Yellow fever is a viral disease transmitted by infected mosquitoes. WHO describes it as epidemic-prone and vaccine-preventable, with most of the global burden occurring in Africa. It is also present in parts of Latin America, and international spread remains a public-health concern.
How is yellow fever transmitted?
WHO states that infected Aedes, Haemagogus and Sabethes mosquitoes can transmit the virus. These mosquitoes breed in domestic, forest and semi-domestic environments. The mosquitoes that transmit yellow fever mainly bite during the day, which is why WHO notes that insecticide-treated bed nets are less effective for this disease than for infections spread mainly by night-biting mosquitoes.
A mosquito-borne route means that yellow fever is different from infections that spread directly through coughing, touching or sharing food. This page cannot determine whether a particular mosquito bite created a risk; location, outbreak activity, vaccination history and individual circumstances all matter.
Where is outbreak risk concentrated?
WHO classifies 27 African countries and 13 Latin American countries as being at high risk for yellow-fever outbreaks. The organization estimates that tens of thousands of severe infections and deaths occur each year in Africa and the Americas, with most of the burden in Africa.
Risk is not established by a country name alone. Public-health conditions, the area within a country, current outbreak information and travel requirements can change. Families planning travel should use current advice from an appropriate public-health or travel-health authority.
What symptoms does WHO describe?
The incubation period is usually 3–6 days. WHO lists fever, headache, general body aches, nausea, vomiting and weakness among the initial symptoms. These symptoms often disappear within 3–4 days.
WHO states that about 15% of infected people develop severe infection. Severe illness can include a return of high fever, jaundice, vomiting, bleeding, organ failure and shock. Jaundice means yellowing of the skin and eyes. WHO describes this phase as dangerous and says jaundice is an indication of severe disease that justifies hospitalization.
Why can diagnosis require testing?
Early symptoms are not specific to yellow fever. WHO says severe cases can resemble malaria, leptospirosis, viral hepatitis, other haemorrhagic fevers such as dengue, and poisoning. Laboratory methods differ according to the stage of illness: WHO describes RT-PCR testing of blood in the early stage and antibody testing later.
A symptom list cannot establish the diagnosis. A person with concerning symptoms after possible exposure or travel needs assessment through an appropriate health service.
What treatment information does WHO provide?
WHO says there is no specific antiviral treatment routinely used for yellow fever. Clinical care is mainly supportive and may include rest and hydration, management of fever, liver or kidney failure, and treatment of secondary bacterial infections. The level of care can range from care at home to hospitalization or emergency referral depending on severity.
This description is not a home-treatment plan. Decisions about testing, monitoring, fluids, medicines or hospital care require qualified clinical assessment.
What does WHO say about vaccination?
WHO identifies vaccination as the most effective preventive measure. Its fact sheet says one dose provides lifelong immunity and that a booster is not needed. It also lists groups for whom vaccination is not recommended, including infants under 9 months, pregnant women except during outbreaks, people with severe egg allergy, and people with severe immunodeficiency or thymus disorders.
Those statements do not decide whether a particular child should receive a vaccine. Age, health, destination and national recommendations must be considered by an appropriate clinician or vaccination service. Countries may also require proof of vaccination from travellers under the International Health Regulations.
What other prevention measures does WHO list?
WHO’s vector-control measures include eliminating mosquito breeding sites such as standing water, using larvicides in water containers, wearing protective clothing and using repellents. Vector surveillance helps public-health programmes assess urban outbreak risk.
For outbreaks, WHO emphasizes rapid detection, laboratory confirmation, emergency vaccination and longer-term immunization measures. These are coordinated public-health actions rather than steps an individual webpage can direct.
When should medical advice be sought?
Yellow fever can become severe, and its early symptoms overlap with other illnesses. Seek prompt professional assessment when yellow fever is suspected, particularly after travel or residence in an affected area. Urgent symptoms such as jaundice, bleeding, breathing difficulty, marked weakness, confusion or signs of shock require emergency evaluation.
How should the vaccine information be understood for children?
WHO’s fact sheet presents yellow-fever vaccination as both individual protection and a population measure for preventing outbreaks. Routine childhood immunization and catch-up activities in high-risk countries are part of the global strategy. The protection statement applies to an eligible person who receives an appropriate vaccine dose; it does not remove the need to check age restrictions, health conditions or destination-specific advice.
The source specifically says vaccination is not recommended for infants under nine months. That age statement should not be used to make a decision without professional advice during an outbreak or before travel. A vaccination service can apply the current national guidance and determine whether an exemption or another plan is appropriate.
Why is rapid outbreak detection important?
WHO says laboratory confirmation, emergency vaccination and investigation of each confirmed case are central to outbreak control. Reported cases may substantially underestimate the true number during an outbreak. Surveillance therefore helps authorities act before every infection has been individually counted.
The EYE strategy combines mass vaccination in high-risk countries, routine immunization, catch-up work, urban preparedness and early case detection. These measures explain why prevention involves health systems and communities as well as individual mosquito protection.
References
- World Health Organization. Yellow fever, 20 October 2025. Source reviewed 4 October 2026.