Yellow Fever

Yellow fever is a serious viral infection that's spread by certain types of mosquito. It’s mainly found in sub-Saharan Africa, South America and parts of the Caribbean.

The condition can be prevented with a vaccination and is a very rare cause of illness in travellers.

Six travellers from Europe and North America have died from yellow fever since 1996. None of them were vaccinated.

If you're planning to visit places where yellow fever infection is found, you should seek travel health advice about the vaccination available. A map and list of countries where yellow fever is found is available on the NHS Fit for Travel website.

How yellow fever is spread

The virus that causes yellow fever is passed to humans through the bites of infected mosquitoes. The mosquitoes that spread the infection are usually active and bite during daylight hours, from dusk until dawn, and are found in both urban and rural areas.

Yellow fever can’t be passed directly from person to person through close contact.

Yellow fever symptoms

The symptoms of yellow fever occur in two stages. The initial symptoms develop three to six days after infection, and can include:

• a high temperature (fever)
• a headache
• nausea or vomiting
• muscle pain, including backache 
• loss of appetite

This stage will usually pass after three to four days and most people will make a full recovery.

However, around 15% of people go on to develop more serious problems, including jaundice (yellowing of the skin and whites of the eyes), kidney failure and bleeding from the mouth, nose, eyes or stomach (causing blood in your vomit and stools).

Up to half of those who experience these symptoms will die.

After being infected with yellow fever, it usually takes three to six days for the symptoms to appear. This is known as the incubation period.

The symptoms of yellow fever can occur in two distinct stages.

First stage

The symptoms of the first stage, also known as the 'acute phase', include:

• a high temperature (fever) of 38ºC (100.4ºF) or above
• chills (shivers)
• headache
• nausea and vomiting
• muscle pain, including backache 
• loss of appetite

Most people improve after three to four days and their symptoms disappear. However, some people go on to develop more serious symptoms.

Second stage

After the initial symptoms of yellow fever, around 15% of people develop more severe symptoms. This is sometimes referred to as the 'toxic phase'. The symptoms can include: 

• a recurrent fever 
• abdominal pain
• vomiting
• jaundice – a yellow tinge to the skin and whites of the eyes caused by liver damage
• kidney failure 
• bleeding from the mouth, nose, eyes or stomach, leading to blood in your vomit and stools (faeces)

Half of those who progress to the second, toxic phase of yellow fever die within 10-14 days. The other half recover with no major organ damage and are immune from the condition for the rest of their life.

Overall, this means about seven or eight people out of every 100 who develop yellow fever will die from it.

Causes

Yellow fever is caused by a type of virus known as a flavivirus. The infection is transmitted by the bite of certain mosquitoes.

Yellow fever cannot be spread by close contact between two people.

How yellow fever is spread 

The Aedes aegypti mosquito usually spreads yellow fever in urban and some rural areas. However, in forested areas, other types of mosquito may also carry the virus. The mosquitoes usually bite during daylight hours.

The mosquito becomes infected by biting a monkey or human who is already infected with the virus. Infected mosquitoes can then pass the disease on to other monkeys or humans that they bite. Once infected, a mosquito is a source of infection throughout its life.

The virus is thought to be widespread among monkeys that live in the jungle canopy (the tree tops) of some parts of Africa and the Americas.

Occasionally, an infected mosquito will pass the virus on to a person in the jungle, such as a forestry worker, who may then become a source of infection when they return to their community.

The risk of an urban yellow fever outbreak is highest in areas close to jungles where the mosquitoes and infected monkeys live.

Am I at risk?

If you are travelling, your risk of getting yellow fever will depend on:

• where you are travelling to and whether there is currently an outbreak of yellow fever in the area (see risk areas for yellow fever)
• whether you have been vaccinated for yellow fever
• whether you are visiting jungle or forested areas

Risk Areas

The World Health Organization (WHO) keeps an up-to-date list of the countries and regions where there is an increased risk of yellow fever.

Although the number of yellow fever cases in some countries may be low, visitors may still be at risk of infection. For example, low rates of yellow fever could be due to a vaccination programme in the area. However, there may still be a risk of unvaccinated visitors becoming infected.

Read more about the yellow fever vaccination.

Risk areas in Africa

Most cases of yellow fever occur in sub-Saharan Africa (the countries and regions south of the Sahara desert). In the past, other areas of Africa have also been affected by outbreaks of urban yellow fever.

The areas of Africa where there is a risk of getting yellow fever are:

• Angola
• Benin
• Burkina Faso
• Burundi
• Cameroon
• Central African Republic
• Chad
• Congo
• Ivory Coast (Côte d’Ivoire)
• Democratic Republic of the Congo
• Equatorial Guinea
• Ethiopia
• Gabon
• Gambia
• Ghana
• Guinea
• Guinea Bissau
• Kenya
• Liberia
• Mali
• Mauritania
• Niger
• Nigeria
• Rwanda
• Senegal
• Sierra Leone
• South Sudan 
• Sudan 
• Togo
• Uganda

Risk areas in South America

The areas of South America where there is a risk of getting yellow fever are: 

• Bolivia
• Brazil
• Colombia
• Ecuador
• French Guiana
• Guyana
• Panama
• Paraguay
• Peru
• Suriname
• Venezuela

See the Fit for Travel website for maps showing the yellow fever risk areas in Africa and South America.

Risk areas in the Caribbean

In the Caribbean, there is a risk of getting yellow fever in Trinidad.

When to seek medical advice

You should see a doctor as soon as possible if you develop symptoms of yellow fever and are currently travelling in an area where the virus is found, or have recently returned from one of these areas.

Yellow fever is usually diagnosed based on the symptoms and the results of a blood test.

Treating yellow fever

There is no specific treatment for yellow fever, but the symptoms can be treated while your body fights off the virus.

Headache, high temperature and muscle pain can be treated using painkillers such as paracetamol or ibuprofen. You should also drink plenty of fluids to avoid dehydration.

If your symptoms are particularly severe, you may be admitted to hospital so that your condition can be monitored and you can receive supportive care.

There is no specific antiviral treatment for yellow fever. However, the symptoms can be treated.

A high temperature (fever), headaches and back pain  can be treated using painkillers, such as paracetamol or ibuprofen.  

You should also drink plenty of fluids to avoid dehydration.

Hospital treatment 

If your yellow fever symptoms are severe, you may be admitted to hospital so you can be monitored and receive supportive nursing care. Additional treatment may be necessary, including:

• a ventilator to help you breathe
• a blood transfusion – of red blood cells to replace those lost through bleeding
• dialysis – where a machine is used to filter your blood if your kidneys are no longer working

Yellow fever vaccination

The vaccination against yellow fever should be given at least 10 days before travelling to an area where the infection is found, to allow your body to develop protection against the virus that causes the infection.

Some countries require a proof of vaccination certificate before they will let you enter the country. This will only become valid 10 days after you are vaccinated.

The yellow fever vaccination is given as a single injection and it offers protection to over 95% of those who have it.

The protection offered by the vaccine may be life-long, but vaccination certificates are currently only valid for 10 years, and a booster dose may sometimes be needed after this time if you are planning another visit to an area where yellow fever is found.

Even if you have been vaccinated, it’s still a good idea to take steps to prevent mosquito bites while you’re travelling – for example, by using mosquito nets, wearing loose, long-sleeved clothing, and applying insect repellent containing 50% DEET to exposed skin.