Yellow fever is caused by an arbovirus in the tropical regions of Africa and South America and is spread by mosquitoes. The illness starts out with a mild fever accompanied by a headache, malaise, nausea, and vomiting, and then resolves temporarily. It returns with more severe symptoms including a high fever, vomiting blood plus blood in the stool, jaundice, and heart and kidney damage. Over 50 percent of the cases are fatal.
The vaccine is recommended for all individuals over nine months of age who are traveling to or living in areas that have yellow fever. In addition, certain countries require proof of vaccination if you are arriving from a different country that has yellow fever, even if you only visited that country in transit. The fear is that you will pick up the virus and bring it to the uninfected country.
The yellow fever vaccine is a live, attenuated vaccine. Side effects to the vaccine occur in 25 percent of recipients, but most are temporary and mild. Unfortunately, about one in one hundred thousand recipients develop encephalitis related to the weakened virus in the vaccine. This encephalitis is more common in infants, which is why the vaccine is only recommended for children over nine months of age. In addition, about one in two hundred thousand recipients develop the actual yellow fever illness from the vaccine. As already described, the illness can be severe and fatal. Thus, while the disease is clearly dangerous, the vaccine has rare severe reactions as well.
The vaccine should not be given to anyone who has had a severe allergic reaction to a previous dose of the vaccine or to any component in the vaccine. Because the oral vaccine contains a live, attenuated virus, it is not recommended for any person with a deficiency of the immune system. This would include anyone who has HIV or certain kinds of cancer, is receiving chemotherapy or radiation therapy, or has been on medications that suppress the immune system, such as steroids, for more than two weeks. The vaccine should be given to a pregnant woman only if travel to a high-risk country is unavoidable and the risk of exposure is high.
If there is no medical reason to not give the vaccine, we follow the CDC recommendations. If the CDC recommends this vaccine for a given country, then we also recommend this vaccine for a traveler to that country. The yellow fever vaccine can only be given in certain travel clinics around the country. To find the closest yellow fever clinic near you, contact your local health department or go to http://www2. ncid.cdc.gov/travel/yellowfever/.