Yellow fever, an acute vector-borne disease, is estimated to have been responsible for 78,000 deaths in Africa in 2013 according to new research published in PLOS Medicine this week.
The research by Neil Ferguson from Imperial College London, UK and colleagues from Imperial College, WHO and other institutions also estimates that recent mass vaccination campaigns against yellow fever have led to a 27% decrease in the burden of yellow fever across Africa in 2013.
In rural areas next to forests, the virus typically causes sporadic cases or even small-scale outbreaks but, if it is introduced into urban areas, it can cause large explosive epidemics that are hard to control. Although many people who contract yellow fever do not develop any symptoms, some have mild flu-like symptoms, and others develop a high fever with jaundice or hemorrhaging from the mouth, nose, eyes, or stomach. About 50% of patients who develop these severe symptoms die.
Fortunately, an effective vaccine against the disease exists.
While eradication of Yellow fever is not feasible due to the wildlife reservoir, large scale vaccination activities in Africa during the 1940s to 1960s reduced yellow fever incidence for several decades. However, after a period of low vaccination coverage, yellow fever has resurged in the continent. Since 2006 there has been substantial funding for large preventive mass vaccination campaigns in the most affected countries in Africa to curb the rising burden of disease and control future outbreaks.
The authors of the study used sophisticated statistical methods to estimate the burden of yellow fever in Africa based on outbreak data, serological surveys and environmental data but note that there is substantial uncertainty in their estimates because of the difficulty of diagnosing yellow fever and a lack of available data. Therefore the estimates for the number of severe cases of yellow fever in Africa in 2013 range from 51,000 to 380,000, and from 19,000 to 180,000 for deaths due to the disease.
Nevertheless, the study provides the most reliable contemporary estimates for the burden of yellow fever and the impact of vaccination campaigns in Africa. The researchers estimate that vaccination has reduced yellow fever cases and deaths by 27% across Africa, with much higher reductions in some countries targeted by vaccination campaigns.
The authors note that the achievements of the current mass vaccination campaigns could be sustained if a high level of immunization is achieved through a strong EPI [infant immunization] program and preventive vaccination of populations that remain at risk, such as migrants or populations from as yet unvaccinated districts.
Read the study at PLOS Medicine: Yellow Fever in Africa: Estimating the Burden of Disease and Impact of Mass Vaccination from Outbreak and Serological Data.
Image: This photomicrograph shows multiple virions of the yellow fever virus at a magnification of 234,000x. Credit: CDC/Erskine Palmer, modified.