What is yellow fever?
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.
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.Yellow fever can be fatal. About eight people out of 100 who get yellow fever die from it.
Yellow fever symptoms
Typical
include:- high temperature (fever)
- nausea and vomiting
- muscle pain, including
- – yellowing of the skin and the whites of the eyes caused by liver damage
How yellow fever is spread
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.
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.Diagnosing yellow fever
Yellow fever is usually diagnosed based on the symptoms and a
.It's difficult to diagnose yellow fever based on the symptoms alone because they are often similar to those of other conditions, such as
and .Read more about
.Treating yellow fever
There is no specific antiviral treatment for yellow fever, but the symptoms can be treated.
Headache, high temperature and muscle pain can be treated using painkillers, such as
or . You should also drink plenty of fluids to avoid .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.
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.Yellow fever vaccination
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:
- laboratory workers who handle infected material
- anyone travelling to, or living in,
- anyone travelling to a country where an International Certificate of Vaccination or Prophylaxis (ICVP) against yellow fever is required for entry
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.Preventing mosquito bites
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:
- avoid places where mosquitoes live, such as swamps, forests and jungles
- choose air-conditioned accommodation
- choose accommodation with mesh screening over the windows and doors
- wear loose fitting, long-sleeved tops and trousers
- use insect repellent containing DEET on exposed skin
- burn a mosquito coil or use a plug-in device that releases insecticide
Yellow fever symptoms
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)
- nausea and vomiting
- muscle pain, including
- 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
- – a yellow tinge to the skin and whites of the eyes caused by liver damage
- 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.
Yellow fever 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 )
- whether you have been
- whether you are visiting jungle or forested areas
Yellow fever diagnosis
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:
- – a tropical disease that is spread by night-biting mosquitoes
- – a serious and potentially fatal bacterial infection
- viral – inflammation of the liver caused by a virus
- – a bacterial infection spread to humans by animals, such as rats
- – an infectious disease that, like yellow fever, is transmitted by the Aedes aegypti mosquito
Blood test
If you have yellow fever, a
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).
Treatment for yellow fever
There is no specific antiviral treatment for yellow fever. However, the symptoms can be treated.
A high temperature (fever),
and can be treated using painkillers, such as or .You should also drink plenty of fluids to avoid
.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 – of red blood cells to replace those lost through bleeding
- – where a machine is used to filter your blood if your kidneys are no longer working
Facts about yellow fever
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.
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.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
Risk areas in the Caribbean
In the Caribbean, there is a risk of getting yellow fever in Trinidad.
Preventing yellow fever
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.
Who should be vaccinated?
You should have the yellow fever vaccination if you are:
- a laboratory worker and handle infected material
- travelling to a country where you need an International Certificate of Vaccination or Prophylaxis (ICVP) before being allowed into the country – the certificate proves that you have been vaccinated against yellow fever
- travelling to, or living in, an area or country where yellow fever is found (see for a list of these countries)
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.
Where do I get vaccinated?
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.
Certificate of proof
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.
Seeking medical advice
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.
Who should not be vaccinated?
People who should not have the yellow fever vaccination include:
- babies under nine months of age – babies who are six to nine months old should only be vaccinated if the risk of getting yellow fever during travel is unavoidable
- pregnant women – unless the risk of yellow fever is unavoidable
- breastfeeding women – unless the risk of yellow fever is unavoidable
- people whose immune systems are lowered (immunosuppressed) – such as people with and those receiving or
- people who are allergic to eggs – the vaccine contains small amounts of egg
- people who have had a severe allergic reaction () to a previous dose of the yellow fever vaccine
- people who are allergic to any of the ingredients in the vaccine
- people who have a condition that affects the thymus gland (part of your immune system that is located in your upper chest)
- people who are currently very unwell (such as with a high fever) – this is to avoid confusing the diagnosis of your current illness with any side effects from the vaccine
- yellow fever naïve travellers – those who have not been previously exposed to the vaccine who are 60 years of age or over (unless the risk of yellow fever is unavoidable)
Exemption letters
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.
Side effects of the vaccine
After having the yellow fever vaccine, 10-30% of people will have mild side effects such as:
- muscle pain
- soreness at the injection site
- mild fever
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.
Yellow fever vaccine-associated neurological disease (YEL-AND)
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:
- a high temperature (fever) of 38ºC (100.4ºF) or above
- headache
- confusion
- problems with your nerves – for example, a problem with the nerves in your tongue that affects your ability to speak (focal neurological deficit)
- (a state of unconsciousness caused by injury or illness)
- (inflammation of the network of nerves that control the body's senses and movements)
Yellow fever vaccine-associated viscerotropic disease (YEL-AVD)
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:
- a high temperature (fever) of 38ºC (100.4ºF) or above
- headache
- muscle pain
- (inflammation of the liver)
- (low blood pressure)
- multiple organ failure