This vector-borne disease is a tropical, urban and rural viral infection, transmitted by Aedes aegypti and Haemagogus mosquitoes. These mosquitoes bite mostly during daylight hours. It is found only in central Africa and intertropical America, but fatal cases of yellow fever are possible in unvaccinated tourists visiting rural zones in endemic areas. The disease is absent from tropical Asia (up to the present time), but the prevalence of both the vector (aedes) and the reservoir (primates) explain why many Asian countries demand proof of vaccination against yellow fever in travelers from infected areas or zones where the disease is endemic. Areas where yellow fever virus is present far exceed those officially reported.

Countries with risk of yellow fever transmission (Source: WHO, 2008  ●  For up to date information visit WHO site):

Among the "special risk vaccines for travelers", the yellow fever is the most important and is compulsory for all travelers to and from endemic zones. It must be administered in internationally approved vaccination centers and registered in international vaccination certificates (new "international certificate of vaccination or prophylaxis" in force since June 2007 − IHR, 2005).

The yellow fever vaccine is recommended for:

- Adults and children ≥ 9 months of age travelling or living in any african country listed above, regardless of where they will be in the country (urban and rural areas);

- Adults and children ≥ 9 months of age travelling or living outside urban areas of all other endemic countries (listed above); and

- Laboratory personnel who routinely work with yellow fever virus.

Protection starts ten days after vaccination or immediately after the booster (every ten years). The available heat-stable vaccine is "live attenuated" and effective ten days after primary vaccination (one dose); boosters should be given every ten years. Must be applied subcutaneously, 0.5 ml (one dose) in adults, and half dose in children over nine months of age.

The vaccine is contraindicated in children younger than six months old and is not recommended for those aged 6-8 months; however, in case of increased risk of exposure the vaccine may be applied to infants older than six months. Contraindications to vaccination also include: true allergy to egg protein, cellular immunodeficiency (congenital ou acquired) and symptomatic HIV infection.

There is a theoretical risk for the fetus with the vaccination during pregnancy, but this aspect must be weighed against the risk to the mother remaining unvaccinated and travelling to a high-risk area. However, pregnant women should be advised not to travel to places where exposure to yellow fever may occur.

Fernando Costa Silva, 1999 (last update: 2009)