Long-lasting residual efficacy of a new indoor residual spraying product, VECTRON™ T500 (broflanilide), against pyrethroid-resistant malaria vectors and its acceptance in a community trial in Burkina Faso
Authors: Hien Aristide Sawdetuo , Bayili Koama , Maiga Samina , Oumbouke Welbeck , Birba Jean , Soma Dieudonné Diloma , Ouattara Adissa Ya , Karama Delphine Ouissamien , Coleman Marlize , Snetselaar Janneke , Small Graham , Niimi Shinya , Ayumi Kawase , Kompaoré Sidzabda , Tsuchiya Katsutoshi , Dabiré Roch Kounbobr , Diabaté Abdoulaye 
Published: November 2024

Abstract
Background
The WHO Global Malaria Programme advocates for a comprehensive, strategic approach to managing insecticide resistance, highlighting the importance of using multiple insecticides with different modes of action through rotations and combinations. To slow the spread of resistance, it is essential to develop and evaluate new formulations that feature unique modes of action and extended residual effects. Addressing this need, Mitsui Chemicals Crop & Life Solutions, Inc., developed VECTRON™ T500, a new indoor residual spraying (IRS) formulation using broflanilide, applied at a dosage of 100 mg AI/m2. This formulation was tested in a Phase III community trial, alongside Actellic® 300CS, a commonly used IRS product containing pirimiphos-methyl, applied at the recommended dosage of 1000 mg AI/m2.

Methods
Monthly WHO wall cone bioassays were performed to assess the efficacy of the interventions using three mosquito strains: the laboratory-bred, insecticide-susceptible Anopheles gambiae s.s. Kisumu strain, the insecticide-resistant Anopheles coluzzii VKPer strain, and wild Anopheles gambiae s.l. mosquitoes from the Vallée du Kou, where the study was conducted. Vector surveillance was carried out to compare the results between sites treated with VECTRON™ T500, Actellic® 300CS, and an untreated control site. In addition, any reported adverse effects were closely monitored to evaluate the community’s acceptance of VECTRON™ T500.

Results
VECTRON™ T500 consistently achieved 100% mortality across all wall types for both susceptible and resistant mosquito strains over the 12-month period. In comparison, Actellic® 300CS induced < 80% mortality for both strains, irrespective of the wall substrate. When assessing delayed mortality in An. gambiae s.l. mosquitoes collected from sites treated with Actellic® 300CS (VK1) and VECTRON™ T500 (VK3), a statistically significant difference was noted after a 72-h holding period compared to the control site (RR = 0.51, CI95% = [0.31–0.6], P = 0.0026). Additionally, no adverse events were reported in households sprayed with VECTRON™ T500.

Conclusions
The residual efficacy of VECTRON™ T500 extended for 12 months post-spraying, effectively covering the full malaria transmission season while maintaining high mortality rates in pyrethroid-resistant malaria vectors. VECTRON™ T500 demonstrated non-inferiority in performance compared to Actellic® 300CS, the standard reference product. This new IRS formulation has the potential to play a crucial role in managing insecticide resistance by being integrated into a rotational strategy alongside other IRS products containing insecticides with different modes of action.

Graphical Abstract