Yellow fever is an acute tropical disease, caused by an Arbovirus belonging to the Flaviviridae family, transmitted through the bite of infected mosquitoes. It is called "yellow" because of its most prominent symptom, jaundice, which can in some cases manifest as yellow eyes and skin, following possible liver damage. Usually in the 3 to 6 days following infection, a high fever accompanied by chills, headache, muscle aches, nausea, and vomiting occur. Patients with this benign form recover in 3-4 days.
After a remission of 1-2 days, a new bout of fever occurs in 15% of sufferers. Abdominal pain, liver enlargement, jaundice, and bleeding of the skin, mucous membranes, and digestive tract then appear. Mortality caused by this severe form ranges from 20 to more than 50 percent. Tourists are generally affected by the severe form of the disease.
Yellow fever virus is a virus with a single-stranded RNA genome, provided with a pericapsid coating, belonging to the Flaviviridae family, to which it precisely gives its name (from Latin flavus, yellow). To this family belong many other viruses, which are responsible for serious diseases that travelers should pay attention to, such as dengue virus, zika virus, west nile virus, and Japanese encephalitis virus.
The yellow fever virus is native to Africa, and is capable of infecting not only humans but also monkeys: the virus' natural reservoir. The mode of transmission is vector-borne, that is, via mosquitoes. In most cases, the Aedes aegypti, a species adapted to the domestic environment and which stings mainly humans, is responsible, but its "cousin," the Aedes albopictus (the now common tiger mosquito), found in Italy and several parts of Europe, is also capable of acting as a vector. The risk, however, that the tiger mosquito can transmit yellow fever in our country is considered very low.
Currently, yellow fever is present in Africa, where, in rural settings, it has caused severe epidemics with tens of thousands of deaths. It is also present in South America, from Panama to Argentina, especially in the Amazon zone, whereas it has never been detected in Asia.
The vaccine
The yellow fever vaccine is a live attenuated vaccine, so it induces a good immune response without causing the disease. It contains no aluminum.
For a long time, vaccination was recommended every 10 years. Currently, WHO recommends only one dose, which is considered sufficient for lifelong protection. Some countries have not yet adapted their legislation.
Yellow fever vaccination is recommended in some countries and sometimes mandatory for staying in or transiting through most countries in sub-Saharan Africa and those in Latin America that touch the Amazon basin, Panama included.
Vaccination in the over 60s
The side effects of the yellow fever vaccine are similar to all other vaccines, with nausea, fever, headache, and pain at the injection site among the most common. However, rare cases with greater complications have been shown to occur more in individuals over 60 years of age. These include:
- Yellow fever vaccine associated neurological disease (YEL-AND) is a condition that affects the brain and nervous system, causing symptoms such as confusion and problems with movement and coordination. The risk of YEL-AND is estimated as follows: .
- over 60 years of age = 2.2 cases per 100,000 doses of vaccine administered
- under 60 years old = 0.8 cases per 100,000 doses of vaccine administered
- Yellow fever vaccine associated viscerotropic disease (YEL-AVD) is similar to yellow fever itself with multi-organ failure and death in about 48% of cases. The risk of YEL-AVD is estimated as follows: .
- over 60 years of age = 1.2 cases per 100,000 doses of vaccine administered
- under 60 years of age = 0.3 cases per 100,000 doses of vaccine administered
As a result, for patients over 60 years of age, evaluation by a physician who can weigh risks and benefits before administration is appropriate.
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