Yellow Fever Disease

Yellow fever occurs in certain jungle locations of South America and Africa where the virus is maintained in a cycle among forests, mosquitoes, and monkeys. In South America sporadic infections occur almost exclusively in forestry and agricultural workers who are exposed occupationally in or near forests. In Africa the virus is transmitted in the moist savanna zones of West Africa during the rainy season, and infections occur principally among children. At intervals, massive outbreaks resulting in thousands of cases develop in urban locations and villages in the dry savanna of Africa.

Yellow fever is a viral disease transmitted between humans by a mosquito. General precautions to avoid mosquito bites should be followed. These include the use of insect repellent, protective clothing, and mosquito netting. Yellow fever is a very rare cause of illness in travelers, but most countries have regulations and requirements for yellow fever vaccination that must be met prior to entering the country.

Yellow Fever Vaccine Requirements

Yellow fever vaccine is the only vaccine that may be required for entry into certain countries of Africa and South America. After immunization an International Certificate of Vaccination is issued and will meet entry requirements for all persons traveling to or arriving from countries where there is active or a potential for yellow fever transmission. The Certificate is good for 10 years. Most countries will accept a medical waiver for persons with a medical contraindication to vaccination (for example, infants less than 4 months old, pregnant women, persons hypersensitive to eggs, or those with a immunosuppressed condition). CDC recommends obtaining written waivers from consular or embassy officials before departure.

Doctors or travelers can receive vaccine requirements based on their travel itineraries by contacting state or local health departments for the most recent recommendations or by checking this web site. Vaccine is obtained from Yellow Fever Vaccine Centers designated by your state health department. Consult your local health department for yellow fever vaccination sites near you. The CDC does not keep a list of registered yellow fever vaccination sites.

Yellow fever vaccine is a live attenuated viral vaccine. A single dose confers long-lived immunity lasting 10 years or more. If at continued risk of yellow fever infection, a booster dose is needed every 10 years. Administration of immune globulin does not interfere with the antibody response to yellow fever vaccine.

Yellow Fever Precautions

The vaccine generally is associated with few side effects: fewer than 5% of vaccines develop mild headache, muscle pain, or other minor symptoms 5 to 10 days after vaccination. However, three groups of individuals should not receive the vaccine, and a fourth group should be closely evaluated.

The vaccine is contraindicated for three groups:

Yellow fever vaccine should never be given to infants under 4 months of age due to a risk of developing viral encephalitis. In most cases, vaccination should be deferred until 9 to 12 months of age.

Pregnant women should not be vaccinated because of a theoretical risk that the developing fetus may become infected from the vaccine.

Persons hypersensitive to eggs should not receive the vaccine because it is prepared in embryonated eggs. If vaccination of a traveler with a questionable history of egg hypersensitivity is considered essential, an intradermal test dose may be administered under close medical supervision.

A fourth group should be closely evaluated before administering the vaccine:

Persons with an immunosuppressed condition associated with AIDS or HIV infection, or those with their immune system altered by other diseases, such as leukemia and lymphoma, or through drugs and radiation, should not receive the vaccine. People with asymptomatic HIV infection may be vaccinated if exposure to yellow fever cannot be avoided.

In all cases the decision to immunize an infant between 5 and 9 months of age, pregnant women, or an immunocompromised patient should be made on an individual basis. The physician should weigh the risks of exposure and contracting the disease against the risks of immunization, and possibly consider alternative means of protection.

Yellow Fever Certificate

After immunization an International Certificate of Vaccination is issued and is valid 10 days after vaccination to meet entry and exit requirements for all countries. The Certificate is good for 10 years. You must take the Certificate with you. Travelers who have a medical reason not to receive the yellow fever vaccine should obtain a medical waiver. Most countries will accept a medical waiver for persons with a medical reason not to receive the vaccine. When required, CDC recommends obtaining written waivers from consular or embassy officials before departure. A physician's letter clearly stating the medical reason not to receive the vaccine might be acceptable to some governments. It should be written on letterhead stationery and bear the stamp used by a health department or official immunization center to validate the International Certificate of Vaccination. Check embassies or consulates for specific waiver requirements.

© Center for Disease Control

Credits: National Center for Infectious Diseases