Impact of textile durability on the efficacy of three types of dual-active-ingredient long- lasting insecticidal nets: A secondary analysis on malaria prevalence and incidence from a cluster-randomized trial in north-west Tanzania

Abstract

Background The Dual-Active Ingredient long-lasting insecticidal nets (Dual-AI LLIN) have been developed to counteract the reduced efficacy of pyrethroid (PY)-only nets due to widespread pyrethroid insecticide resistance in malaria vector mosquitoes. They constitute half of the nets distributed in sub-Saharan Africa in the past two years. However, their effectiveness once they develop holes is unclear, particularly in pyrethroid-resistant settings. This study evaluates the textile integrity of three dual- AI LLINs compared to standard PY LLN, over 3 years of use in a community in Tanzania and the associated impact on malaria prevalence and incidence. Methods Between 2019 and 2022, we conducted a secondary analysis of data from a randomized controlled trial (RCT) in North-western Tanzania to evaluate the effectiveness of α-cypermethrin only; pyriproxyfen and α-cypermethrin (PPF-PY); chlorfenapyr and α-cypermethrin (chlorfenapyr-PY); and the synergist piperonyl butoxide and permethrin (PBO-PY) LLINs on malaria infection prevalence and case incidence. We assessed the association between the net textile condition and 1/malaria prevalence over 3 years of use, and 2/malaria case incidence in a cohort of children over 2 years of follow-up. Results There was no significant association between damaged (OR: 0.98, 95%CI: 0.71-1.37, p-value=0.6550) and too-torn (OR: 1.07, 95%CI: 0.77-1.47, p-value=0.6940) compared to intact nets on malaria prevalence for all net types. However, there were reduced rates of malaria case incidence in children sleeping under a net in good condition compared to extremely torn nets (incidence rate ratio (IRR) 0·76 [95%CI: 0.63-0.92], p=0.0047). Malaria incidence was also consistently lower in too-torn PBO-PY LLIN (IRR= 0.37 [95%CI: 0.19-0.72], p= 0.0033) and Chlorfenapyr-PY LLIN (IRR= 0.45 [95%CI: 0.33-0.97], p= 0.0525) compared to a intact PY-only LLIN during the first year of follow up. In year 2, the incidence was only significantly lower in intact Chlorfenapyr-PY LLIN (IRR= 0.49 [95%CI: 0.29-0.81], p= 0.0059) compared to intact PY LLIN. Conclusion Our study confirmed that sleeping under a Chlorfenapyr-PY LLIN or PBO-PY LLIN offered superior protection to pyrethroid-only nets even when torn. Care of the net is essential to reduce the development of holes as they impact the level of protection offered against malaria infection. Trial registration ClinicalTrials.gov, number (NCT03554616)