Rapid risk assessment: Outbreak of yellow fever in Brazil, Second update

Risk assessment

European Centre for Disease Prevention and Control. Outbreak of yellow fever in Brazil, Second update – 18 January 2018. Stockholm: ECDC; 2018. 

This is the second update of a rapid risk assessment originally produced on 25 January 2017 and updated on 13 April 2017. It assesses the risk to EU/EEA countries and citizens associated with the ongoing outbreak of yellow fever in Brazil. It was triggered by the evolution of the epidemic in São Paulo state and reports of an imported case into the EU/EEA from Brazil.

Executive summary


The 2016/2017 yellow fever outbreak in Brazil was declared over in September 2017, yet the upsurge of human cases since December 2017 and non-human primate epizootics since September 2017 indicate a resurgence of yellow fever virus circulation in Brazil, particularly in São Paulo state.  

The detection of non-human primate cases in the vicinity of the metropolitan regions of São Paulo and Rio de Janeiro is of concern, particularly in light of the start of the mosquito activity season in December 2017 and the suboptimal vaccination coverage in some areas. There is an increased likelihood of peri-urban or urban cycles of yellow fever transmission, which significantly increases the number of potentially exposed people.

The Carnival, one of the largest international mass gatherings in Brazil, will take place from 9 to 14 February 2018. During the Carnival, the number of EU/EEA travellers to Brazil is expected to increase, hence the number of travel-related cases among unvaccinated travellers may increase in the coming month.

The risk of yellow fever importation and subsequent transmission in the continental EU/EEA is currently very low because the virus has to be introduced by viraemic travellers in an area with an established, competent and active mosquito vector population. 

Options for response

Advice to travellers

EU/EEA citizens who travel to, or live in, areas at risk of yellow fever in Brazil and other countries in South America are advised to:

  • check their vaccination status and get vaccinated if necessary, in accordance with national and WHO recommendations. Vaccination against yellow fever is recommended for people visiting or living in yellow fever risk areas, from nine months of age and without contraindication. An individual risk–benefit analysis should be conducted by professionals in tropical or travel medicine prior to vaccination, taking into account the period, destination, duration of travel and likelihood of being bitten by mosquitoes as well as individual risk factors for adverse events following yellow fever vaccination;  
  • take measures to prevent mosquito bites indoors and outdoors, especially between sunrise and sunset when mosquito vectors are most active. These measures include:
    • the use of mosquito repellent in accordance with the instructions indicated on the product label;
    • wearing long-sleeved shirts and long trousers;
    • sleeping or resting in screened/air-conditioned rooms or using mosquito nets at night and during the day.

International travellers returning from affected areas may be requested to show proof of yellow fever vaccination (or a contraindication certificate) when entering countries or territories infested with Aedes aegypti mosquitoes.  Vaccination requirements and recommendations for international travellers are available from the World Health Organization’s website. 

Advice to health professionals

Physicians, health professionals and travel health clinics should be provided with, or have access to, regularly updated information on areas with ongoing yellow fever transmission and should consider yellow fever in the differential diagnoses for illnesses in relation to unvaccinated travellers returning from at risk areas.  

To reduce the risk of adverse events following immunisation, healthcare practitioners responsible for yellow fever vaccinations should be aware of the contraindications and follow the manufacturers’ advice on precautions before administering yellow fever vaccine.  

Option for the EU Overseas Countries and Territories and Outermost Regions with presence of Aedes aegypti

In the EU Overseas Countries and Territories and Outermost Regions where Aedes aegypti is established or has been introduced, yellow fever vaccination checks should be considered for travellers coming from Brazil in order to reduce the risk of yellow fever importation.

Options for the safety of substances of human origin (SoHO)

Deferral of blood donors returning from areas affected by malaria will be sufficient to prevent most yellow fever infectious donations. In addition, precautionary deferral of non-vaccinated blood donors is suggested for 28 days after returning from an area affected by yellow fever but non-endemic for malaria. Potential blood donors should be deferred from donation for two weeks after live virus immunisation with the yellow fever 17D vaccine.

For organs, tissues and cells, the risk of yellow fever transmission from a donor who may have visited an affected area should be balanced with the likelihood of virus transmission. If an organ donor has received yellow fever vaccine during the four weeks before donation, an individual risk assessment of the immune status of all prospective recipients is mandatory. Yellow fever vaccination is contraindicated for immunocompromised patients after solid organ and haematopoietic stem cell transplantation. Potential transplant patients living in countries endemic for yellow fever or planning travel to endemic countries should be immunised before transplantation.

There are no specific criteria for the deferral of a prospective SoHO donor with a history of yellow fever. Therefore, it is suggested that a general recommendation be applied that donors must have recovered, be afebrile and asymptomatic on the day of donation and may donate SoHO 14 days after full recovery.