Efficacy of Vector Guard®, a mosaic alpha-cypermethrin and piperonyl butoxide- treated net, for the control of pyrethroid resistant malaria vectors; a non- inferiority experimental hut evaluation in Benin

Background: Insecticide-treated nets (ITNs) combining pyrethroids with piperonyl butoxide (PBO) have improved the control of malaria transmitted by pyrethroid-resistant vectors compared to standard pyrethroid-only ITNs. To sustain malaria prevention efforts, a broader range of effective pyrethroid-PBO nets is needed to enhance market diversity and supply resilience. This study evaluated the entomological efficacy and wash durability of Vector Guard®, a new mosaic alpha-cypermethrin-PBO ITN, against pyrethroid-resistant Anopheles gambiae s.l. in southern Benin. Methods An experimental hut trial was conducted in Covè, Benin, against wild, free-flying An. gambiae s.l. Vector Guard® was tested unwashed and after 20 standardized washes, and compared to two WHO-prequalified ITNs: Olyset® Plus (a permethrin-PBO net) and Royal Sentry® 2.0 (an alpha-cypermethrin-only net). Primary outcomes were mosquito mortality and blood-feeding protection. Susceptibility bioassays were conducted to assess local resistance mechanisms. Laboratory cone and tunnel tests were also performed to help explain the finding in the experimental huts. Chemical content analyses was performed to investigate active ingredient wash retention. Vector Guard® was assessed for its non-inferiority to Olyset® Plus following WHO guidance. Results The wild Anopheles gambiae s.l. population at Covè exhibited high frequencies of pyrethroid resistance, with PBO pre-exposure restoring partial susceptibility to alpha-cypermethrin (34% vs. 4% mortality) but not to permethrin (2.0% vs. 2.1% mortality). A total of 6,799 females were collected in the experimental huts. Vector Guard® outperformed both Royal Sentry® 2.0 and Olyset® Plus across all entomological endpoints. Mortality with Vector Guard® was significantly higher than with Olyset® Plus when unwashed (36.4% vs. 17.5%, p < 0.001) and after 20 washes (17.2% vs. 8.7%, p < 0.001). Non-inferiority analysis with pooled data for unwashed and washed nets confirmed that Vector Guard® was non-inferior to Olyset® Plus for both mortality (OR 2.71, 95% CI: 2.26–3.24; NIM: 0.423) and blood-feeding protection (OR 0.53, 95% CI: 0.45–0.62; NIM: 1.359). These findings were supported by cone and tunnel tests. Chemical analysis showed higher wash retention of active ingredients in Vector Guard® (83% for PBO and >94% for alpha-cypermethrin) compared to Olyset® Plus (39.7% for PBO and 69.6% for permethrin). Conclusion Vector Guard® demonstrated superior entomological efficacy and wash durability compared to Royal Sentry® 2.0 and Olyset® Plus, and fulfilled WHO non-inferiority criteria for mosquito mortality and blood-feeding inhibition. These findings supported its addition to the WHO list of prequalified pyrethroid-PBO ITNs and its potential to provide improved malaria control when deployed on a large scale in areas with high levels of pyrethroid resistance.