Yellow fever is a potentially fatal disease caused by the yellow fever virus.

The virus is found in parts of South America and Africa. It’s spread through the bite of mosquitos infected with the virus. It’s not transmitted from person to person.

Some people with yellow fever only experience flu-like symptoms and recover completely after a short time. Others develop a more severe form of the infection that causes serious symptoms, such as:

  • high fever
  • vomiting
  • yellow skin (jaundice)

According to the Centers for Disease Control and Prevention (CDC), 30 to 60 percent of those who develop a severe case of yellow fever die.

There’s no cure for yellow fever, though some treatments can help to reduce symptoms. There’s also a yellow fever vaccine that protects people against the yellow fever virus.

We explain how the vaccine works, how it’s given, and its potential side effects.

The yellow fever vaccine causes your immune system to produce antibodies against the virus. It’s administered as a relatively painless injection.

If you’re in the United States and are planning to travel to an area where yellow fever is common, you’ll need to get vaccinated at an authorized yellow fever vaccination center.

You can find their locations here.

Originally, a single dose was meant to last for at least 10 years. But in 2013, the World Health Organization (WHO) announced that a single injection should provide life-long immunity.

Keep in mind that this change still isn’t reflected in the International Health Regulations, a legally-binding document put out by WHO. As a result, some countries may not accept a certificate that’s more than 10 years old.

You can check regulations in specific countries here. You might want to call the local embassy before your trip just to be sure.

As with almost any other medicine or vaccine, some people have a reaction to the yellow fever vaccine.

Usually, this reaction is mild, with side effects such as:

  • fever
  • muscle aches
  • mild joint pain

In addition, any kind of injection can cause soreness, redness, or swelling around the injection site.

These side effects usually begin shortly after the injection and can last up to 14 days, though most resolve within one week. About 1 in 4 people who get the vaccine experience mild side effects.

There’s a small risk of serious side effects from the yellow fever vaccine. The CDC states that this includes:

  • a severe allergic reaction, which affects about 1 in 55,000 people
  • a severe nervous system reaction, which affects about 1 in 125,000 people
  • severe illness with organ failure, which affects about 1 in 250,000

After receiving the vaccine, keep an eye out for these symptoms of a serious allergic reaction:

  • behavior changes
  • hives
  • trouble breathing
  • high fever
  • swelling of the face, tongue, or throat
  • dizziness
  • weakness

Seek emergency treatment if you experience any of these within minutes or hours of getting the vaccine.

Other symptoms that warrant an immediate visit to a doctor include:

  • confusion
  • cough
  • difficulty swallowing
  • irritability
  • itching
  • nervousness
  • rapid heartbeat
  • rash
  • severe headache
  • stiff neck
  • throbbing in the ears
  • tingling
  • vomiting

Yellow fever vaccine is recommended for the following:

  • all persons aged 9 months or older who are living in or traveling to areas of South America, Africa, or other countries where the yellow fever virus is found
  • people who are traveling to countries requiring proof of yellow fever immunization
  • anyone who might come into contact with the yellow fever virus, such as laboratory workers or healthcare professionals

People who are pregnant are advised to get the vaccine only if they must travel to an area where there’s an epidemic and protection from mosquito bites isn’t possible.

The vaccine shouldn’t be given to:

  • children younger than 9 months of age
  • adults older than 59 years of age
  • people with reduced immunity, such as people with HIV or those receiving chemotherapy
  • people who’ve had a severe reaction to egg, gelatin, or other ingredients of the vaccine
  • people who’ve had a severe allergic reaction to a previous dose of the vaccine
  • people who’ve had their thymus removed or those with a thymus disorder
  • travelers over the age of 60 who haven’t been previously vaccinated against yellow fever

If you have a fever, it’s best to wait to get the vaccine until you’re feeling better.

In addition, those who are pregnant or breastfeeding should only be vaccinated if there’s an unavoidable risk or protection against mosquito bites isn’t possible.

Yellow fever is a serious illness, so it’s important to get vaccinated if you plan to be in an area where the virus is common.

If you’re not sure if you should get the vaccine, talk to a doctor. They can help you weigh the benefits and risks.

Keep in mind that the vaccine isn’t foolproof. When traveling to areas with the yellow fever virus, it’s important to still protect yourself against mosquito bites by using nets, insect repellants, and protective clothing.

Try to stay indoors during peak times when mosquitos may bite to further lower your risk. Most species bite from dusk to dawn, but one species feeds during the daytime. Staying in air-conditioned rooms can lower your risk.