Disease Description: Yellow fever is a viral disease that is transmitted to humans through the bite of infected mosquitoes. Illness ranges in severity from an influenza-like syndrome to severe hepatitis and hemorrhagic fever which can be fatal.
Risk to Travelers: The disease occurs only in sub-Saharan Africa and tropical South America where it is endemic and intermittently epidemic. In a country where yellow fever may be transmitted risk of exposure may not be uniform thoughout the country (see tables). A traveler's risk of acquiring yellow fever is determined by various factors, including immunization status, location of travel, season, duration of exposure, occupational and recreational activities while traveling, and the local rate of virus transmission at the time of travel. Although reported cases of human disease are the principal indicator of disease risk, case reports may be absent because of a high level of immunity in the population (e.g., due to vaccination campaigns), or because cases are not detected by local surveillance systems. Only a small proportion of yellow fever cases is recognized and officially reported because the involved areas are often remote and lack specific diagnostic capabilities.
Prevention - Vaccine: Yellow fever is preventable by a relatively safe, effective live virus vaccine. For all eligible persons, a single injection of vaccine should be administered subcutaneously. Vaccination may actually be required to enter certain countries.
Vaccine Adverse Effects: Reactions to yellow fever vaccine are generally mild. However, very serious neurologic (encephalitis, Guillain-Barre, acute disseminated encephalomyelitis) and systemic (yellow fever vaccine-associated viscerotropic disease (YEL-AVD)) reactions, including death have occurred.
The risk for adverse reactions appears to be age related. Infants younger than 6 months of age should not be vaccinated because they are more susceptible to the serious adverse reaction of YEL-AND (also known as postvaccinal encephalitis). Persons over age 60 should be carefully evaluated for the need for yellow fever vaccine.
A history of thymus disease has recently been identified as a contraindication to yellow fever vaccine.
The safety of yellow fever vaccination during pregnancy has not been well established, and the vaccine should be administered to pregnant women only if travel to an area with risk of yellow fever is unavoidable.
Infection with yellow fever vaccine virus poses a theoretical risk for travelers with immunosuppression in association with HIV infection; leukemia, lymphoma, or generalized malignancy; with a history of thymus disease or thymectomy; or who are receiving corticosteroids, alkylating drugs, antimetabolites, or radiation.
Vaccine Booster Recommendations: Booster doses of YFV are needed every ten years.
Information adapted from CDC Health Information for International Travel (the Yellow Book), http://www.cdc.gov/travel/yellowbook/2010/table-of-contents.htm