The World Health Organization has issued an alert regarding an extensive outbreak of yellow fever (YF), initially identified in Angola at the end of December 2015 and confirmed by Institut Pasteur Dakar in mid-January 2016. There followed a rapid increase in the number of cases of YF in a number of countries:
- More than 2,400 suspected cases have been identified in Angola, resulting in 298 deaths, despite extensive local vaccination campaigns. The outbreak was officially declared on April 23rd, 2016.
- In addition, three countries have reported cases of YF imported from Angola, these being:
This rapidly spreading outbreak has highlighted the risk of international spread through non-immunised travellers. A small cluster of cases of YF in Uganda, identified in April, does not appear to be related to the Angolan outbreak.
The situation is complicated by the fact that the virus in Angola and DRC is largely concentrated in major urban areas. The risk of spread and local transmission to other provinces in Angola, DRC and Uganda remains a serious concern. The risk is high also for potential spread to bordering countries especially those classified as low risks for yellow fever disease (i.e. Namibia, Zambia) where the population, travellers and foreign workers are not vaccinated against yellow fever.
Following a visit to the worst affected areas by the Director-General of WHO, Dr Margaret Chan, an Emergency Committee to consider the risk posed by YF was convened by the Director General under the International Health Regulations (IHR 2005) on 19 May 2016.
Following the advice of the Emergency Committee, the Director-General concluded that the urban yellow fever outbreaks in Angola and DRC are serious public health events which warrant intensified national action and enhanced international support, but that the situation did not warrant the declaration of a Public Health Emergency of International Concern (PHEIC).
YF is a disease caused by infection with yellow fever virus. It is considered to be one of the most lethal viral diseases. It is transmitted to humans through the bite of infected mosquitoes.
YF occurs in tropical regions of Africa and in parts of South America. It is a very rare cause of illness in travellers to these areas. Endemic regions include countries (or areas within countries) where there is the potential for human infection because of the presence of the mosquito vector and of the YF virus in non-human primates. To date YF has not appeared in Asia or the Pacific region. The WHO estimates that there are approximately 200,000 cases of yellow fever, causing 30,000 deaths, worldwide each year, with 90% occurring in Africa.
The Centers for Disease Control and Prevention (CDC) in the United States maintain a list and maps of countries affected by YF. The WHO maintains a country list of YF vaccination requirements and recommendations.
YF vaccination has two aims:
- To prevent the international spread of the disease by protecting countries from the risk of importing or spreading the yellow fever virus. These are requirements established by the country. And
- To protect individual travellers who may be exposed to yellow fever infection.
WHO notes that the countries that require proof of vaccination are those where the disease may or may not occur and where the mosquito vector and potential non-human primate hosts of YF are present.
Any importation of the virus into such countries by infected travellers could result in its propagation and establishment, leading to a permanent risk of infection for the human population. Proof of vaccination is often required for travellers arriving from countries with risk of YF transmission and sometimes for travellers in transit through such countries (although generally not for very short periods of airport transit (generally <12 hours).
YF vaccine is a safe vaccine which provides long term protection. Immunisation against yellow fever is indicated for the following groups:
- Those travelling to, passing through or living in an endemic area,
- Those travelling to any country that requires an International Certificate of Vaccination or Prophylaxis for entry,
- Those handling potentially infectious materials (e.g. laboratory personnel).
Country requirements for YF vaccination are subject to change at any time. WHO provides ongoing updates on the YF distribution and vaccination requirements.
Information on recent outbreaks of YF can be accessed on the WHO website.
Paul McKeown, HPSC
