What is Yellow Fever?
Updated: 3 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick Answer
What is yellow fever? Yellow fever is a mosquito-borne viral illness marked by fever, muscle pain and, in severe cases, jaundice (yellowing of the skin and eyes) and organ failure. It occurs mainly in sub-Saharan Africa and tropical South America. There is no specific antiviral treatment, so management is supportive, and prevention relies on vaccination and avoiding mosquito bites. [1]
What the research says
One dose gives near-complete early protection, but how long it lasts depends on age and immune status. In a meta-analysis of 36 studies from 20 countries (more than 17,000 participants aged 6 months to 85 years), pooled seroprotection after one dose was close to 100% by 3 months and stayed high in adults for 5 to 10 years. In children vaccinated before age 2 it was 52% within 5 years, and data indicated relevant waning in immunodeficient people (Kling et al., Clinical Infectious Diseases, 2022; DOI). [3]
Roughly 4 in 10 severe cases are fatal. A systematic review and meta-analysis of reported severe cases (fever with jaundice or haemorrhage) estimated a case fatality risk of 39% (95% CI 31–47%), higher in South America than in Africa, with high heterogeneity between studies (Servadio et al., BMC Infectious Diseases, 2021; DOI). [4]
Mass vaccination has reduced deaths. Modelling estimated 109,000 severe infections (95% CrI 67,000–173,000) and 51,000 deaths (95% CrI 31,000–82,000) in Africa and South America in 2018, and found that mass vaccination in Africa reduced deaths by 47% (95% CrI 10–77%) (Gaythorpe et al., eLife, 2021; DOI). [5]
Key Takeaways
Feature | Details |
Cause | Yellow fever virus |
Transmission | Bite of infected Aedes, Haemagogus or Sabethes mosquitoes |
Primary Regions | Tropical Africa and South America |
Incubation Period | 3 to 6 days after the bite |
Key Symptoms | Fever, headache, muscle aches, jaundice, bleeding |
Prevention | Vaccination (lifelong for most people), mosquito repellent, protective clothing |
Cure | None; supportive care only |
What is yellow fever?
Yellow fever is a viral hemorrhagic disease that affects humans and other primates. The “yellow” in its name refers to the jaundice that affects some patients, giving the skin and eyes a yellowish tint. It is a significant public health threat in specific regions: WHO estimates that 67,000–173,000 severe infections and 31,000–82,000 deaths occur each year in Africa and the Americas, with most of the burden in Africa.
How It Spreads
The virus is transmitted through the bite of infected mosquitoes, which become carriers after biting an infected primate (human or non-human). Unlike many common viruses, yellow fever does not spread between people through coughing, sneezing or kissing. An infected person can, however, pass the virus to a mosquito, which can then infect others.
Who Is at Risk?
The risk is highest for people living in or traveling to tropical and subtropical regions of:
Africa: particularly sub-Saharan regions.
South America: tropical areas, including the Amazon basin.
Travelers who have not been vaccinated are at significant risk when visiting these areas, especially if they spend time in forests or rural settings where the mosquito species that carry the virus are common.
What are the symptoms and stages of yellow fever?
Symptoms typically appear three to six days after the mosquito bite. Many people have no symptoms or only a mild illness, but the disease can progress in stages. [2]
Initial (Acute) Phase
The first stage usually lasts three to four days. Common symptoms include:
Remission Period
After the acute phase, most people improve and recover. For about 1 in 7 people who have initial symptoms, however, a brief remission lasting from a few hours to a day is followed by a much more dangerous stage. [2]
Toxic (Severe) Phase
In the toxic phase, the virus attacks multiple organ systems. This stage is characterized by:
Among people who develop severe disease, 30–60% die according to the CDC, while WHO puts the figure at about 50% within 7 to 10 days. [2] [1]
How is yellow fever diagnosed and managed?
If you develop a fever after traveling to a high-risk region, seek medical attention promptly.
How It Is Diagnosed
Diagnosis can be difficult, especially early on, because the first symptoms are nonspecific and can resemble malaria, dengue, hepatitis and other illnesses. Doctors rely on:
Travel history: recent visits to Africa or South America.
Symptom review: identifying the progression of fever and jaundice.
Blood tests: RT-PCR to detect the virus early in the illness, and antibody tests (such as ELISA) later. [1]
Treatment Options
There is no specific antiviral medication to cure yellow fever. Treatment is supportive, which means it focuses on managing symptoms and keeping the patient stable while the body fights the virus. [1]
Management Strategy | Description |
Rest | Essential for recovery and reducing strain on the body. |
Fluids | Increasing intake to prevent dehydration, especially during fever. |
Pain Relief | Acetaminophen (paracetamol) is generally used. Avoid aspirin and NSAIDs such as ibuprofen, which can raise the risk of bleeding. |
Hospitalization | Jaundice signals severe disease. Severe cases need hospital care, often intensive care, including support for liver and kidney failure. |
How does vaccination prevent yellow fever?
The most effective way to prevent yellow fever is vaccination. The vaccine is safe, affordable and highly effective. [1]
The Vaccine
Timing: get vaccinated at least 10 days before travel. Immunity develops in 80–100% of people within 10 days and in over 99% within 30 days. [1]
Duration: for most people, a single dose provides lifelong protection. Some groups, such as children vaccinated at a very young age or people with weakened immunity, may be advised to have a booster, so ask a travel clinic. [1] [3]
Requirements: some countries require proof of vaccination (the “Yellow Card”) for entry.
Who should not be vaccinated: infants under 9 months, pregnant women (except during outbreaks), people with severe egg allergy, and people with severe immunodeficiency or thymus disorders. [1]
Mosquito Avoidance
Even if you are vaccinated, reducing mosquito exposure protects you from other mosquito-borne diseases:
Repellent: use products containing DEET, picaridin or IR3535.
Clothing: wear long sleeves, long pants and socks, and treat clothing with permethrin.
Environment: stay in air-conditioned or well-screened rooms. Bed nets are less effective for yellow fever because the mosquitoes that spread it bite during the day.
Timing: be careful throughout the day, since these mosquitoes bite mainly in daylight.
Conclusion
Yellow fever remains a serious health threat in tropical regions, but it is highly preventable. By getting vaccinated at least 10 days before travel and taking careful mosquito precautions, you can explore these parts of the world more safely. If you are planning a trip, consult a travel clinic to make sure you are fully protected.
Frequently Asked Questions
What exactly is yellow fever?
A viral infection spread by mosquitoes that can cause fever, jaundice and organ failure.
Where is yellow fever most common?
In tropical regions of sub-Saharan Africa and South America.
How do you catch yellow fever?
From the bite of an infected Aedes, Haemagogus or Sabethes mosquito.
Is yellow fever contagious between people?
No. It does not spread through coughing, touching or kissing. An infected person can, however, pass the virus to mosquitoes, which can then infect others.
Can animals get yellow fever?
Yes. Primates such as monkeys are the main animal hosts and can die from the infection.
What are the early symptoms?
Sudden fever and chills, headache, back and muscle aches, nausea, vomiting, fatigue and weakness.
What is jaundice?
A yellowing of the skin and eyes caused by liver dysfunction.
Why is it called “yellow” fever?
Because of the jaundice (yellowing) that occurs in severe cases.
How long is the incubation period?
Symptoms usually appear 3 to 6 days after the bite.
Is there a cure for yellow fever?
There is no specific antiviral cure. Treatment is supportive.
How is it diagnosed?
Through travel history, symptoms and blood tests: RT-PCR early in the illness, and antibody tests later.
What should I do if I think I have it?
Seek medical care promptly and tell your provider when and where you travelled.
Can you survive yellow fever?
Yes. Most infected people have no symptoms or mild illness and recover completely. Among people who develop severe disease, 30–60% die, according to the CDC.
Who is at the highest risk?
Unvaccinated people who live in or travel to high-risk areas, especially forested or rural regions.
Is there a vaccine?
Yes. The yellow fever vaccine is safe, affordable and highly effective.
How many doses of the vaccine do I need?
For most people, one dose gives lifelong protection and no booster is needed. Some groups may be advised to have a booster, so ask a travel clinic.
When should I get the vaccine?
At least 10 days before travelling to a high-risk area. Immunity develops in 80–100% of people within 10 days and in over 99% within 30 days.
Are there side effects to the vaccine?
Side effects are rare. Mild reactions such as a sore arm or low fever can occur, and any serious reaction needs prompt medical attention.
Who should not get the vaccine?
Infants under 9 months, pregnant women (except during outbreaks), people with severe egg allergy, and people with severe immunodeficiency or thymus disorders. Above age 60, your provider will weigh the risks and benefits.
What is a “Yellow Card”?
The informal name for the International Certificate of Vaccination showing you have had the yellow fever vaccine. Some countries require it for entry.
How long does the vaccine take to work?
About 10 days to reach protective levels in most people, and over 99% are protected by 30 days.
Can I get yellow fever twice?
It is unlikely. Infection is believed to protect you against future infections.
Is yellow fever the same as malaria?
No. Malaria is caused by a parasite, while yellow fever is caused by a virus.
Do the same mosquitoes spread both?
No. Different mosquito species transmit each disease.
Is there a malaria vaccine?
Malaria vaccines exist, but they are different from the yellow fever vaccine and do not protect against it.
What are the “toxic phase” symptoms?
A return of high fever, jaundice, bleeding, organ failure and shock.
Can children get yellow fever?
Yes. People of all ages can be infected.
How common are deaths from yellow fever?
WHO estimates 31,000–82,000 deaths each year in Africa and the Americas, most of them in Africa.
What is “black vomit”?
Dark vomit caused by bleeding in the stomach during severe yellow fever.
Does yellow fever exist in the United States?
It does not circulate there. Cases are rare and imported by travelers, and the last major U.S. outbreak was in 1905.
Why did it disappear from the U.S.?
Largely because of improved mosquito control and sanitation.
Can mosquitoes in the U.S. carry it?
Mosquitoes that can carry the virus live in parts of the U.S., which is why imported cases are monitored, but the virus is not currently spreading there.
What is the best mosquito repellent?
Products containing DEET, picaridin or IR3535.
Should I wear specific clothing?
Yes. Long-sleeved shirts, long pants and socks, ideally treated with permethrin, help prevent bites.
Are mosquitoes active during the day?
Yes. The mosquitoes that spread yellow fever bite mainly during the day.
Do bed nets help?
They are less effective for yellow fever because the mosquitoes bite during the day. Screened or air-conditioned rooms and repellent are more useful.
What pain relievers are safe?
Acetaminophen (paracetamol) is generally used for fever and aches. Ask your provider before taking anything else.
Why avoid aspirin?
Aspirin and NSAIDs can raise the risk of bleeding.
How long does the acute phase last?
Usually 3 to 4 days.
What happens during the remission phase?
Symptoms briefly go away for a few hours to a day. Most people then recover, but about 1 in 7 people with initial symptoms go on to severe disease.
Is yellow fever found in cities?
Yes. Urban outbreaks can occur when infected people bring the virus into crowded areas where Aedes aegypti mosquitoes live.
What is “jungle yellow fever”?
The forest cycle, in which the virus circulates between monkeys and forest mosquitoes and occasionally infects people.
Can I travel without the vaccine?
Some countries require proof of vaccination for entry, and travelling unvaccinated to a risk area leaves you exposed. A travel clinic can advise you, including on medical exemptions.
Does the vaccine expire?
For most people a single dose is considered lifelong, with no booster needed. Some groups may be advised to have a booster.
What organs are most affected?
The liver and kidneys.
Can yellow fever cause shock?
Yes. Severe cases can lead to a dangerous drop in blood pressure and organ failure.
Is there a seasonal risk?
Mosquito numbers often rise in warm, wet conditions, so transmission can increase at those times.
How can communities prevent it?
Through mass vaccination, mosquito control such as removing standing water, and surveillance with rapid outbreak response.
Is yellow fever a global health concern?
Yes. WHO classes 27 African and 13 Latin American countries as high-risk for outbreaks, and international spread remains a concern.
Where can I get more information?
From the WHO and CDC yellow fever pages, a travel health clinic or your doctor.
References
World Health Organization. Yellow fever. WHO Fact Sheets. 20 October 2025. https://www.who.int/news-room/fact-sheets/detail/yellow-fever
Centers for Disease Control and Prevention. Symptoms of Yellow Fever. CDC Yellow Fever Virus. June 23, 2026. https://www.cdc.gov/yellow-fever/signs-symptoms/index.html
Kling K, Domingo C, Bogdan C, et al. Duration of protection after vaccination against yellow fever: a systematic review and meta-analysis. Clinical Infectious Diseases. 2022;75(12):2266-2274. PMID: 35856638. https://doi.org/10.1093/cid/ciac580
Servadio JL, Muñoz-Zanzi C, Convertino M. Estimating case fatality risk of severe yellow fever cases: systematic literature review and meta-analysis. BMC Infectious Diseases. 2021;21(1):819. PMID: 34399718. https://doi.org/10.1186/s12879-021-06535-4
Gaythorpe KAM, Hamlet A, Jean K, et al. The global burden of yellow fever. eLife. 2021;10:e64670. PMID: 33722340. https://doi.org/10.7554/eLife.64670
Disclaimer
The information provided in this article is for educational purposes only and is not intended as medical advice. Always seek the advice of a qualified healthcare provider with any questions you may have regarding a medical condition or travel vaccinations. Never disregard professional medical advice or delay in seeking it because of something you have read in this article.
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