Comparative Functional Survival and Equivalent Annual Cost of Three Long Lasting Insecticidal Net (LLIN) Products in Tanzania: A Three-Year Prospective Cohort Study of LLIN Attrition, Physical Integrity, and Insecticidal Activity

Background: Almost 1.2 billion long lasting insecticidal nets (LLINs) have been procured for malaria control. World Health Organization (WHO) prequalifies LLINs that remain adequately insecticidal three years after deployment. Institutional buyers often assume that prequalified LLINs are functionally identical with a three-year lifespan. We measured the lifespans of three LLIN products, and calculated their cost per year of functional life, to explore whether using such data for LLIN procurement could lead to more cost-effective product selection. Methods: A randomised double-blinded prospective evaluation of three pyrethroid LLIN products was conducted in 2013 to 2016 among 3,420 study households in Tanzania using WHO-recommended methods. Primary outcome was LLIN functional survival (LLINs present in serviceable condition). Secondary outcomes were 1) bioefficacy and chemical content (residual insecticidal activity) and 2) protective efficacy for volunteers sleeping under the LLINs (bite reduction and mosquitoes killed). Findings: LLIN median functional survival was significantly different: 2·0 years for Olyset, 2·5 years for PermaNet and 2·6 years for NetProtect. Functional survival was affected by accumulation of holes resulting in users discarding nets. Protective efficacy also significantly differed between products as they aged. Equivalent annual cost varied between $1·2 and $1·5 USD, assuming that each net was priced identically at $3. The longer-lived nets were 20% cheaper than the shorter-lived product. Interpretation: LLIN functional survival is less than three years, and differs substantially between products. These differences strongly influence LLIN cost-effectiveness, and cannot be ignored by LLIN buyers who care about value for money. Funding Statement: The research was made possible by the Research Council of Norway through the ABCDR Project no. 220757. Sarah Moore was funded by awards from IVCC and Notre Dame OPP1081737. Declaration of Interests: Sarah Moore, William Kisinza, Olivier Pigeon and Jason Moore conduct product evaluations for a number of vector control product manufacturers. The other authors declare that they have no competing interests. Ethics Approval Statement: Ethical approval was granted from ethical review committees at London School of Hygiene & Tropical Medicine (6333/A443), Ifakara Health Institute (IHI/IRB/AMM/ No: 07- 2014) and the Tanzanian National Institute for Medical Research (NIMR/HQ/R.8c/Vol. I/285).