Yellow Fever: The Disease & Vaccine
Yellow fever is an old disease. Cases have been documented since the mid-1600s. The vaccine against yellow fever is also among our older vaccines. The first yellow fever vaccine was developed in the mid-1930s; it was a live, weakened vaccine, called 17D. The vaccine won its developer, Max Theiler, the Nobel Prize in Physiology and Medicine in 1951. His work remains the basis for today’s yellow fever vaccines. Modern-day concerns around yellow fever center on two areas. First, more people are at risk as the virus spreads to new areas because of climate change and globalization, meaning more people living closer to and interacting with each other and with animals. Second, in most places community vaccination rates are not sufficient to stem spread of the disease where many people coexist. The vaccine has some severe side effects, yet it also suffers from periods in which the supply is insufficient. For these reasons, new yellow fever vaccines are being developed.
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The disease
What is yellow fever?
Yellow fever is a virus that causes two main health issues:
- Hepatitis (inflammation of the liver)
- Hemorrhaging (severe bleeding problems)
The bleeding and severe liver damage caused by yellow fever virus kills 1 of every 5 people infected with the virus.
Symptoms of yellow fever can include:
- Fever
- Chills
- Muscle pain
- Headache
- Jaundice, or yellowing of the skin
Every year there are up to 175,000 severe cases of yellow fever causing between 30,000 and 80,000 deaths worldwide. About 20 to 60 of every 100 people who get yellow fever die from their infection. Most infections and deaths occur in Africa and South America. To learn more about risk of yellow fever transmission relative to your travel destination, consult the World Health Organization list of countries.
How can you catch yellow fever?
Infected mosquitoes spread yellow fever. In cities and other populated areas, spread between mosquitoes and people is common and leads to the largest numbers of cases.
In less populated settings, such as jungles and African savannahs, the disease can still spread to people, but it also spreads to monkeys. As such, in these areas, fewer cases occur in people, but the disease continues to be a concern because of ongoing transmission between mosquitoes and monkeys.
How can you avoid yellow fever?
The best way to avoid yellow fever is to avoid being bitten by a mosquito. Mosquitoes often feed between dusk and dawn, so try to remain indoors during these times. You should also:
- Use mosquito netting over the bed
- Wear long-sleeved shirts and long pants
- Wear insect repellents with DEET on exposed skin
- Wear clothing treated with an insecticide, such as permethrin
Yellow Fever Q&A
Yellow Fever Special Topics Q&A
Infectious Disease and Travel Q&A
Infectious Disease and Travel Special Topics Q&A
The vaccine
How is the yellow fever vaccine made?
The yellow fever vaccine is made by growing yellow fever virus in mouse embryo cells and in chick embryo cells. The final preparation of the vaccine is made in eggs. Growing yellow fever virus in mouse and chick cells over and over again weakened it. So, when this live, weakened virus is injected, a protective immune response develops without causing illness.
Newer versions of the yellow fever vaccine are in clinical trials. Some use different approaches than the live, weakened virus. But, recently, a second live, weakened version was tested in a phase II clinical trial. The newer vaccine uses a version of the virus that has genetic changes, seemingly preserving the vaccine’s ability to cause immunity but decreasing the likelihood for side effects. This vaccine will still need to be further tested in phase III clinical trials before it would be considered for licensure in the U.S.
Who should receive the yellow fever vaccine?
The yellow fever vaccine is required for entry into many countries in Africa and South America. The vaccine is also used in countries where yellow fever occurs, but in these cases, the vaccine is recommended, not required, for entry. The vaccine is given as a single shot to anyone older than 9 months of age.
Some groups of people should not receive the yellow fever vaccine, including:
- Pregnant women
- Anyone with a weakened immune system, such as people with AIDS or those receiving chemotherapy or immune suppressive therapy.
- Infants younger than 6 months of age
- Anyone with severe allergies to eggs, egg products, chicken proteins or gelatin
Does the yellow fever vaccine have side effects?
Minor side effects occur in fewer than 1 in 20 people and can include:
- Mild headaches
- Muscle aches
- Low-grade fevers
Severe side effects can also occur, but they are rare:
- Severe allergic reaction – A reaction in which the person develops hives, has difficulty breathing, or experiences a sudden drop in blood pressure. This reaction occurs in less than 1 per 1 million people.)
- Viscerotropic disease – A disease that resembles yellow fever. This adverse reaction can on rare occasions be fatal. Most often it occurs in adults more than 65 years of age. However, when traveling to a country where yellow fever is common, the benefits of the yellow fever vaccine still outweigh this rare, but severe, risk since about 20-60 of every 100 people who get yellow fever disease die from it.
Because of the potential for severe allergic reactions, people should stay at the location where they were vaccinated for at least 15 minutes after receiving the vaccine.
Other questions you might have
What is the youngest age that a child could receive the yellow fever vaccine?
The yellow fever vaccine is recommended for anyone older than 9 months of age. However, the vaccine can be given to those as young as 6 months for travel in rural areas, small towns or villages with a high risk for yellow fever. When the vaccine is required for entry, sometimes the lower age requirement varies, so it is helpful to speak with a travel medicine expert about your child’s risk and need for the vaccine prior to travel.
Relative risks and benefits
Do the benefits of the yellow fever vaccine outweigh its risks?
Every year thousands of people in the world catch yellow fever and about 1 in every 5 die from the disease. Travelers from the U.S. to countries where yellow fever occurs can (and do) get yellow fever, and there are no specific treatments. On the other hand, the yellow fever vaccine has only rare serious side effects. Whereas about 1of every 1 million people will experience a serious side effect from yellow fever vaccine, about 2 to 6 of every 10 people with the disease will die from their infection. Therefore, for those traveling to countries where yellow fever is common, the benefits of the yellow fever vaccine outweigh its risks.
Also, remember that the vaccine is not required for entry to some countries where the disease is common. The decision to get the vaccine should be based on whether you are traveling to a country where the disease is common, and not on whether the vaccine is required. (See the “Vaccine consideration for travelers” page to find a list of websites that contain the most recent information on vaccines for travel).
Disease risks
- Hepatitis (inflammation of the liver)
- Hemorrhaging (severe bleeding)
- Fever, chills, muscle pain, headache and jaundice (yellowing of the skin)
- Death from severe bleeding and liver damage (1 of 5 people)
Vaccine risks
- Mild headaches, muscle aches or low-grade fevers (1 in 20 people)
- Severe allergic reaction (1 in 1 million people)
- Viscerotropic disease (1 in 1 million people)
Reference
Orenstein WA, Offit PA, Edwards KM, and Plotkin SA. Smallpox and vaccinia in Plotkin’s Vaccines, 8th Edition, 2024, 1251-1321.
Reviewed by Paul A. Offit, MD, on April 28, 2026