Preventing Yellow Fever
Yellow fever is a viral hemorrhagic infection that is common in tropical Africe and Latin America. It is caused by the yellow fever (YF) cirus. Its importace lies in its virulence and increasing incidence among travelers to the endemic areas.
Yellow fever is spread by mosquitoes that feed on wild animals infected with the YF virus. The mosquitoes then transfer the infection to people who happen to be in the jungle. On their return to towns or cities, the infected individuals may get bitten by domestic mosquito Aedes aegypti, which then transmits YF to others.
Following a bite from an infected mosquito the virus multiplies at the site of the bite and spreads to adjacent lymph nodes, liver, spleen, bone marrow and heart muscle.
The virus is found in the bloodstream during the incubation period of three to six days and the early stages of the illness. The YF viruse in the bloodstream are spread to another person following ingestion by the blood-feeding Aedes aegypti.
The clinical manifestations of an infection are varied and include flu-like symptoms or febrile illness with jaundice or fatal hemorrhagic disease. YF infection may be mistaken for a number of other infectious diseases such as malaria, dengue and hepatitis. The onset of illness is abrupt with fever, chills, headaches, backache, muscle aches, nausea, vomiting, congestion of the face and eyes and a slow heartbeat. The fever lasts three to four days and is followed by complete recovery in those with the transient non-jaundice type of infection.
However, the illness progresses in about 15 percent, with or without a break of one to two days, to a more serious variety. There is fever, vomiting, upper abdominal pain, yellowness of the eyes and the skin (jaundice. Liver failure, kidney failure, fits and hemorrhagic tendencies due to decreased production of clotting factors and intravascular coagulation may occur. Coma may also occur.
About 30 to 50 percent of those with liver and/or kidney failure die a week or so after the onset of illness. Those who survive may have prolonged fatigue and weakness. However, there is complete recovery of their liver and kidney function.
There is no specific treatment available for YF infection. Treatment is only supportive, such as for dehydration and bacterial infection YF is a very serious illness and public health problem in the endemic areas. There are an estimated 200,000 cases annually with 90 percent occurring in Africa. About 30 percent of those infected die.
The WHO estimates that the risk of YF infection to an unvaccinated person entering an endemic area in Africa is one in 267 and the risk of death is one in 1,333. The risks in Latin America are 10 times lower.
Although there are estimated to be more than 10 million travelers to endemic areas, the incidence of imported cases of YF in nonendemic countries is low because of high YF vaccination rate among travelers.
The yellow fever vaccine is a live attenuated vaccine, that is, live disease-producing virus modified in the laboratory so that it stimulates the production of antibodies. YF vaccine can be safety given simultaneously with other vaccines like diphtheria-pertussis-tetanus (DPT), polio, measles, hepatitis B, hepatitis A and typhoid.
YF vaccines are recommended for all children aged 12 months and above, older children and adults living in endemic areas. It is also given to individuals whomove into an endemic area to stay. When outbreaks of YF occur, mass vaccination is carried out as soon as possible.
Yf vaccination is required for all individuals aged nine months and above traveling to and from endemic countries unless they have medical conditions that make vaccination unsuitable.
Vaccination should be done at least 10 days prior to arrival in the endemic area.
YF vaccination has to be carried out in approved centers with WHO-approved vaccines in order for entry in the International Certificate of Vaccination. This certificate has to be made available when entering or leaving an endemic country.
The YF vaccine is very effective. Protective antibody levels are found in 90 percent of vaccines within 10 days and 99 percent within a month. The protection appears to last for 30 to 35 years. However, there is insufficient evidence to support a change in the International Health Regulations for travelers to endemic areas to show proof of valid YF vaccination within the preceding 10 years.
YF vaccines are well-tolerated although mild reaction such as headache, muscle ache and weakness can occur within a few days after vaccination, in 10 to 30 percent of vaccines. Serious adverse reactions are very rare. They include hypersensitivity reactions, vaccine-associated neurological disease and vaccine-associated viscerotropic disease.
Hypersensitivity reactions are usually due to reaction to the eggs used in the production of the vaccine and rarely, gelatin, which is used to stabilize the vaccine.
Vaccination is not given to infants below nine months of age, individuals with severe allergy to eggs, pregnant women and severely immuno-compromised individuals. However, the YF vaccine may be given to pregnant women and infants during an epidemic








