Control of yellow fever (YF) in Africa has been quite successful, with more than 105 million people vaccinated since 2006. Before 2010, most YF outbreaks were reported from 12 West African countries (Benin, Burkina Faso, Cameroon, Côte d’Ivoire, Ghana, Guinea, Liberia, Mali, Nigeria, Senegal, Sierra Leone, and Togo). The introduction of preventive mass vaccination campaigns, together with routine immunization, led to a dramatic decrease in cases. No YF outbreaks occurred in West Africa in all of 2015. Since 2010, however, YF disease activity has shifted to Central and East Africa, regions in which preventive mass vaccination campaigns have not been implemented. Outbreaks have occurred since that year in Chad, the Democratic Republic of Congo, Ethiopia, the Republic of Congo, Sudan, and Uganda — and currently in Angola with spread to Congo.
Four suspected cases of YF in Luanda, Angola, were reported on Dec. 30, 2015, with the index case, a 22-year-old Eritrean, who had symptom onset on Dec. 5. Laboratory confirmation of the case was not accomplished until Jan. 20, 2016, with official declaration of an outbreak two days later. The number of cases increased rapidly such that, as of April 4, a total of 1562 suspected cases and 501 laboratory-confirmed cases, including 225 deaths (case fatality rate: 14.4%), had been reported. The outbreak peaked in February, with the number of confirmed cases now progressively declining.
Participating partners and the Angolan Ministry of Health launched the Incident Management System on Feb. 12 and made a decision to conduct a reactive mass vaccination campaign targeting 6.4 million persons in all the municipalities in Luanda Province. Vector control was implemented. Vaccine was requested from the International Coordinating Group on Vaccine Provision for YF control (YF-ICG) with the first shipment arriving on Feb. 2. However, the vaccination campaigns have met a number of obstacles, including a limited number of vaccination teams, lack of security in some vaccination sites, cold chain problems, shortage of funds, and a limited global supply of YF vaccine. All these factors contributed to delay in completing the planned program. During this delay, YF extended to other provinces of Angola.
This outbreak pointed out an important problem for YF control — a need for vaccine that outstrips the supply. While the planned emergency stockpile for 2016 contained 6 million doses, the reactive mass vaccination campaign conducted in Luanda Province depleted the stockpile, required additional doses, and consumed a total of 7.4 million doses to date. The emergency stockpile has been replenished, but the Angolan Ministry of Health has requested an additional 3.2 million doses.
This outbreak suggests the potential for large-scale urban outbreaks given the rapid urbanization of Africa and the concomitant need for huge numbers of vaccine doses for control. Furthermore, in urban centers such as Luanda that have large international airports, cases (and mosquitoes) may be exported. To interrupt international spread, it is urgent and essential that International Health Regulations be reinforced by requiring travellers to present yellow fever vaccination certificates upon entry to yellow fever endemic countries.
Prevention of YF requires routine vaccination with at least 80% coverage in all at-risk areas. Control of YF outbreaks requires rapid implementation of mass preventive vaccination programs, something that cannot be accomplished if insufficient vaccine is available and if other obstacles are not overcome.