Fig. 3. Spatial distribution and correlates of annual Lassa fever occurrence and incidence (2016 to 2019) at local government authority level across Nigeria.

Maps show fitted probability of LF occurrence (a) and incidence (b; cases per 100,000 persons, visualised on the natural log scale) for 774 LGAs in 2019. Points and error-bars (c) show socio-ecological linear fixed-effects parameter estimates (posterior mean and 95% credible interval) for best-fitting models of Lassa fever occurrence (dark blue; log odds scale) and incidence (pale green, log scale) (n = 3096 observations). Linear covariates were centred and scaled before fitting, so parameters measure the effect of 1 scaled unit change in the covariate (1 standard deviation) on either log odds of occurrence or log incidence. Curves show nonlinear effects of total annual precipitation on LF occurrence (odds ratio; d) and incidence (relative risk; e), specified and fitted as second-order random walks. Models included spatiotemporally structured random effects (LGA per year) to account for geographical heterogeneity and expansion of reporting effort (Methods) and were robust to cross-validation tests (Supplementary Fig. 3) and modelling at lower spatial resolution (Supplementary Fig. 4).