BRIEFING LEAFLET
24HUPBL03
02 July 2024

Yellow Fever Information for Pilots
NOTE
This paper is an update to, and supersedes 10MEDBL05, of the same name.
INTRODUCTION
Yellow fever has been known for over 400 years, and the name originates from thejaundice that some patients acquire. The disease is caused by a mosquito-spread virus.
The virus can infect both humans and primates. It is endemic in African and Americancountries close to the equator. Most of those infected remain asymptomatic, but about
15% develop a hemorrhagic infection and with an approximate 50% mortality rate.
Symptoms include fever, muscular pain, headache, chills, loss of appetite, nausea and/orvomiting, and often a low pulse rate despite the fever. There is no specific treatment for
the virus. Yellow fever vaccination is effective and may be required to enter certain
countries. It is suggested that all pilots who fly to, or over the endemic yellow fever
countries take this vaccine.
On July 11, 2016, the World Health Organization adopted the policy that all Yellow Fever
vaccinations were valid for the lifetime of the person vaccinated. This applies to allexisting and new vaccinations. No modifications need to be made to existing
vaccination cards. However, some health authorities recommend the booster forindividual protection and some countries may require the booster.
VIRUS
Yellow fever virus belongs to the Flavivirus group. The virus infects both humans andprimates and is carried from one animal to another by a biting mosquito. Mosquitoes
are also able to pass the virus via infected eggs to their offspring. Mosquitoes are thetrue reservoir of the virus. The mosquitoes bite during daylight hours and at altitudes ofup to 2,500 metres.

EPIDEMICS
The virus is constantly present with low levels of infection (i.e. endemic) in some tropicalareas of Africa and the Americas, but this viral presence can amplify into epidemics.
There are 200,000 estimated cases of yellow fever (with 30,000 deaths) per year.
However, due to underreporting, only a small percentage of these cases are identified.
Small numbers of imported cases also occur in countries free of Yellow Fever. Although
the disease has never been reported from Asia, this region is at risk because theappropriate primates and mosquitoes are present.
TRANSMISSION
There are three types of transmission cycles for Yellow Fever: Sylvatic, Intermediate, andUrban. All three cycles exist in Africa, but in South America, only Sylvatic and Urban
yellow fever occur.
Sylvatic (or “jungle”) yellow fever
In tropical rainforests, yellow fever occurs in primates that are infected by wild
mosquitoes. The infected monkeys can then pass the virus on to other mosquitoes thatfeed on them. These infected wild mosquitoes bite humans entering the forest, resulting
in sporadic cases of Yellow Fever. The majority of cases are in young workers in theforest (logging, etc). On occasion, the virus spreads beyond the affected individual.
Intermediate yellow fever
In humid or semi-humid savannahs of Africa, small-scale epidemics occur. These behave
differently from urban epidemics; many separate villages in an area suffer cases
simultaneously, but fewer people die from infection. Semi-domestic mosquitoes infectboth primate and human hosts. This area is often called the “zone of emergence”, whereincreased contact between human and infected mosquito leads to disease. This is themost common type of outbreak seen in recent decades in Africa. It can shift to a more
severe urban-type epidemic if the infection is carried into a suitable environment (withthe presence of domestic mosquitoes and unvaccinated humans).
Urban Yellow Fever
Large epidemics can occur when migrants introduce the virus into areas with highhuman population density. Domestic mosquitoes (of one species Aedes aegypti) carrythe virus from person to person with no primates involved in transmission. Theseoutbreaks tend to spread outwards from one source to cover a wide area.

2GEOGRAPHY
In Africa, Yellow Fever exists in countries within a band from 15°N to 10°S of theequator. In the Americas, yellow fever is endemic in nine South American countries andin several Caribbean islands. Bolivia, Brazil, Colombia, Ecuador, and Peru are considered
at greatest risk.
SYMPTOMS
The incubation period (i.e. the time in which the symptoms develop) is three to six days
and most infections seem asymptomatic. However, if the symptoms develop, there aretwo different phases: “acute” and “toxic”. The acute phase is characterized by fever,muscle pain, headache, shivers, loss of appetite, nausea and/or vomiting and theparadoxically slow pulse despite the fever.
15% of the patients enter a “toxic phase” within 24 hours. Fever reappears and several
body systems are affected. Patients develop jaundice and abdominal pain with vomiting.
They also suffer from different hemorrhagic manifestations, including bleeding from themouth, nose, eyes, and/or stomach. Kidney function deteriorates; this can range frommild dysfunction to complete renal failure. Half of patients in the “toxic phase” diewithin 10-14 days. The remainder recover without significant organ damage.
DIAGNOSIS
Yellow fever is difficult to recognise, especially during the early stages. Antibodies, orthe virus itself, can be detected in the blood, but these tests require highly trainedlaboratory staff using specialised equipment and materials.
TREATMENT
There is no specific antiviral treatment available and thus the treatment is based upon
symptoms. Dehydration and fever can be corrected with oral rehydration solution andpainkillers. Any superimposed bacterial infection should be treated with an appropriate
antibiotic. Intensive care may improve the outcome of seriously ill patients.
VACCINATIONThe Yellow Fever vaccine is safe and highly effective. Immunity occurs within one week
in 95% of people vaccinated. A single dose of vaccine provides protection for thelifetime of the vaccinated person. However, some health authorities recommend abooster for individual protection and some countries may require it.

3There have been reports of a small number of serious adverse reactions, including
deaths, following Yellow Fever vaccination; most of these reactions occurred in elderly
persons. However, the risk to unvaccinated individuals who visit endemic countries is far
greater than the risk of a vaccine-related adverse event. It remains important for all
travellers at risk to be vaccinated; nonetheless, yellow fever vaccination should not beprescribed for individuals who are not at risk of exposure to infection.
Side effects of the vaccination are usually slight. They include local reactions at the siteof inoculation (in up to 10 % of those vaccinated), after four to six days there may be
more general reactions, such as an elevated body temperature, malaise, headache andmuscle pain which usually subside within 24 hours. Contraindications for vaccination are
acute febrile diseases within the last two weeks, immuno suppression and immune
defects, corticoid medication, allergy against chicken protein, and age (<6 months).
Only Authorised Vaccination Centres may give the Yellow Fever vaccine and one musthave an official vaccination certificate as proof of the vaccination. This is mandatorywhen entering certain countries of the endemic zones and, after having visited endemic
zones within the last six days, when entering certain other countries of the endemic
zones and outside. The list of countries that require vaccination can be found, forexample, from the International Travel and Health booklet that is accessible from WHO
web pages www.WHO.int. The validity of the certificate begins 10 days from thevaccination day, by then the person has developed immunity.

SOURCESAs of May 2024
https://www.who.int/topics/travel/en/
https://wwwnc.cdc.gov/travel/yellowbook/2018/infectious-diseases-related-totravel/yellow-fever©2024 The International Federation of Air Line Pilots’ Associations. This publication is provided for information purposes only, in allcases pilots should follow their company’s guidance and procedures. In the interest of flight safety, reproduction of this publication inwhole or in part is encouraged. It may not be offered for sale or used commercially. All reprints must credit IFALPA.

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