Rapid risk assessment: Outbreak of yellow fever in Angola, 24 March 2016

Risk assessment
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European Centre for Disease Prevention and Control. Outbreak of yellow fever in Angola – 24 March 2016, Stockholm, 2016.

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​The current epidemic of yellow fever in Angola highlights the risk of infection for unvaccinated travellers, and the risk of further international spread through introduction of the virus into areas with a competent vector and susceptible populations. Yellow fever, an acute viral haemorrhagic vector-borne disease, has recently been identified among returning travellers to China, Kenya, Mauritania and the Democratic Republic of Congo.

This document assesses the risk of yellow fever infections in Europe related to the ongoing outbreak of yellow fever in Angola, and the notification of imported cases in China and possibly Mauritania.

Executive summary

ECDC risk assessment of the advancing epidemic of yellow fever in Angola and the related imported cases highlights the risk of infection for unvaccinated travellers.

There is also a risk of further international spread through introduction of the virus into areas with a competent mosquito vector and susceptible human populations.

However, the risk of importation of the virus to the EU by returning travellers is limited because EU citizens are most likely to get vaccinated before travelling.

Outbreak in Angola

An outbreak of yellow fever is ongoing in Angola since December 2015, with 1 132 suspected and confirmed cases reported, including 168 deaths. Imported cases were identified among returning travellers from Angola in China, Kenya, the Democratic Republic of Congo (DRC) and Mauritania. A rapid increase in the number of cases and provinces affected has been recorded since mid-January 2016.

Information to travellers

Vaccination against yellow fever is recommended for all those ≥9 months old travelling to areas with yellow fever virus transmission. 
The yellow fever vaccine is recommended for travellers to all countries/areas listed in the WHO list of countries and areas with yellow fever vaccination requirements and recommendations. This list includes Angola.

Risk of international spread

The evolution of the epidemic situation in Angola is of concern. Viraemic patients travelling to areas where suitable vectors and susceptible human populations are present pose a risk for establishment of local transmission.
Establishment of local transmission is possible in areas where Aedes aegypti mosquito is present. Local transmission cannot be excluded also in areas where Aedes albopictus is abundant, even though it is not confirmed that this mosquito species is a competent vector for yellow fever.

What’s risk to the EU:

  • Risk of importation to the EUThe risk of importation of yellow fever in Europe is limited, as EU travellers coming from affected areas are likely to have been immunised. The risk is thus limited to unvaccinated viraemic travellers from epidemic areas.
  • Risk of spread in the EUThe risk of establishment of yellow fever in the EU/EEA is mainly related to areas where Aedes aegypti is present, such as some of the Overseas Countries and Territories (OCT) and Outermost Regions (OMR) of the EU, as well as in the Black Sea region of Europe (See ECDC maps on distribution of invasive mosquitoes in Europe).

The competence of European Aedes albopictus mosquito populations needs to be further assessed, but areas where this mosquito species is active should be considered as potential areas for local transmission of yellow fever, if the virus is introduced through a viraemic traveller.

Prevention of importation and spread in the EU

Countries with receptive areas for yellow fever transmission (presence of the active suitable mosquitoes and naïve population for yellow fever) should consider stipulating the requirement of a yellow fever vaccination certificate for travellers coming from affected areas during the mosquito season.

Yellow fever is an acute viral haemorrhagic vector-borne disease, which can be transmitted by the Aedes mosquitoes. It is endemic in countries in Africa and South America. Most infections in humans are either asymptomatic or result in mild illness; around 15% of the infected persons develop the severe form of the disease, with bleeding and multi-organ failure, and up to up to 50% of those may die. Yellow fever can be prevented by vaccination.