Yellow Fever Vaccine

Yellow fever is a disease caused by a virus spread by infected mosquitoes. It is found in tropical and subtropical areas of Africa and South America. It is a very rare cause of illness in U.S. travelers, but it can be severe.

If you are planning international travel to an area at risk for yellow fever, vaccination can help protect you, and some countries require proof of vaccination for entry. Understanding how yellow fever spreads, recognizing its symptoms, and knowing who should and shouldn’t be vaccinated can help you prepare.

What Is Yellow Fever?

Yellow fever is a viral infection spread to people mainly through the bite of infected Aedes and Haemagogus mosquitoes. Mosquitoes become infected by feeding on infected monkeys or people. Most infected people have no symptoms or mild symptoms and recover completely, but some develop severe, life-threatening illness.

How Does Yellow Fever Spread?

Yellow fever spreads primarily through mosquito bites. It does not spread from person to person through coughing, sneezing, or touching. The virus moves through three transmission cycles:

• Jungle (sylvatic): The virus spreads between mosquitoes and monkeys in the tropical rain forest. People get it when bitten by infected mosquitoes, usually while visiting or working in the jungle in Africa or South America.
• Intermediate (savannah): This cycle occurs in Africa. The virus spreads from mosquitoes to people living or working in jungle border areas.
• Urban: The virus spreads from person to person through mosquitoes, primarily Aedes aegypti, which prefer to live near and bite people. It is usually brought into a city by an infected person who caught it in the jungle or savannah.

What Are the Symptoms of Yellow Fever?

Symptoms usually start 3 to 6 days after infection and come on suddenly. They can include:

• Fever and chills
• Severe headache
• Back pain and general body aches
• Nausea or vomiting
• Fatigue and weakness

Most people who develop symptoms improve within a week. For about 1 in 7 people with initial symptoms, a brief period of feeling better is followed by severe disease, including:

• High fever
• Jaundice (yellowing of the skin and eyes)
• Bleeding
• Shock
• Organ failure

There is no specific treatment for yellow fever. Care is supportive, including rest, fluids, and over-the-counter pain relievers. Avoid aspirin and other NSAIDs, such as ibuprofen and naproxen, because they may increase the risk of bleeding. Anyone with yellow fever should also protect themselves from mosquito bites for up to 5 days after symptoms begin, so mosquitoes can’t pick up the virus and spread it to others. Anyone who develops symptoms after traveling to an at-risk area should see a healthcare provider promptly and say when and where they traveled.

Who Should Get the Yellow Fever Vaccine?

Yellow fever vaccine is recommended for people aged 9 months and older who are traveling to or living in at-risk areas of South America and Africa. Because serious reactions can occur, CDC advises vaccinating only people who are at risk of exposure or who need proof of vaccination to enter a country. Check your destination on the CDC Travelers’ Health page.

When Should You Get the Yellow Fever Vaccine?

Plan your vaccination before departure. CDC recommends seeing a healthcare provider or travel clinic 4 to 6 weeks before any international trip. WHO reports that immunity develops in 80% to 100% of people within 10 days and in over 99% within 30 days.

• Single dose: The vaccine is a live, weakened virus. For most travelers, one dose provides long-lasting protection.
• Booster doses: Additional doses may be considered for women who were pregnant when first vaccinated, people who had a stem cell transplant after their last dose, people with HIV, and laboratory workers who handle wild-type yellow fever virus. They are also considered for travelers vaccinated at least 10 years ago who will be in a higher-risk setting based on season, location, activities, and length of travel.
• Proof of vaccination: A completed International Certificate of Vaccination or Prophylaxis is now valid for the lifetime of the person vaccinated.

Who Should Not Get the Yellow Fever Vaccine?

The vaccine is not recommended for people with:

• An allergy to a vaccine component, such as eggs
• An age younger than 6 months
• Symptomatic HIV infection, or a CD4+ T-lymphocyte count below 200/mm³ (below 15% of total lymphocytes in children younger than 6)
• A thymus disorder associated with abnormal immune function, or a primary immunodeficiency
• A malignant neoplasm or a transplant
• Immunosuppressive or immunomodulatory therapy

Talk to a provider first if you are 60 or older, pregnant, breastfeeding, or have asymptomatic HIV with CD4+ 200 to 499/mm³.

What Are the Side Effects?

Reactions are generally mild and include headaches, muscle aches, and low-grade fevers. Rare but serious events include life-threatening allergic reactions, nervous system disease, and disease affecting internal organs. Be sure to talk to your healthcare provider if you have any concerns prior to vaccination, or if you develop symptoms after vaccination.

Other Ways to Prevent Yellow Fever

Vaccination should be combined with mosquito bite prevention. Yellow fever mosquitoes are primarily day-biting, but CDC notes that mosquitoes bite during both day and night. To reduce your risk:

• Use an EPA-registered insect repellent with DEET, picaridin, oil of lemon eucalyptus, para-menthane-diol (PMD), or 2-undecanone, and follow the label directions.
• Wear loose-fitting, long-sleeved shirts and long pants.
• Treat clothing and gear with 0.5% permethrin.
• Choose lodging with air conditioning or screens on windows and doors, and use a mosquito net if you are sleeping outside or no screened room is available.

These precautions remain important even after vaccination.

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