In late December of 2015 a patient in the dense urban area of Luanda, Angola presented with symptoms that could have been attributed to any number of tropical vector-borne diseases: a headache, body ache, fever, and nausea. By January their blood test came back positive for yellow fever. They were the first of many.
Over the next six months over 3600 Angolans in all 18 of the country’s provinces would be sickened with this virus. More than 360 of those affected would die, making the outbreak the worst in over four decades for Angola. By May it would start spreading at an alarming rate through both urban and rural areas of neighboring Democratic Republic of Congo (DRC), straining global vaccine supplies and sparking international concerns of a runaway epidemic.
Yellow fever is a virus transmitted through Aedes and Haemogogus mosquitoes. Although most people recover on their own after an initial symptomatic phase of just a few days, a significant number, if untreated, experience a secondary phase of extreme viral toxicity which results in death for roughly 50% of those affected. During this secondary phase patients can become severely jaundiced in the eyes and skin, conferring the distinctive “yellowing” effect and making yellow fever one of the most feared tropical diseases on the planet.
Despite its deadly reputation, yellow fever can be controlled relatively cheaply and effectively with a combination of vector control efforts and vaccination. One dose of yellow fever vaccine confers lifelong immunity. If between 80% and 90% of the population in at-risk areas can be vaccinated the virus ceases to be a significant threat even for the unvaccinated.
During the current outbreak in Angola and DRC vaccination campaigns have had to scale up so quickly, across such large populations and geographies that global vaccine production has struggled to keep up. The World Health Organization (WHO) in July released 19 million doses of yellow fever vaccine to Angola alone from emergency stockpiles. Given that global production is restricted to only four labs and 80 million doses annually, the world’s defenses against yellow fever are stretched thin.
If the disease continues to spread through DRC and other neighboring nations, there may be limited capacity remaining to stop the virus. Furthermore, reports out of DRC indicate complementary shortages of needles and syringes needed to deliver the vaccine, which complicates efforts to scale their vaccination campaigns sufficiently.
As the world’s climate heats up, populations increase and rising numbers of people live in dense urban areas of significant tropical disease risk, it will become more important than ever before to develop effective defenses against emergent epidemics. Much like Zika virus in the Americas, yellow fever in southern and central Africa is posing fundamental questions of our capacity as a global civilization to identify and contain dangerous infectious diseases.