Number of deaths to likely increase 25 per cent; projected to further accelerate in the two regions after 2050
The burden and geography of yellow fever — an acute, viral haemorrhagic disease transmitted by infected mosquitoes — is projected to shift to Central and East Africa from West Africa by 2050, according to a new study.
The number of deaths will likely increase by 25 per cent, with most of them occurring in Central and East Africa, said the July 28, 2020 modelling study by scientists at Imperial College, London and the World Health Organization (WHO). They are projected to further accelerate in the two regions after 2050.
West African countries currently have the largest yellow fever disease burden on the continent. The new findings, however, indicate a shift in this burden to regions outside West Africa.
The Central African Republic is most likely to see an increase in transmission, according to projections estimated by the study. Yellow fever is currently responsible for causing 78,000 deaths in Africa every year.
The climate change affect
The study said climate change-related factors, including temperature and rainfall, would lead to a change in the magnitude and geography of the disease.
Changes in temperature and rainfall in African countries were observed under four scenarios. The force of infection was projected to increase for the majority of countries in each scenario, according to the study.
Deaths could increase around 11 per cent in the best-case scenario and up to 25 per cent in the worst-case scenario by 2050. These figures were projected to be 10 per cent and 40 per cent respectively by 2070.
Yellow fever is endemic in 34 countries in the sub-Saharan African region, despite the existence of a vaccine for the disease. En endemic disease is one where infection is constantly maintained in a geographic area without any external inputs.
There are three transmission ‘cycles’ for the disease in Africa: Urban, zoonotic and intermediate. The study primarily considered the urban transmission cycle in its simulations.
The urban cycle — mediated by Aedes aegypti mosquitoes — is responsible for explosive outbreaks such as the one in Angola in 2016. The urbanisation of African cities and the impact of climate change have put populations at an increasing risk of contracting this infection.
Vaccination is the most important and effective measure against yellow fever, said the study in its recommendations for the Africa. A strategic plan on vaccination to control diseases in the continent must consider the suggestions of the study.
WHO’s Eliminate Yellow Fever Epidemics 2017-2026 strategy, for example, may consider this and focus on Central and East Africa, along with the West Africa region.
West Africa benefited from substantial vaccination campaigns in recent years, but East African countries did not have extensive vaccination, according to the study.
There is, thus, likely to be a greater vaccine demand in these regions which previously had lower risk. Ethiopia and Somalia in East Africa may become higher priority targets for vaccination, the study said.
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