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Yellow Fever

What is Yellow Fever?

Yellow fever is a germ that is spread through mosquito bites. The yellow fever virus is found in tropical and subtropical areas of Africa and South America. For the most up-to-date information of where yellow fever in found, visit

How is yellow fever spread?

Yellow fever spreads to people by the bite of an infected Aedes or Haemagogus mosquito. Aedes mosquitoes are also capable of spreading dengue, chikungunya and zika. Mosquitoes get infected by feeding on an infected primate (human or non-human) and then can spread it to other primates. Infected people are infectious from shortly before the start of a fever and up to 5 days after the start of symptoms.

What are the symptoms?

Most people infected have mild or no symptoms. If symptoms do occur, they typically include: 
  • Sudden onset of fever
  • Chills
  • Severe headache
  • Back pain
  • General body aches
  • Nausea
  • Vomiting
  • Fatigue (feeling tired)
  • Weakness
Most people with the initial symptoms will get better within one week. Some people may continue to experience weakness and fatigue for several months. A few people will develop a more severe form of the disease. Severe symptoms include:
  • High fever
  • Yellow skin (jaundice)
  • Bleeding
  • Shock
  • Organ failure
Severe yellow fever disease can be deadly. Therefore, all people who develop symptoms of yellow fever after traveling to or living in an area at risk for the virus should see their healthcare provider. Once you have been infected, you are likely to be protected from future infections.

How long does it take for symptoms to appear?

Most people will not develop symptoms. For people who develop symptoms, the time from when they were bitten by an infected mosquito until symptom onset is typically 3 to 6 days.

How is yellow fever diagnosed?

Laboratory test can confirm the presence of the virus. If you have traveled to an area at risk for yellow fever and you have symptoms, talk to your healthcare provider right away.

How is yellow fever treated?

There is no medicine to treat or cure yellow fever. People infected should get plenty of rest, drink fluids to prevent dehydration, and take medication to reduce fever and pain. Aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs, such as ibuprofen or naproxen) should be avoided to reduce the risk of bleeding. People with severe symptoms should be hospitalized for close observation and supportive care.

Can yellow fever be prevented?

Yes. Get vaccinated and avoid mosquito bites! The vaccine is recommended for people aged 9 months and older traveling to or living in areas at risk for yellow fever virus. A single dose of the vaccine provides lifelong protection for most people. Yellow fever vaccine may be required for entry into certain countries. To view vaccination requirements and recommendations for specific countries, visit

Is the yellow fever vaccine safe?

Yes. The vaccine has been available for more than 80 years. The vaccine is a live, weakened form of the virus given as a single shot.

Who should NOT get the yellow fever vaccine?

Infants younger than 6 months of age should not get the vaccine. In addition, anyone with a severe allergy to any part of the vaccine, including eggs, chicken proteins, or gelatin should not get the vaccine. If you have any of the following conditions, talk to your healthcare provider to decide whether you can safely receive the vaccine:
  • HIV/AIDS or other disease that affects the immune system
  • Weakened immune system (due to cancer or other medical conditions, transplant, or drug treatment that affect immune function)
  • Thymus disorder
  • Adults 60 years of age and older
  • Infants 6 – 8 months of age
  • Pregnant women and nursing mothers.
Take the following steps to prevent mosquito bites:
  • The most important thing you can do is try to prevent mosquito bites while outdoors in an area with mosquitoes:
    • Use a mosquito repellent. Repellents approved by the EPA include those containing DEET, oil of lemon eucalyptus, Picaridin or IR3535. Read the directions on the product label to find out about precautions that need to be taken and how long the product is effective. 
      • Do not let children apply repellents to themselves.  Apply the repellent to your hands and rub it on the child. 
      • Do not apply repellents to children's eyes, mouth, or hands and use cautiously around ears.
      • Do not apply DEET on infants (mosquito netting can be used over infant carriers) or oil of lemon eucalyptus on children under 3 years of age.
    • When weather permits, wear protective clothing such as long-sleeved shirts, long pants, and socks.
    • Use air conditioning or window/door screens to keep mosquitoes outside. If needed, sleep under a mosquito bed net.

Boston Public Health Commission
1010 Massachusetts Ave, 6th Floor, Boston, MA 02118.
Phone:(617) 534-5395 Email: