WHO Phase III Evaluation of Vectron T500 (Broflanilide 50WP) for IRS in Tanzania

Background: Indoor residual spraying (IRS) is one of the major methods of malaria vector control across sub-Saharan Africa, responsible for reducing malaria incidence by 10% since 2000. However, effective vector control is increasingly threatened by the rapid spread of insecticide resistance. Consequently, there have been investments in the development of new insecticides for IRS that possess novel modes of action with long residual activity, low mammalian and environmental toxicity and minimal cross-resistance. VECTRONTM T500, a new IRS insecticide containing the active ingredient broflanilide 50% WP, has been shown to be efficacious against both pyrethroid-susceptible and -resistant vector strains on mud and concrete substrates in phase II experimental hut trials in Tanzania.

Method: A two-arm non-inferiority cluster randomized controlled trial will be conducted in Muheza District, Tanga Region, Tanzania. VECTRONTM T500 will be compared to the IRS formulation Fludora® Fusion (active ingredients: clothianidin 50% WP + deltamethrin 6.25% WP). The predominant malaria vectors in the study area are pyrethroid-resistant Anopheles gambiae s.s., An. arabiensis and An. funestus s.s. Sixteen selected clusters of 75-200 households in each cluster will be pair-matched on baseline vector densities and allocated to reference and intervention arms. Consenting households in the intervention arm will be sprayed with VECTRONTM T500 and those in the reference arm will receive Fludora® Fusion. Monthly CDC light traps will collect mosquitoes to determine vector density, indoor biting, sporozoite and entomological inoculation rates (EIR). Phenotypic resistance to IRS active ingredients will be assessed using CDC bottle bioassays. Molecular and metabolic resistance mechanisms will be characterised among Anopheles field populations from both trial arms. Residual efficacy of both brands of insecticide will be monitored for 12 months post-spraying. A semi-structured questionnaire and focus group discussions will explore social and cultural factors that influence acceptability, perceived adverse effects and benefits of IRS.

Discussion: This protocol describes a phase III non-inferiority evaluation of a novel IRS product to reduce the density and EIR of pyrethroid-resistant Anopheles vectors. If VECTRONTM T500 proves non-inferior to Fludora® Fusion, it may be considered as an additional vector control product for malaria prevention and insecticide resistance management schemes.