Guidance

Yellow Fever: guidance, data and analysis

Travel and clinical advice on yellow fever including symptoms, diagnosis and epidemiology.

Epidemiology

Yellow fever is a viral disease that is transmitted by several species of mosquito. It is caused by the yellow fever virus, which belongs to the Flaviviridae family. It is endemic in tropical regions of Africa and South America where the World Health Organization (WHO) estimates approximately 200,000 cases occur each year, with 30,000 deaths.

Since January 2017, an outbreak of sylvatic (jungle) yellow fever has been ongoing in Brazil. The outbreak was first reported in December 2016 in the state of Minas Gerais, a known yellow fever risk area. Subsequently, confirmed cases were reported from the states of Rio de Janeiro, São Paulo and Espírito Santo (a state not previously considered at risk for yellow fever). Suspected cases have also been reported in a number of other states.

The number of cases and deaths reported so far in 2017 represents a significant increase compared to cases reported in previous years (nearly 400 confirmed cases compared to less than 10 confirmed each year in 2015 and 2016); further information is available from the Pan American Health Organization. This is the largest yellow fever outbreak ever reported in Brazil and the Brazilian Ministry of Health has launched extensive mass vaccination campaigns to complement routine yellow fever vaccination activities.

In response to this outbreak, WHO has extended the areas that are considered a risk for yellow fever transmission. All travellers to Brazil are advised to check the latest information regarding vaccine recommendations on the NaTHNaC Country Information Page for Brazil. Further updates about the outbreak and recommendations for travellers are available on the NaTHNaC website.

In 2016, a large yellow fever outbreak was reported in Angola and the Democratic Republic of Congo. Further details are available on the WHO website.

Transmission

Humans and monkeys are the principle reservoirs for the virus. The most common types of mosquito that transmit the yellow fever virus are Aedes spp (including Aedes aegypti), Haemagogus spp and Sabethes spp. Yellow fever does not naturally occur in the UK as the mosquitoes that transmit yellow fever are not established in the UK. The last known case to have occurred in the UK was in 1930 in a laboratory worker who had been working with yellow fever virus.

There are three main transmission cycles. Sporadic cases resulting from sylvatic (jungle) transmission are seen in South America and Africa. The intermediate cycle of transmission occurs in the moist savannah zones of Africa only, when semi-domestic mosquitoes infect both animals and humans and may cause small epidemics in rural villages. Urban transmission can occur where the virus is introduced into urban areas and the domestic Aedes aegypti mosquito is widespread. This can lead to large outbreaks if the virus is introduced into unvaccinated populations.

Symptoms

Yellow fever varies in severity. There are two stages to yellow fever; 3 to 6 days after infection symptoms may include fever, headache, nausea or vomiting, muscle pain (often with backache), and loss of appetite. Most people will make a full recovery after 3 to 4 days, however a small number (approximately 15%) will go on to develop jaundice, abdominal pain, renal failure and haemorrhage (bleeding). Up to half of those who develop the severe symptoms may die. Infection results in life long immunity in those who recover.

Diagnosis

Send the appropriate samples (with full clinical, travel and vaccination history including relevant dates) to PHE’s Rare and imported pathogens laboratory (RIPL). RIPL is a specialist centre for advice and diagnosis of a wide range of unusual viral and bacterial infections including yellow fever.

Prevention and advice for travellers

Yellow fever is rare in travellers. Between 1996 and 2017, 8 cases, of which 7 were fatal, have been recorded in (non-UK) European and US travellers. All cases were in unvaccinated travellers. Included in this total are 4 cases reported since August 2016 in unvaccinated EU citizens with recent history of travel to South America (2 Peru, 1 Bolivia, 1 Suriname). This re-emphasises the importance of vaccination and seeking advice before travel. The unusual increase in travel-associated cases over the past 6 months is consistent with an increased circulation of yellow fever virus in South America.

The yellow fever vaccine is very effective and safe, although there have been a few reports of rare adverse events associated with its use. One dose is considered to provide lifelong immunity in most travellers. Possession of an International Certificate of Vaccination or Prophylaxis (ICVP) for yellow fever vaccine is an entry requirement for some countries under the International Health Regulations (2005); yellow fever vaccine will also be recommended for those travelling to areas with a risk of disease transmission even if there is no certificate requirement. Further information is available on the National Travel Health Network and Centre (NaTHNaC) country pages including details of your nearest yellow fever vaccination centre.

Changes to yellow fever vaccination certificates

On 11 July 2016, changes were made to the IHR (2005) regarding the validity of the ICVP for yellow fever vaccine. The period of validity of the ICVP has changed from 10 years to the duration of the life of the person vaccinated. Certificates issued before 11 July 2016 are considered to be valid for life and should not be amended in any way. Further details are available from the NaTHNaC.

More information about yellow fever is available from NHS Choices, WHO, and NaTHNaC.

Information for Health Professionals

The NaTHNaC Yellow Fever Zone provides clinical and administrative resources for health professionals and other staff responsible for administering yellow fever vaccine and for those managing a YFVC.

See Yellow fever: the green book, chapter 35

Published 21 September 2016
Last updated 17 March 2017 + show all updates
  1. Updated Brazilian outbreak information.
  2. Updated with information about outbreak in Brazil and links to specific travel advice.
  3. Added Information for health professionals
  4. First published.