Yellow Fever

What is yellow fever?
Yellow fever is caused by infection with yellow fever virus. It is one of the most lethal viral diseases. It is spread to humans from the bite of infected mosquitoes. 

What are the signs and symptoms of yellow fever?
Yellow fever varies in severity. The time from infection with the virus to showing symptoms ranges from 3 to 6 days. The most common early symptoms include:

  • muscle aches
  • high temperature
  • headache
  • loss of appetite
  • nausea and vomiting 

Within 3-4 days after the start of symptoms, many patients will have an improvement in symptoms and a gradual recovery.

However, 15-25% of patients progress to a more serious illness within 24 hours of seeming to recover. There may be bleeding from the mouth, eyes, ears and stomach, yellow coloured skin (this is how the disease got its name) and kidney damage. The patient develops very low blood pressure and kidneys, liver and heart begin to fail. Twenty to 50% of patients who develop this form of the disease die within 7-10 days after the start of symptoms.

People who recover from yellow fever will not catch it again. Infection with the virus gives lifelong protection in those who recover. 

How is yellow fever spread?
Yellow fever virus is spread to humans from the bite of infected mosquitoes. Infected female mosquitoes of Aedes or Haemogogus species (South America only) can spread the virus.

These types of mosquito are active during daylight hours and bite from early sunrise to sunset. Once infected with the virus, the mosquito remains infectious for life (2-3 months). The mosquito is killed by extremes of heat and cold but the virus can survive from season to season in mosquito eggs. This makes eradication of the disease difficult. 

How is yellow fever diagnosed?

Yellow fever is diagnosed in a patient who travelled to an affected area (such as travel to parts of Africa or South America) using a sample of their blood.

What is the treatment for yellow fever?
There is no specific medicine for yellow fever. Supportive nursing care and treatment of symptoms are the standard. 

How is yellow fever prevented?
Vaccination is the most reliable way to prevent yellow fever. A highly effective vaccine has been available for more than 50 years. One dose of yellow fever vaccine is enough to give protection for life against yellow fever. Booster doses of the vaccine are not needed. The vaccine provides protection within 30 days for 99% of persons vaccinated.  

As well as preventing illness in people, vaccination also prevents spreading the disease further to other countries. Some countries require proof of vaccination from travelers passing through from affected areas. Failure to produce a certificate may result in the traveler being placed in quarantine. 

Vaccination against yellow fever is recommended for the following groups:

  • Those travelling to, passing through or living in an affected area
  • Those travelling to any country that requires an International Certificate of Vaccination or Prophylaxis for entry
  • Those handling potentially infectious materials (e.g. laboratory staff)  

People who are usually not recommended yellow fever vaccination are:

  • babies under nine months of age
  • pregnant and breastfeeding women
  • people over the age of 60
  • people with weakened immune systems – such as those with HIV
  • people who are very allergic to any of the ingredients in the vaccine – including people with an egg allergy  

It is also important to avoid mosquito bites as they can spread yellow fever and other infectious diseases. Information on protecting yourself against biting mosquitoes is available on

What countries/areas are affected by yellow fever?
Yellow fever occurs in tropical regions of Africa and in parts of South America. Unvaccinated travellers to these areas are at risk of infection and illness. To date yellow fever has not appeared in Asia or the Pacific region. 

A list of affected areas is available on the website of the Centers for Disease Control and Prevention (CDC) in the United States. Information on recent outbreaks of yellow fever can be accessed on the WHO website. It is important to check this information prior to any trips, as the situation could change rapidly. 

What is the current travel advice?
Although ongoing cases and outbreaks of yellow fever are occurring in Africa and South America, the disease is preventable by vaccination. There has been only 1 documented case of yellow fever in a vaccinated traveller. This nonfatal case occurred in a traveller from Europe who visited several West African countries in 1988. 

The Department of Foreign Affairs and Trade (DFA) provides advice to travellers that is updated regularly. Please consult the DFA website and click on the relevant country. It is important to check this information prior to any trips, as the situation could change rapidly. 

What should I do if I am travelling to an area affected by yellow fever?

  • All travellers going to an area affected by yellow fever should take measures to prevent infection with the virus with appropriate vaccination and mosquito avoidance.
  • Irish citizens who live in affected areas should also take measures to prevent infection with the virus with appropriate vaccination and mosquito avoidance.
  • People showing symptoms suggestive of yellow fever infection after returning from an affected area should contact their healthcare provider. 

What do I do if I’m living/working in an area where yellow fever virus is circulating?
If you become ill you should contact your local health care provider who will be able to advise on your individual circumstances. 

What do I do if I’m returning to Ireland from an area where yellow fever is circulating?
If you become ill upon your return to Ireland, you should contact your doctor for assessment and let him/her know of your recent travel history to an affected area

Have cases of yellow fever been diagnosed in Ireland?
Yellow fever has been diagnosed in small numbers of unvaccinated travelers returning to Ireland from affected areas. No cases of yellow fever have been reported in vaccinated travelers returning to Ireland from an affected area to date. 

Yellow fever infection is a notifiable disease in Ireland under the Infectious Diseases Regulations. All medical practitioners and laboratories are legally required to report cases of yellow fever infection to the Medical Officer of Health. Further information on reporting cases is available at: 

Last updated: 04/07/2018