In March 2024 the WHO African Region shared a “disease outbreak news” update on yellow fever (YF) in the region from the beginning of 2023. 13 countries have documented “probable and confirmed cases”, and although the overall risk at regional level has been reassessed as “moderate” and the global risk “remains low”, WHO calls for “active surveillance” due to the potential for onward transmission. The “urban proliferation of Aedes spp. mosquitoes can “significantly amplify transmission risks”, which would lead to “swift outbreaks”. However, thanks to the WHO-led global Eliminate Yellow Fever Epidemics (EYE) secretariat’s coordinated preventative and reactive efforts, vaccination coverage has been “substantially enhanced”. Around 62 million people have been vaccinated in Africa through mass vaccination campaigns.
Yellow fever
WHO describes yellow fever as an “epidemic-prone, vaccine-preventable disease”, which is caused by an arbovirus transmitted mainly through the bites of infected mosquitoes. The incubation period ranges from 3 to 6 days, but many people do not experience symptoms. For those who do, fever, muscle pain, and nausea are common.
A small percentage of cases progress to a “toxic phase” with systemic infection affecting the liver and kidneys. In these cases, patients can have more severe symptoms, such as high-grade fever, abdominal pain and vomiting, and jaundice and dark urine caused by acute liver and kidney failure. Bleeding can occur from the mouth, nose, eyes, or stomach. In half of cases with severe symptoms death can occur within 7 to 10 days.
Yellow fever can be prevented with an effective vaccine, which is described by WHO as “safe and affordable”; a single dose offers sustained immunity and life-long protection, without requiring a booster dose.
Cases in 13 countries
WHO reports that, from the beginning of 2023 until 25th February 2024, a total of 13 countries in the region have documented “probably and confirmed cases” of YF: Burkina Faso, Cameroon, the Central African Republic, Chad, Republic of the Congo, Côte d’Ivoire, the Democratic Republic of the Congo, Guinea, Niger, Nigeria, South Sudan, Togo, and Uganda. Preliminary data for 2023 indicate a case fatality rate (CFR) of 11% and a sex ratio of 1:7 (M: F). The median case age is 25.
“Suboptimal surveillance capacity exists in many affected countries, with data fragmentation, limited integration with routine surveillance and clinical systems, and a lack of standardised case definitions that contribute to underreporting and increased mortality rates.”
WHO’s risk assessment
Within efforts to monitor and respond to infectious disease outbreaks WHO conducted a Rapid Risk Assessment for yellow fever on 12th February 2024. This was intended to reassess the current regional risk of multiple ongoing YF outbreaks and provide recommendations for a more effective and coordinated response.
The regional level risk is described as “moderate” and the global risk “remains low”. However, WHO emphasises the need for “active surveillance” in the context of the potential for onward transmission through viraemic travellers and the presence of the competent vector in neighbouring regions.
For more discussions on infectious disease management, particularly encouraging greater uptake of vaccines for vaccine-preventable diseases, why not join us at the Congress in Washington this April, or subscribe to our newsletters here?
