Modelling the impact of adopting new-generation insecticide-treated nets on malaria transmission and insecticide resistance

Abstract Background Widespread insecticide resistance increasingly threatens malaria elimination, prompting a reassessment of vector control strategies. As Tanzania transitions from standard pyrethroid-only insecticide-treated nets (ITNs) to new-generation nets, evaluating the impact of this shift on malaria transmission and resistance is critical. Methods Using the agent-based malaria model, EMOD, we assessed the impact of three ITN types, standard pyrethroid-only nets, pyrethroid-PBO nets (Olyset® Plus/PermaNet® 3.0), and the dual-active Interceptor® G2 nets (IG2) on malaria transmission and on modelled changes in resistance genotype frequencies under a simplified multi-locus representation of insecticide resistance. We also evaluated different sequences for introducing the new-generation nets, and the impact of combining ITNs with indoor residual spraying (IRS). The model was calibrated using incidence and prevalence data from two regions in northwestern Tanzania, incorporating transmission seasonality and heterogeneity, insecticide resistance, and behaviours of dominant vectors Anopheles funestus (highly anthropophilic, endophilic) and Anopheles arabiensis (more opportunistic readily biting non-human hosts outdoors). Results Changing from standard pyrethroid-only ITNs to pyrethroid-PBO and thereafter to IG2 ITNs reduced homozygous-resistant An. funestus and An. arabiensis by 71.9% (95% CI 70.8–72.9%) and 81.4% (95% CI 78.7–84.1%), respectively within the vector population, and reduced malaria incidence and prevalence by 63% (95% CI 51.0–74.5%) and 76% (95% CI 66.5–89.2%), respectively, by year nine. Deploying IRS before the peak malaria transmission season in mid-May, in the second year following pyrethroid-PBO ITNs distribution, and repeating this every three years, reduced malaria incidence and prevalence by 68.4% (95% CI 24.4–112.5%) and 73.9% (95% CI 35.4–112.4%), respectively, compared with pyrethroid-PBO ITNs alone. Conclusions In contrast to continuous use of standard pyrethroid-only ITNs, which sustains resistance selection, transitioning to new-generation ITNs, with or without periodic IRS, may disrupt the evolutionary trajectory of pyrethroid resistance, reduce malaria burden, and strengthen progress towards elimination.