Heterogeneity of use, access, and retention of insecticide-treated nets: Implications for subnational tailoring to maximise malaria control

Background: While insecticide-treated nets (ITNs) are highly impactful and cost-effective for malaria control, they are primarily distributed through three-yearly mass campaigns yet are typically retained for shorter periods. It is unclear whether disease control could be best improved with more efficacious ITNs and/or increased distribution frequency. There are increased calls to optimise resources through subnational tailoring of interventions, though benefits will depend on how long people use ITNs and how this varies between regions; yet this has not been previously quantified subnationally. Methods: We estimated subnational differences in ITN use, access, and retention for six countries (Burkina Faso, Ghana, Malawi, Mali, Mozambique, and Senegal) and used these to calibrate a Plasmodium falciparum transmission dynamics model, generating subnational case estimates under different distribution strategies. Results: On average, people used their ITNs for 21 months though this varied subnationally from 12 to 38 months. Shifting from triennial to biennial campaigns is projected to increase mean use across all regions from 45.4% to 53.9% and avert substantial additional cases in moderate and high transmission settings. Projected case increases following campaign deprioritisation or switching to less efficacious ITN classes are strongly associated with transmission intensity. Conclusions: Although transmission intensity remains important for subnational tailoring, other factors, such as ITN use given access, meaningfully influence optimal deployment strategies. The framework highlights how routinely collected data can aid policymakers in tailoring disease control programmes at subnational levels. Funding: The work was funded by the Global Fund under the Net Transition Initiative. ACG and TSC acknowledge funding from the MRC Centre for Global Infectious Disease Analysis (MR/R015600/1), jointly funded by the MRC and the UK Foreign, Commonwealth and Development Office (FCDO) under the MRC/FCDO Concordat agreement, and part of the EDCTP2 programme supported by the European Union.