Yellow Fever in Travellers

Yellow fever (YF) is an acute haemorrhagic flavivirus infection that is transmitted primarily by mosquitoes of the Haemogogus, Sabethes and Aedes genera, and affects humans and non-human primates (NHP). The disease is endemic and enzootic in several tropical regions in the Americas and Africa, with periodic upsurges and outbreaks. In its most severe form, it causes a haemorrhagic fever which has a high (20–50%) case-fatality rate. Besides the availability of safe and effective vaccines since 1937, the existence of a sylvatic cycle of transmission involving wild mosquitoes and NHPs makes eradication impractical. In the last years, explosive outbreaks have been documented in Africa and South America. The risk of major YF epidemics, especially in densely populated urban settings, has greatly increased due to reinvasion of urban settings by Aedes aegypti, rapid urbanization, intense population mobility, and waning immunization coverage. Importantly, people travelling to endemic regions represent a population at risk for YF virus exposure, and once infected, may contribute to disease spread to non-endemic areas. Vaccination is recommended for people aged ≥9 months who live in or travel to endemic areas. The unusual resurgence events emphasize the relevance for considering YF as a serious threat to human health as well as the need for better understanding and monitoring the disease.