Reductions in malaria cases after deployment of dual-active ingredient insecticide treated nets (ITNs) in Ghana – a Bayesian interrupted time series analysis
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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 climatic conditions, monthly mean values of both modelled vector habitat suitability and temperature suitability for the periods were included. Bayesian Poisson regression time series models were developed to assess the immediate and sustained impact of IG2 ITNs on malaria case trends.
Results
Malaria cases reduced by 30% [odds ratio: 0.70, 95% CrI (0.624, 0.778)] immediately after the distribution of IG2 ITNs in the Western North region. This effect was sustained at six months up to 30 months post-intervention, where cases were reduced by 26% [odds ratio: 0.74, (0.65, 0.75) and 40% [odds ratio: 0.598 (0.495, 0.722)], 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. These findings support the scale-up of these 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.
Key messages
Malaria prevalence and incidence both decreased after deployment of IG2 ITNs in the Western North region of Ghana.
Distribution of IG2 ITNs caused immediate and sustained impact on malaria case reduction.
Dual-active ingredient insecticide-treated nets are effective in field settings and could be deployed at a large-scale.
