Fig. 4. Enhanced global baseline disease, vector and transmission-risk models for the early 21^st century.

The risk of transmission is estimated as the fuzzy intersection (∩) between favourable conditions for the occurrence of yellow fever cases, and favourable conditions for the presence of vector species. Compared to the models in Fig. 3, additional predictor variables only available for the 21^st century were considered. Recorded occurrences of yellow fever cases and of vector presences are also mapped. The Favourability values were considered on the following scale: High (F > 0.8); high-intermediate (0.5 ≤ F ≤ 0.8); Low-Intermediate (0.2 ≤ F < 0.5); and Low (F < 0.2). The spatial resolution is based on 7774- km² hexagons. Recorded occurrences of yellow fever cases and of vector presences are also mapped (see “Yellow fever datasets” and “Vector dataset” in the Methods section for details). Mosquito and humans clip art source: http://www.freepik.com.