Efficacy of SumiShield 50WG assessed for non-inferiority in comparison with Actellic 300CS applied by indoor residual spraying (IRS) against resistant Anopheles arabiensis mosquitoes in Tanzania: results from an experimental hut trial and a community randomised entomological trial

Background New insecticides for use against resistant Anopheles mosquitoes are needed for continued global progress in malaria control. SumiShield 50WG (clothianidin), a neonicotinoid insecticide for indoor residual spraying (IRS), was assessed for non-inferiority in comparison with Actellic 300CS (pirimiphos-methyl), the standard IRS, against pyrethroid-resistant and pirimiphos-methyl-susceptible Anopheles mosquitoes. Methods The efficacy of SumiShield 50WG for IRS against Anopheles arabiensis mosquitoes was compared to Actellic 300CS over 8 months in: (1) an experimental hut trial (EHT) to evaluate mosquito mortality and (2) in a cluster randomised controlled trial (cRCT) that evaluated sporozoite infection in communities in Ulanga, south-eastern Tanzania between 2016 and 2017. Results In the EHT, there were 270 hut-nights per arm. The estimated odds ratio (OR) for mortality for Sumishield 50WG compared to Actellic 300CS after holding exposed mosquitoes for 72 h was 1.22 (95% CI 1.05, 1.43), and for 168 h was 1.19 (1.02, 1.38). Since the lower bounds of the confidence intervals were higher than the margin of non-inferiority (equivalent to a 7% lower mortality following WHO guidelines), then there was evidence of non-inferiority. SumiShield 50WG was also associated with increased mortality. SumiShield 50WG was not shown to be non-inferior compared to Actellic 300CS for the proportion of mosquitoes infected in the cRCT (OR: 1.45, 95% CI 0.59, 3.59), but there were very low numbers of sporozoite-positive mosquitoes, overall leading to substantial uncertainty in the estimates. Conclusions SumiShield 50WG was non-inferior to Actellic 300CS at killing mosquitoes in an experimental hut trial in this setting, and may be useful as an additional tool for insecticide resistance management. Assessing the comparative efficacy of IRS products on sporozoite infection in mosquitoes can be challenging as IRS products reduce the density of mosquitoes. Methods to increase the power by increasing the number of clusters and mosquito sampling would be needed for future cRCT in the trial area.