Can dual active ingredient Interceptor G2 insecticide treated net (ITN) replace indoor residual spraying (IRS) efficiently; A case study in Sakassou, Cote d'Ivoire

BackgroundFollowing three rounds of successful Indoor Residual Spraying (IRS) implementation in the district of Sakassou (Cote dIvoire), IRS was withdrawn and replaced by insecticide treated nets (ITNs). This study evaluated the entomological and epidemiological impacts of Interceptor (IG2) ITNs distributed in Sakassou, to determine if the protection offered by IG2 nets was adequate to suppress malaria transmission post IRS withdrawal. MethodsThe Vector Control Optimization Model (VCOM) was adapted to evaluate the effectiveness of the IRS and IG2 deployment on malaria transmission dynamics. Additionally, we used an interrupted time series (ITS) model to analyze routinely reported malaria cases in the district health Information Management System (DHIS2) to determine the epidemiological impact of both interventions. Counterfactual trends were generated for the post IRS withdrawal with IG2. ResultsThe results of the VCOM showed a 55.4% (95%CI, 48.3 - 62.4) reduction in the human biting rate (HBR) when IRS was deployed and 48.8% [95%CI, 42.8 - 54.6]) when IG2 nets were distributed, compared to standard pyrethroid-only nets. No statistical difference was recorded between the HBR of IG2 and IRS (p=0.164). Similarly, there was no statistical difference between the entomological inoculation rate (EIR) of IRS (64.7% [95%CI, 56.6 - 72.8]) reduction and IG2 (61.9% [95%CI, 54.2 - 69.6]) reduction (p=0.616). Furthermore, the ITS showed 26% reduction in malaria cases that was recorded immediately after spraying (IRR = 0.74; 95% CI: 0.62-0.90; p = 0.002) with cumulative impact over time and spray rounds and similarly to IG2 performance (IRR = 1.00; p = 0.200). ConclusionThe study findings suggest that IG2 nets provided comparable entomological efficacy as clothianidin-based IRS but could not adequately suppress malaria cases after IRS withdrawal which could be due to plastic vector feeding behaviour. This study provides evidence that dual AI ITNs such as IG2 may be warranted as a contingency strategy after IRS withdrawal but may require additional studies for full recommendation.