Yellow fever

What is it?

Yellow fever is an acute viral haemorrhagic disease (a disease causing excessive internal bleeding) which can be transmitted to humans via the bites of mosquitos infected with yellow fever virus (YFV).

What to look for?

The incubation period of yellow fever is 3 to 6 days. The initial signs and symptoms are generally non-specific and include fever, chills, myalgia (muscle pain), fatigue, and nausea or vomiting. Symptoms usually resolve within 3 to 4 days. 

Approximately 15–25% of cases will enter a second, more toxic phase within 24 hours after recovering from initial symptoms. This phase presents with a return of high fevers and vomiting, with epigastric pain, jaundice (the reason for the name ‘yellow fever’), multi-organ failure and haemorrhage. Bleeding can occur from the mouth, nose, eyes or stomach. 

20–25% of severe cases result in death 7 to 10 days after the onset of the toxic second phase. 

How is it transmitted?

In jungle or forest settings, YFV is transmitted from non-human primates (e.g. monkeys) to humans via mosquito bites. After a mosquito bites an infected monkey, it can transmit the virus to humans. 

In urban settings, YFV can be transmitted between humans via mosquito bites. After a mosquito bites an infected person, it can transmit the virus to other people. 

Aedes and Haemagogus mosquitoes are responsible for the transmission of YFV. They are day-biting and can breed around houses in urban settings and in forest or jungle settings. 

Epidemiology

Yellow fever occurs in the tropical and subtropical regions of Africa, the Caribbean and Central/South America. Disease risk depends on the time of year, duration of travel and degree of mosquito exposure. 

Prevention

Preventing mosquito bites with physical barriers is an important way of avoiding infection with YFV. Vaccines are also available to prevent disease. Vaccination is mandatory for travel to and from some areas. 

Physical barriers

Exposure to mosquito bites can be prevented in a number of ways, including: 

• wearing long, loose fitting clothes when outdoors 
• using mosquito repellents containing picaridin or DEET 
• limiting outdoor activity if there are lots of mosquitoes 
• using fly sprays, mosquito coils and plug-in repellent devices 
• sleeping under mosquito nets treated with insecticides if you don’t have flywire screens on your windows or are sleeping in an untreated tent/in the open outdoors.  

Vaccines

Stamaril is the only yellow fever vaccine registered for use in Australia. A single dose provides life-long protection. Yellow fever vaccination is not available on the National Immunisation Program (NIP) and is only to be administered in Australia as a travel vaccine by accredited yellow fever vaccination centres. 

Accredited yellow fever vaccination centres will provide vaccine recipients with an International Certificate of Vaccination or Prophylaxis as proof of vaccination. All travellers entering Australia who have been in a declared yellow fever infected country within 6 days of arrival to Australia must show proof of vaccination. If you are travelling to yellow fever infected countries, it is strongly recommended that you check the yellow fever entry requirements for all the countries you intend to enter, prior to travel. 

Prior infection with YFV will infer lifelong immunity. Infants born to immune mothers may have some immunity for up to 6 months. 

Vaccine precautions and contraindications

Stamaril is a live-attenuated vaccine and is contraindicated in those who are: 

• anaphylactic to a previous dose of Stamaril 
• anaphylactic to a component of Stamaril 
• allergic or anaphylactic to eggs^
• immunocompromised individuals 
• infants < 9 months of age
• have a history of thymus disorders
• pregnant women. ^ 

^Consider referral to a specialist immunisation clinic for individual discussion 

Precautions should be taken when considering immunisation of: 

• adults aged ≥ 60 years 
• breastfeeding women. 

Side effects

Side effects from yellow fever vaccination are usually mild and occur within the first 5 days of vaccination and can last up to 2 weeks. Symptoms can include headache, myalgia and fever. 

In some cases, yellow fever–vaccine associated neurotropic disease (YF-AND) can occur. It is a rare but serious adverse event following immunisation (AEFI). It includes diagnoses such as meningoencephalitis, Guillain–Barré syndrome, acute disseminated encephalomyelitis and bulbar palsy. 

Yellow fever–vaccine associated viscerotropic disease (YF-AVD) is rare and occurs in 3 to 4 cases per million doses of vaccine. It is characterised by multi-organ system failure and mimics natural yellow fever disease. Risk factors include older age and patients with a history of thymus disease. 

Any suspected AEFI should be reported to SAEFVIC. 

Resources

• DHHS: Yellow fever vaccination centres
• Australian Immunisation Handbook: Yellow fever
• Australian Government Department of Health and Aged Care: Yellow fever general fact sheet
• World Health Organization: Yellow fever