Most people who get YF either have no symptoms or a mild illness and then fully recover. A small proportion of patients develop a severe illness with fever, jaundice (yellowing of the skin and eyes), bleeding and organ failure. The death rate is high in those who develop severe disease.

YF is a risk in some parts of Africa, 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.

YF is rare in international travellers. The most recent reported case in the UK was in 2018 in a traveller who had returned from Brazil. Prior to that, the last reported case in the UK was acquired by a laboratory technician working with the virus in London in the 1930s.

Between 1970 and 2015, eleven YF cases were reported in travellers from Europe and the United States who visited risk areas. From 2016 to 2018 an increase in travel associated cases was seen, mostly linked to outbreaks in Brazil and Angola. More than 35 unvaccinated travellers who were residents of non-endemic areas or countries (including at least 13 European travellers and one American traveller) contracted YF.

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