Projecting the future spread of yellow fever vectors and implications for epidemic risk: a scoping review of climate change and human behaviour.

BACKGROUND: Yellow fever is a vector-borne disease with high epidemic potential. Although currently concentrated in Africa and Latin America, both climate change and human behaviour are likely to affect its future spread and epidemic risk. However, how these factors might interact to alter yellow fever distribution remains unclear. OBJECTIVES: This scoping review aimed to map the available literature at the intersection of these topics and compile the trends that may influence the future spread of yellow fever. ELIGIBILITY CRITERIA: Studies were included if they reported original data on future trends in yellow fever epidemiology or vector evolution in the context of climate change, climate variability and human behaviour. Review articles, reports without original data, reports not addressing future trends in yellow fever epidemiology or vector evolution in the context of climatic factors or human behaviour were excluded. SOURCES OF EVIDENCE: Systematic searches of PubMed, Embase and Cochrane CENTRAL were conducted from database inception up to September 2024, alongside manual searches of congress abstract books conducted in September 2024. CHARTING METHODS: The project followed Joanna Briggs Institute methodology for scoping reviews, using Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews guidelines. Searches focused on publications containing data relating to predicting, modelling or forecasting trends over time in yellow fever disease, virus and vector dynamics in relation to climatic factors and/or human behaviour. Search results underwent two-step screening against inclusion and exclusion criteria. Data were manually extracted using a bespoke Excel form, with results classified according to expert opinion. Trends in the dataset were identified using generative artificial intelligence as a drafting aid and all final categorisation and interpretation was determined through expert manual review. RESULTS: In all, 1243 studies were screened and 42 met inclusion criteria. The oldest study was published in 2009, and 67% were published between 2019 and 2024. Most (81%) were modelling studies. Most included studies projected a climate-driven expansion in the range and abundance of major yellow fever vectors, particularly Aedes aegypti, with temperature and precipitation the most frequently examined covariates. Human factors such as urbanisation and population growth were also commonly modelled as amplifiers of exposure risk. Evidence directly linking these projections to future yellow fever transmission was less frequent and more heterogenous. Important knowledge gaps at this topic intersection included limited research on non-Aedes vectors, insufficient information on future yellow fever trends in Africa and limited understanding of how sylvatic cycles might be affected by climate change and human behaviour. CONCLUSIONS: The available literature suggests that changing climatic conditions and human activities such as urbanisation and land use will likely contribute to future increases in yellow fever vector abundance and geographical range. While most relevant analyses suggest that increases in human exposure and transmission risk are likely to follow, evidence related to these factors was more limited.