launched, an effort led by WHO, UNICEF and Gavi to address the changing epidemiology of the disease. re-emergence of mosquitoes and increased risk of urban outbreaks and international spread. EYE is a comprehensive long-term strategy based on lessons learned to end the foot-and-mouth disease epidemic by 2026.

Since 2017, an additional 226 million people in Africa have been protected from foot and mouth disease with a one-dose vaccine that provides lifelong protection. The previous yellow fever initiative protected 108 million people over 8 years. The global coalition EYE Strategy helped accelerate vaccinations during this period.

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