Reductions in malaria cases after deployment of dual-active ingredient insecticide-treated nets in Ghana—a Bayesian interrupted time series analysis

Background: Insecticide-treated nets (ITNs) represent a key tool in reducing human vector contact for malaria control. However, increasing insecticide resistance of malaria vectors threatens the effectiveness of pyrethroid-only nets in reducing malaria risk. Next-generation nets, such as those with dual-active ingredients, have been recommended for use in areas with high malaria burden and confirmed pyrethroid resistance. Here, we assessed the impact of the distribution of Interceptor^® G2 (IG2) ITNs on malaria cases in the Western North Region of Ghana distributed in 2021. 

Methods: We analysed monthly numbers of confirmed malaria cases reported by health facilities in the Western North Region from 2018 to 2023. To control for possible confounding effects of climate, monthly mean values of modelled vector habitat suitability and temperature suitability were included. Bayesian Poisson regression time series models were developed to assess the immediate and sustained impact of IG2 ITNs on malaria case trends measured as odds ratio (OR) with their corresponding credible intervals (CrI). 

Results: Malaria cases reduced by 30% (OR, 0.696; CrI, 0.623–0.778) immediately after the distribution of IG2 ITNs in the Western North Region. This effect was sustained at 6 months up to 30 months post-intervention, where cases reduced by 26% (OR, 0.739; CrI, 0.653–0.837) and 40% (OR, 0.594; CrI, 0.492–0.718), respectively. The intervention was also strongly associated with reductions in malaria cases in seven of the nine districts in the region, after controlling for climatic factors. 

Conclusion: This study demonstrates the effectiveness of dual-active Interceptor^® G2 ITNs in the Western North Region, an area with confirmed pyrethroid resistance. The findings support the scale-up of next-generation nets by National Malaria Programs and highlight the need for further research to explore the utility of these nets in other high-burden malaria areas with region-specific insecticide resistance profiles.