Yellow fever (YF) is a vaccine preventable viral infection transmitted predominantly by certain species of day biting mosquitoes. YF virus can cause an illness that results in jaundice (yellowing of the skin and eyes) and bleeding, with severe damage to the major organs. The death rate is high in those who develop severe disease.

YF is a risk in parts of the tropical and sub-tropical regions of Africa and South and Central America and in Trinidad (Caribbean). Areas with a risk of YF transmission are countries (or areas within countries) where mosquito species known to transmit the disease are present and where the infection is reported in monkeys and/or humans.

Yellow fever is rare in western travellers. The last reported case in the UK was acquired by a laboratory technician working with the virus in London in the 1930s.

On 14 March 2017 the European Centre for Disease Prevention and Control reported that, since August 2016, a total of four cases of YF have been reported in European travellers who visited YF risk regions in South America. Prior to these cases, between 1970 and 2015 a total of ten YF cases were reported in unvaccinated travellers from Europe and the United States who visited South America or West Africa.

The risk of contracting YF is determined by the following factors:

• Travel destination.
• Intensity of YF transmission in the area to be visited.
• Season of travel (most cases in travellers have occurred in the late rainy season to early dry season).
• Duration of travel.
• Activities allowing exposure to mosquitoes.
• Immunisation status.

In order to prevent the international spread of YF, under International Health Regulations, countries may require proof of vaccination, recorded in an International Certificate of Vaccination or Prophylaxis (ICVP). Country specific certificate requirements can be found in our Country Information pages.

Prevention

Those visiting YF risk areas should practise meticulous mosquito bite avoidance.

Yellow fever vaccine

A highly effective live YF vaccine is available and in general vaccination is recommended for all persons visiting countries where there is a risk of YF virus transmission. Very rarely yellow fever vaccination is associated with serious adverse reactions. Prior to vaccination a careful risk assessment is required that takes into account:

• risk of disease to the individual
• certificate requirements for vaccination according to international health regulations
• risk of complications following vaccination

Vaccine schedule

A four week minimum interval period should be observed between the administration of yellow fever and measles, mumps and rubella vaccines (MMR). Co-administration of these two vaccines can lead to sub-optimal antibody responses to yellow fever, mumps and rubella antigens. Where protection is required rapidly then the vaccines should be given at any interval; Public Health England guidance states an additional dose of MMR should be considered.  

Contraindications 

YF vaccine should not be given to the following:

• Infants less than six months.
• Persons with a confirmed anaphylactic reaction to a previous dose of YF vaccine.
• Persons with a confirmed anaphylactic reaction to any of the components of the vaccine.
• Persons with a confirmed anaphylactic reaction to egg.
• Persons who are immunocompromised due to a congenital condition, disease process or treatment.
• Persons with a history of a thymus disorder or thymectomy*.

*To date there is no evidence of increased risk of yellow fever vaccine–associated serious adverse events in people who have undergone incidental surgical removal of their thymus (e.g. during cardiac surgery) or have had indirect radiation therapy in the distant past. People who had incidental removal of their thymus after the age of one year may therefore receive a yellow fever vaccine following a detailed risk assessment. A cautious approach is recommended for those who had incidental removal of their thymus before the age of one year. In these cases further advice should be sought.

Precautions

For those with a febrile illness (fever) or who are acutely unwell, YF vaccination should be postponed until full recovery.

Where travel to YF risk areas is unavoidable, YF vaccination may be considered for the following groups (expert opinion may be advisable, see resources below for details on adverse events):

• Breast feeding women
• Infants age six to eight months
• Individuals age 60 years and older
• HIV-infected individuals (with a CD4 count greater than 200 and a suppressed viral load, specialist advice should be sought)
• Pregnant women

Length of protection

With some exceptions, protection from YF vaccination lasts for at least 35 years, and could be life-long. Reinforcing immunisation (booster dose) should be offered to a small subset of travellers who may be at continued risk see Public Health England guidance. 

As of 11 July 2016, The World Health Organization states that the period of validity of the yellow fever certificate (ICVP) has changed from 10 years to the duration of the life of the person vaccinated. This applies to all ICVPs for yellow fever vaccination, including certificates already issued, and new or duplicate certificates. 

Individual country certificate requirements should be checked on our Country Information pages.

Resources

• More detailed information can be found in our Yellow fever factsheet.
• Public Health England: Immunisation against infectious disease. Yellow fever.
• Further details on yellow fever vaccine can be found on the Summary of Product Characteristics (SPC) on the electronic Medicines Compendium
• Yellow fever information leaflet for travellers