Will a lack of fabric durability be their downfall? 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

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. Preventing the development of holes is essential as they impact the level of protection offered against malaria infection. Trial registration ClinicalTrials.gov, number (NCT03554616)