Functional survival and equivalent annual cost of long-lasting insecticidal nets against malaria

Two billion long-lasting insecticidal nets (LLINs) have been procured for malaria control. A functional LLIN must be present, in good physical and insecticidal condition, providing protection against disease vectors. The WHO prequalifies LLINs that remain insecticidal for three years, resulting in assumptions that such nets are functionally identical with a 3-year lifespan. We measured the lifespans of three LLIN products and their annual equivalent cost to demonstrate the importance of procuring the most cost-effective LLIN products. A randomized double-blinded trial (2014-2016) assessed three pyrethroid LLIN products (n=10,571) after 10, 22 and 36 months among 3,393 households in Tanzania. Primary outcome was LLIN functional survival. Secondary outcomes were bioefficacy, chemical content and protective efficacy. Median LLIN functional survival was significantly different between the three net products, varying from 2.0 to 2.6 years. Functional survival was affected by accumulation of holes, leading to users discarding nets. Protective efficacy significantly differed between products as they aged. Equivalent annual cost varied between US$1.2-1.5 assuming that each net was priced identically at US$3. The two longer-lived nets were 20% cheaper than the shorter-lived product. These results suggest that LLIN functional survival is less than 3 years and differs substantially between products. These differences strongly influence LLIN value for money. LLIN tendering processes should consider local expectations of cost per year of functional life and not unit price. It is important to monitor the comparative durability new LLIN products entering the market to ensure that the most cost-effective products are procured for malaria control.