Yellow fever

Yellow fever is an epidemic-prone, vaccine-preventable disease caused by a virus transmitted by infected Aedes s.p., Haemagogus s.p. and Sabethes s.p. mosquitoes ^[1]. These mosquitoes breed in domestic, forest (sylvatic), and semi-domestic environments ^[1]. Due to its high-impact and potential for international spread, yellow fever poses a significant threat to global health security ^[1].

Initial illness typically includes fever, headache, generalized body aches, nausea, vomiting, and weakness, with symptoms usually resolving within 3–4 days after an incubation of 3–6 days ^[1][2]. Approximately 15% of infected individuals progress to severe disease marked by recurrent high fever, jaundice, bleeding, organ failure, and shock, with about half of these patients dying within 7–10 days ^[1][2]. Severe presentations may resemble other febrile or haemorrhagic conditions, complicating early diagnosis ^[1][2].

Yellow fever is endemic in 47 countries in Africa and Central and South America, and roughly 90% of yearly reported cases arise in Sub-Saharan Africa ^[3]. Infected travellers can introduce the virus to yellow-fever-free countries, though sustained spread requires competent mosquito vectors, suitable climate, and an animal reservoir ^[3]. Outbreaks are especially concerning in overcrowded settings with poor water and waste services, and WHO estimates actual outbreak cases may be 10 to 250 times unreported figures ^[3][4].

The disease is transmitted by infected mosquitoes, principally Aedes species that bite during daytime, as well as Haemagogus and Sabethes, which become infected after biting an infected human or monkey ^[1][3][2]. It cannot be passed person-to-person by contact, and urban epidemics can emerge where unvaccinated populations have increased contact with vectors ^[3][2]. Sylvatic and semi-domestic cycles blur as human settlements expand into forested transmission zones ^[4].

Vaccination is the primary preventive measure, with emergency and long-term immunization critical during outbreaks and for travellers to endemic areas ^[1][4]. Vector control relies on surveillance of Aedes aegypti and environmental management, though insecticide-treated bed nets are limited given daytime biting ^[1][2]. The EYE strategy (2017–2026) and reaching hard-to-reach populations are public-health priorities to ensure vaccine equity ^[3][4].

1. 1 World Health Organization. Yellow fever [Internet]. cited 3 Sept 2026. Available from: https://www.who.int/news-room/fact-sheets/detail/yellow-fever
2. 2 World Health Organization. Yellow fever [Internet]. cited 3 Sept 2026. Available from: https://www.who.int/health-topics/yellow-fever
3. 3 World Health Organization. Yellow fever [Internet]. cited 3 Sept 2026. Available from: https://www.who.int/news-room/questions-and-answers/item/yellow-fever
4. 4 Tuells J et al. Yellow Fever: A Perennial Threat. Arch Med Res. 2022 Nov. PMID: 36404585. doi: 10.1016/j.arcmed.2022.10.005. PubMed: https://pubmed.ncbi.nlm.nih.gov/36404585/