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| Yellow fever is a mosquito-borne viral disease that can be prevented through vaccination and mosquito control. |
Yellow fever is a potentially severe viral disease transmitted to humans through the bite of infected mosquitoes. It occurs mainly in tropical areas of Africa and Central and South America.
Some infected people experience no symptoms, while others develop fever, headache, muscle pain, nausea and weakness. A smaller proportion develop severe disease involving jaundice, bleeding, shock and organ failure.
Yellow fever remains an important public-health threat because outbreaks can spread rapidly in communities with low vaccination coverage. However, the disease is preventable. A single dose of the yellow fever vaccine provides lifelong protection for most people.
What Is Yellow Fever?
Yellow fever is an acute viral haemorrhagic disease caused by the yellow fever virus, a member of the Flaviviridae family.
The name “yellow fever” comes from the jaundice that can occur in people with severe infection. Jaundice causes the skin and the whites of the eyes to appear yellow because the liver has been affected.
Yellow fever is spread mainly through infected mosquitoes. It is not normally transmitted directly from one person to another through touching, coughing, sneezing, sharing food or ordinary social contact.
History of Yellow Fever
Yellow fever is believed to have originated in Africa and was probably introduced into the Americas through ships involved in transatlantic trade, including the slave trade.
Large outbreaks occurred in the Americas from the seventeenth century onward. One of the most devastating epidemics occurred in Philadelphia in 1793, killing thousands of people and forcing many residents to flee the city. New Orleans also experienced repeated outbreaks, including a major epidemic in 1905.
For centuries, people did not understand how yellow fever spread. Contaminated air, clothing and personal contact were wrongly blamed.
A major breakthrough came in 1881 when Cuban physician Dr Carlos Juan Finlay proposed that mosquitoes transmitted yellow fever. His theory was later confirmed through research conducted by the Yellow Fever Commission led by Walter Reed around the beginning of the twentieth century.
The discovery made mosquito control a central part of yellow fever prevention.
Another major advancement came in the 1930s when Max Theiler and his colleagues developed the 17D yellow fever vaccine. The vaccine became one of the most successful vaccines ever developed. Theiler received the 1951 Nobel Prize in Physiology or Medicine for his discoveries concerning yellow fever and its control.
Where Is Yellow Fever Found?
Yellow fever occurs mainly in tropical parts of:
Sub-Saharan Africa
Central America
South America
The disease is endemic in several countries, meaning that the virus continues to circulate and can cause outbreaks when vaccination coverage falls or infected mosquitoes increase.
Nigeria is one of the African countries at risk of yellow fever transmission. Vaccination is therefore included in the country’s routine childhood immunisation programme.
Yellow fever does not currently occur naturally in Asia, despite the presence of mosquitoes capable of carrying the virus. Preventing the international spread of the disease remains an important reason some countries require travellers to show proof of vaccination.
How Yellow Fever Is Transmitted
Yellow fever is transmitted when a mosquito bites an infected human or non-human primate and later bites another person.
Different transmission cycles can occur.
Sylvatic or jungle transmission
In forest environments, mosquitoes transmit the virus between monkeys. Humans who enter the forest may become infected when bitten by an infected mosquito.
Intermediate transmission
This form occurs mainly in parts of Africa. Mosquitoes living around both forest and village environments transmit the virus between monkeys and humans. It can produce outbreaks in several neighbouring communities.
Urban transmission
Urban transmission occurs when an infected person introduces the virus into a densely populated area where Aedes aegypti mosquitoes are present.
The mosquitoes bite infected people, acquire the virus and transmit it to other residents. Low vaccination coverage and poor mosquito control can allow a major urban outbreak to develop.
Yellow Fever Incubation Period
The incubation period is usually between three and six days after the bite of an infected mosquito.
This means that a person may feel well for several days before symptoms begin.
Signs and Symptoms of Yellow Fever
Many yellow fever infections cause no symptoms or only mild illness.
When symptoms occur, they commonly include:
Sudden fever
Severe headache
Chills
Muscle pain, particularly back pain
General body weakness
Loss of appetite
Nausea
Vomiting
Sensitivity to light
Dizziness
Most people who develop mild illness begin to improve within several days.
Severe or Toxic Yellow Fever
A small proportion of symptomatic patients temporarily improve and then enter a more dangerous toxic phase.
Signs of severe yellow fever may include:
High fever
Yellowing of the skin or eyes
Severe abdominal pain
Persistent vomiting
Bleeding from the nose, mouth or gastrointestinal tract
Blood in vomit or stool
Reduced urine production
Kidney problems
Liver failure
Confusion
Seizures
Shock
About 15% of people who develop symptoms progress to severe disease. Among patients who enter the toxic phase, approximately half may die within seven to ten days.
Anyone who develops fever together with jaundice, unusual bleeding, severe weakness or persistent vomiting should be taken to a health facility immediately.
Diagnosis of Yellow Fever
Yellow fever can be difficult to diagnose from symptoms alone.
Early symptoms may resemble several other infections, including:
Malaria
Dengue fever
Lassa fever
Viral hepatitis
Leptospirosis
Typhoid fever
Other viral haemorrhagic fevers
Healthcare workers consider the patient’s symptoms, vaccination history, recent travel, place of residence and possible exposure to mosquitoes.
Laboratory tests may include:
Reverse-transcription polymerase chain reaction
RT-PCR can detect the genetic material of the yellow fever virus, especially during the early stage of infection.
Antibody testing
Blood tests can detect antibodies produced in response to the virus. These may include immunoglobulin M testing and neutralisation tests.
Results must be interpreted carefully because antibodies produced after yellow fever vaccination or infection with related viruses may affect some tests.
Suspected cases should be reported and investigated through the appropriate public-health surveillance system.
Treatment of Yellow Fever
There is currently no specific antiviral medicine that cures yellow fever.
Treatment is supportive and aims to help the body function while the immune system fights the infection.
Supportive care may include:
Rest
Adequate fluids
Oral or intravenous rehydration
Oxygen when needed
Treatment of low blood pressure
Management of liver or kidney complications
Blood products when clinically necessary
Treatment of secondary bacterial infections when confirmed
People with severe symptoms should be admitted to a hospital for close observation and appropriate treatment.
Medicines to avoid
Aspirin and non-steroidal anti-inflammatory medicines such as ibuprofen and naproxen should generally be avoided in suspected yellow fever because they may increase the risk of bleeding.
Paracetamol may sometimes be used to control fever and pain, but it should be taken only at the recommended dose and preferably following advice from a healthcare professional, particularly when liver injury is suspected.
Antibiotics do not kill the yellow fever virus. They should only be used when prescribed for a confirmed or suspected bacterial infection.
How to Prevent Yellow Fever
Yellow fever can be prevented through vaccination, mosquito control and personal protection.
1. Receive the yellow fever vaccine
Vaccination is the most effective way to prevent yellow fever.
WHO states that a single dose provides lifelong protection for most people. Routine booster doses every ten years are no longer required under international health regulations.
In Nigeria, the vaccine is included in the routine childhood immunisation schedule and is normally given at nine months of age. Parents should check their child’s vaccination record and visit a primary healthcare centre when a dose has been missed.
Parents can also read AnjKreb’s guide to the immunisation schedule in Nigeria to understand when important childhood vaccines are given.
2. Prevent mosquito bites
Vaccinated and unvaccinated people should still take steps to avoid mosquito bites.
Useful measures include:
Sleeping under an insecticide-treated mosquito net
Wearing long-sleeved shirts and long trousers
Applying an approved mosquito repellent
Installing screens on windows and doors
Using air conditioning where available
Closing doors and windows that do not have screens
Avoiding unnecessary exposure in heavily mosquito-infested places
Unlike many malaria-carrying mosquitoes that are most active at night, Aedes aegypti mosquitoes commonly bite during the daytime. Protection is therefore needed throughout the day.
3. Eliminate mosquito breeding sites
Aedes mosquitoes often breed in small collections of stagnant water around homes.
Communities can reduce mosquito populations by:
Emptying water from buckets, tyres and containers
Covering water-storage tanks
Cleaning gutters and drains
Disposing of containers that collect rainwater
Changing water in flower containers regularly
Keeping the surrounding environment clean
Supporting organised mosquito-control activities
4. Protect infected people from further mosquito bites
During the first few days of infection, mosquitoes may acquire the virus after biting an infected person.
A suspected or confirmed patient should therefore remain under a mosquito net or in a screened room, particularly during the early stage of illness. This helps prevent mosquitoes from carrying the virus to other people.
Yellow Fever Vaccination and the Yellow Card
International travellers may be required to present an International Certificate of Vaccination or Prophylaxis, commonly called the yellow card.
The vaccination certificate generally becomes valid ten days after a person receives their first yellow fever vaccine. Under the International Health Regulations, a properly issued certificate remains valid for the life of the vaccinated person.
Travellers should confirm the current requirements for their destination and any countries through which they will transit.
A vaccination requirement for entry is not always the same as a medical recommendation. A country may require proof of vaccination to prevent imported cases even when the traveller’s immediate destination has little or no risk of transmission.
Who Should Seek Medical Advice Before Vaccination?
Although the yellow fever vaccine is safe and highly effective, it is a live vaccine and may not be suitable for everyone.
Medical advice is particularly important for:
Babies younger than nine months
Pregnant women
Breastfeeding women
Adults aged 60 years or older receiving their first dose
People with severe egg allergy
People with a weakened immune system
People receiving chemotherapy or strong immune-suppressing medicines
People with certain thymus disorders
People who previously experienced a serious reaction to the vaccine
The decision should be based on the person’s medical condition, likelihood of exposure and travel requirements. WHO generally does not recommend the vaccine for infants under nine months, pregnant women outside outbreak situations, people with severe egg allergy, or people with severe immunodeficiency or thymus disorders.
When to Seek Urgent Medical Care
Seek immediate medical attention when a person living in or returning from a yellow fever risk area develops:
Fever and yellow eyes
Persistent vomiting
Unusual bleeding
Severe abdominal pain
Confusion
Difficulty staying awake
Reduced urination
Breathing difficulty
Convulsions
Severe weakness or collapse
Tell the healthcare worker about recent travel, vaccination history and possible mosquito exposure.
Do not attempt to diagnose yellow fever at home. Malaria, Lassa fever, dengue and other serious infections may cause similar symptoms and also require urgent investigation.
Frequently Asked Questions
Is yellow fever contagious from person to person?
Yellow fever is not normally spread directly through touching, coughing, sneezing or sharing food. It is transmitted mainly when infected mosquitoes bite people.
Can yellow fever be cured?
There is no specific medicine that cures the infection. Early supportive care can improve the patient’s chance of recovery and help manage complications.
Does one yellow fever vaccine last for life?
For most people, yes. WHO states that one dose provides lifelong protection and a routine booster is not required.
Can a vaccinated person still get yellow fever?
The vaccine is highly effective, but no vaccine protects every person in every circumstance. Vaccinated people should continue taking precautions against mosquito bites.
Can children receive the vaccine?
Yes. Yellow fever vaccination is generally recommended from nine months of age in countries where the disease is a risk. In Nigeria, it is part of routine childhood immunisation.
Can yellow fever occur more than once?
People who recover from yellow fever generally develop long-lasting immunity. Vaccination also provides lifelong protection for most recipients.
Is yellow fever the same as malaria?
No. Both are transmitted by mosquitoes, but they are caused by different organisms. Yellow fever is caused by a virus, while malaria is caused by Plasmodium parasites. They also require different diagnostic tests, treatment and prevention strategies.
Conclusion
Yellow fever has caused devastating epidemics throughout history, but it is now largely preventable.
The most effective protection is vaccination. A single dose provides lifelong immunity for most people. Mosquito-control activities, environmental sanitation, early reporting and prompt medical care are also essential.
People living in Nigeria and other countries where yellow fever occurs should ensure that eligible family members are vaccinated. Travellers should check their vaccination status and destination requirements before departure.
Fever accompanied by yellowing of the eyes, vomiting, bleeding or severe weakness should never be ignored. The affected person should be taken to a qualified health facility immediately.
Last fact-checked and updated: July 2026
Medical Disclaimer
This article is provided for general health education and does not replace diagnosis, treatment or advice from a qualified healthcare professional. Seek medical care for suspected yellow fever or any severe or worsening symptoms.
Author Bio
Adeyinka Joseph Alonge is a public health professional, researcher and writer with interests spanning health, science, technology, personal development and practical knowledge for everyday life.
Sources and Further Reading
World Health Organization: Yellow fever fact sheet
World Health Organization: Yellow fever vaccine information
Nigeria Centre for Disease Control and Prevention: Yellow fever frequently asked questions
United States Centers for Disease Control and Prevention: Yellow fever symptoms, diagnosis, treatment and prevention
Nobel Prize: Max Theiler and the development of the yellow fever vaccine
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