Primary Navigation for the CDC Website
CDC en EspaƱol

Yellow Fever Frequently Asked Questions

From Vaccine Recipients or Potential Recipients:

I think I got sick from the vaccine, what should I do?
Consult with your healthcare provider first.  Ask your healthcare provider to report your case to the Vaccine Adverse Events Reporting System (VAERS) if he or she thinks the vaccine has made you sick.

I just received the yellow fever vaccine.  Do I need to avoid contact with my immunocompromised family member?
There is no evidence that people who receive the vaccine shed live yellow fever virus that would be infectious to people who are immunocompromised. 

Does the yellow fever vaccine contain thimerosal?
The FDA-approved yellow fever vaccine does not contain thimerosal. 

Is the yellow fever vaccine recommended for people over age 60 traveling to yellow fever endemic areas?
Travelers over 60 years of age traveling to yellow fever endemic areas may be at increased risk for systemic adverse events following vaccination compared with younger persons.  Travelers aged >60 years should discuss with their physicians the risks and benefits of vaccination in the context of their destination-specific risk for exposure to yellow fever virus.  In addition to considering vaccination, travelers to endemic areas should protect themselves from yellow fever and other vector-borne diseases by using personal protective measures such as wearing clothes with long sleeves and long pants, using insect repellent containing DEET, and avoiding outdoor exposure during mosquito biting times.

How long should a woman wait to conceive after receiving a yellow fever immunization?
Although there is theoretical risk of adverse effects on pregnancy because yellow fever vaccine is a live virus vaccine, yellow fever vaccination has NOT been known to cause any birth defects when given to pregnant women. Yellow fever vaccine has been given to many pregnant women without any apparent adverse effects on the fetus. One case-control study of women vaccinated during pregnancy showed a slightly increased risk of spontaneous abortion. There is not likely to be any detectable live virus from vaccine in a recipient's bloodstream two weeks after vaccination. With some other live virus vaccines it is recommended to wait one month after vaccination before conceiving. While a two week delay between yellow fever vaccination and conception is probably fine, a one month delay has been advocated as a more conservative approach on purely theoretical grounds. If a woman is inadvertently or of necessity vaccinated during pregnancy she is unlikely to have any problems from the vaccine and her baby is very likely to be born healthy. Pregnant women may not develop adequate immune titers following yellow fever vaccination, but with vaccination preceding conception a pregnant woman should have a fine immune response.

From Students:

Where did yellow fever come from?
Yellow fever virus (YFV) has probably existed for thousands of years. It evolved in Africa from other, closely related viruses.

How did yellow fever get to the United States?
YFV was probably brought here in the 1500s by mosquitoes that "hitch-hiked" on ships sailing between Africa and America

Why is yellow fever not found in the United States presently? Has it not occurred in the past?
The last yellow fever epidemic in the United States occurred in New Orleans in 1905. 

Yellow fever is primarily transmitted by Aedes aegypti mosquitoes.  This particular type of mosquito is currently only found in the southern United States. For yellow fever to be introduced into the country, someone who is very recently infected with yellow fever has to visit or live in a location inhabited by Aedes aegypti mosquitoes.  Then, that person has to be bitten by an Aedes aegypti mosquito that then bites and infects another person. This would have to happen many times for an outbreak of yellow fever to occur.

Low occurrence of yellow fever world wide makes the introduction of yellow fever into the U.S. less likely. Additionally, many Americans are able to use preventative measures and secure their homes with tight fitting screens and air conditioning to prevent their exposure to mosquitoes. 

Why is there no treatment for the actual virus and just the symptoms?  
Viral infections are hard to treat. There are a few antiviral drugs, but none work very well against YFV. Perhaps someday there will be antiviral drugs that work against YFV.

Is yellow fever contagious?
Contagious means that something can be transmitted or passed directly from one person to another. YFV is only transferred from a person with YFV to another person by biting mosquitoes. Therefore, YFV is not "contagious" in the usual sense.

What does yellow fever actually do to your body?   
YFV multiplies in the blood stream and in certain organs, such as the liver, leading to tissue damage, especially in the liver. When the liver is damaged, lots of serious things happen, such as interference with blood-clotting mechanisms. Therefore, these patients often have uncontrolled bleeding from their intestinal lining, gums, nose, etc.

How did yellow fever get its name?
Infection with YFV can affect your liver and its normal functioning. People who are sick with yellow fever in this way may be jaundiced.  Jaundice is when excess yellow pigments (bilirubin) from a damaged liver color the skin, making a person look yellow. However, many other diseases that are not yellow fever also cause jaundice.

Did Walter Reed discover yellow fever?
The disease itself, yellow fever, was known for hundreds of years before Walter Reed was even born. He did not discover or "find" the disease. Reed's contribution (in the early 1900s) was to prove that yellow fever is transmitted to humans by mosquitoes.

What medicine is used to treat yellow fever?
There is no medicine that is particularly effective against the yellow fever virus itself. Patients with yellow fever are usually hospitalized so that doctors can treat the complications, such as bleeding and liver failure. Sometimes this works, sometimes it doesn't. Recovery from the virus infection itself depends on the person's immune system.  Their immune system must fight the virus and win. Sometimes it does, sometimes it doesn't.

Can you die from yellow fever?
Most persons with yellow fever recover. From 15% to 50% of patients with severe yellow fever disease die, usually within two weeks of illness.

How can I keep from getting yellow fever?
If you travel to a place where you can get yellow fever (South America or Africa) you prevent infection by getting vaccinated before you travel and by trying to avoid mosquito bites. 

Where can I get more information on the history of yellow fever?
More information is available from the following web sites:

CDC: Health Information for International Travel, 2005-2006

The University of Virginia: Yellow Fever and the Walter Reed Commission, 1898-1901

The University of Montana: Insects, Disease, and History

Page last modified: August 16, 2007
Content Source:
Division of Vector Borne Infectious Diseases
National Center for Zoonotic, Vector-Borne, and Enteric Diseases