Monitoring of Fabric Integrity and Attrition Rate of Dual-Active Ingredient Long-Lasting Insecticidal Nets in Tanzania: A Prospective Cohort Study Nested in a Cluster Randomized Controlled Trial

Simple Summary This study evaluated the physical durability of new types of bed nets with two insecticides incorporated into the fibers (Interceptor G2, Royal Guard, and Olyset Plus) compared to standard nets (Interceptor), which contain a single insecticide (pyrethroid only). These bed nets were distributed in the Misungwi district, Tanzania, in February 2019 and followed up at 6-month intervals up to 36 months post-distribution. During cross-sectional surveys, householders were asked to use the net until the next survey. These nets were supposed to protect the user for three years, but this was not the case in this study. All net types had a life span of much less than three years including the pyrethroid-only net. In response to the questionnaire, most respondents reported that they discarded their nets due to wear and tear and this was evident from the holes accrued in earlier surveys; this effect was more severe with Olyset Plus nets than with standard Interceptor nets and other dual insecticide nets.Abstract Pyrethroid-treated long-lasting insecticidal nets (LLINs) have been the main contributor to the reduction in malaria in the past two decades in sub-Saharan Africa. The development of pyrethroid insecticide resistance threatens the future of LLINs, especially when nets become holed and pyrethroid decays. In this study, three new classes of dual-active ingredient (AI) LLINs were evaluated for their physical durability: (1) Royal Guard, combining pyriproxyfen, which disrupts female fertility, and a pyrethroid, alpha-cypermethrin; (2) Interceptor G2, which combines the pyrrole chlorfenapyr and a pyrethroid (alpha-cypermethrin); (3) Olyset Plus, which incorporates the pyrethroid permethrin and the synergist piperonyl butoxide, to enhance the pyrethroid potency; and Interceptor, a reference net that contains alpha-cypermethrin as the sole active ingredient. About 40,000 nets of each type were distributed in February 2019 to different villages in Misungwi. A total of 3072 LLINs were followed up every 6-12 months up to 36 months to assess survivorship and fabric integrity. The median functional survival was less than three years with Interceptor, Interceptor G2, and Royal Guard showing 1.9 years each and Olyset Plus showing 0.9 years. After 36 months, 90% of Olyset Plus and Royal Guard and 87% of Interceptor G2 were no longer in use (discarded) due to wear and tear, compared to 79% for Interceptor. All dual-AI LLINs exhibited poor textile durability, with Olyset Plus being the worst.