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Yellow fever is a serious viral infection that's usually spread by a type of mosquito known as the Aedes aegypti mosquito. It can be prevented with a vaccination (see below).
Yellow fever mainly occurs in sub-Saharan Africa (countries to the south of the Sahara desert), South America and in parts of the Caribbean.
There have not been any recent cases of yellow fever in North America, Europe or Asia. Since 1996, six travellers from Europe and North America have died from the infection. None of them were vaccinated.
Read more about the risk areas for yellow fever.
Yellow fever can be fatal. About eight people out of 100 who get yellow fever die from it.
Typical symptoms of yellow fever include:
Yellow fever is a type of virus known as a flavivirus. The virus is transmitted through mosquito bites. It can be spread from one host to another, usually between monkeys, or from monkeys to humans, or from person to person. The mosquitoes live and breed in jungle and urban areas.
Read more about how yellow fever is transmitted.
Yellow fever is usually diagnosed based on the symptoms and a blood test.
Read more about diagnosing yellow fever.
There is no specific antiviral treatment for yellow fever, but the symptoms can be treated.
If your symptoms are severe, you may be admitted to hospital so that your condition can be monitored and you can receive supportive nursing care.
Read more about treating yellow fever.
There is a vaccination for yellow fever. Some countries require proof of vaccination (a certificate) against yellow fever before they let you enter the country.
You should have a yellow fever vaccination at least 10 days before your travel. This will allow enough time for your body to develop protection against the yellow fever infection.
The yellow fever vaccination is recommended for:
Read more about the yellow fever vaccination.
As well as getting the yellow fever vaccination before travelling, you should also take steps to avoid being bitten by mosquitoes.
The mosquitoes that carry yellow fever bite during daylight hours. Although it may not always be possible, you should try to:
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.
The symptoms of the first stage, also known as the 'acute phase', include:
Most people improve after three to four days and their symptoms disappear. However, some people go on to develop more serious symptoms.
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:
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.
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.
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.
If you are travelling, your risk of getting yellow fever will depend on:
Yellow fever is usually diagnosed based on the symptoms and the results of a blood test.
It can sometimes be difficult to diagnose yellow fever based on the symptoms alone because they are often similar to those of other conditions such as:
If you have yellow fever, a blood test will be able to detect the presence of special proteins called antibodies, which are produced by the body to fight the virus.
The blood test may also show a reduction in the number of infection-fighting white blood cells (leukopenia). This can occur because the yellow fever virus affects your bone marrow (the spongy material at the centre of some bones that produces blood cells).
There is no specific antiviral treatment for yellow fever. However, the symptoms can be treated.
You should also drink plenty of fluids to avoid dehydration.
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:
Vaccination is the most effective way of preventing yellow fever.
There are yellow fever vaccinations. A single dose of the yellow fever vaccine will protect against yellow fever for at least 10 years. It is recommended that you have a booster dose every 10 years if you are still at risk of infection.
You should have the yellow fever vaccination if you are:
You must have a yellow fever vaccination at least 10 days before you travel. This will allow enough time for your body to develop protection against the yellow fever infection.
Your certificate will only become valid 10 days after you have the yellow fever vaccination.
Yellow fever vaccinations can only be given at designated and registered centres. For a centre to become a designated yellow fever vaccination centre, it must register with the appropriate authority.
Under regulations set out by the World Health Organization (WHO), anyone travelling to a country or area where the Aedes aegypti mosquito is found must have an International Certificate of Vaccination or Prophylaxis (ICVP).
If you have been travelling in an "at-risk" area during the past month, it is a good idea to carry your certificate with you. This will help avoid potential problems with immigration. It is possible for travellers without a valid yellow fever vaccination certificate to be vaccinated and held in isolation for up to 10 days. An ICVP is not required for entry into the UK.
If you lose your certificate, you may be able to get another one reissued as long as you have details of the vaccination batch number and the date you had the vaccination.
Always consult staff at a designated vaccination centre if you are planning to travel to an area where there is a risk of getting yellow fever. If you tell them where you are travelling to, they will be able to advise you about whether you need to be vaccinated against yellow fever and whether you need an ICVP.
People who should not have the yellow fever vaccination include:
In cases where having a yellow fever vaccination is not advised, your doctor may be able to issue you with an exemption letter. The letter should be written on headed notepaper and include the practice details. It may be accepted by some immigration authorities.
If you are travelling from an area where there is a risk of yellow fever without a valid yellow fever certificate, immigration officials are legally entitled to quarantine you for a period of at least seven days at the point of arrival into a country.
After having the yellow fever vaccine, 10-30% of people will have mild side effects such as:
Reactions at the injection site usually occur one to five days after being vaccinated, although other side effects may last for up to two weeks.
An allergic reaction to the vaccine occurs in one case out of every 130,000 doses of the vaccine that are given.
Rarely, the yellow fever vaccine is associated with a neurological condition known as yellow fever vaccine-associated neurological disease (YEL-AND). Neurological means that it affects the nerves and the nervous system, including the brain and spinal cord.
YEL-AND occurs in around four cases out of every 1 million doses given. However, for people who are 60 years of age or over and yellow fever vaccine naïve, the incidence of YEL-AND increases to around one in every 50,000. This represents the highest risk for any vaccine currently in use.
The symptoms of YEL-AND include:
The yellow fever vaccine is also associated with yellow fever vaccine-associated viscerotropic disease (YEL-AVD). Viscerotropic means that it affects the viscera – your internal organs, such as the heart or lungs.
YEL-AVD occurs in around three cases out of every 1 million vaccines that are given. However, for people who are 60 years of age or over and yellow fever vaccine naïve, the incidence of YEL-AVD increases to just over one in every 50,000. This represents the highest risk for any vaccine currently in use.
Symptoms of YEL-AVD include:
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.
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:
The areas of South America where there is a risk of getting yellow fever are:
In the Caribbean, there is a risk of getting yellow fever in Trinidad.
Important: Our website provides useful information but is not a substitute for medical advice. You should always seek the advice of your doctor when making decisions about your health.