Quantifying the direct and indirect protection provided by insecticide treated bed nets against malaria

Abstract

AbstractLong lasting insecticide treated mosquito nets (LLINs) provide both direct and indirect protection against bites from mosquitoes potentially transmitting malaria. Direct personal protection is provided to net users given both the net’s physical barrier and its insecticidal action. Indirect mass protection for the community is afforded through reduced infectious bites per person annually (entomological inoculation rate, EIR). Quantifying these protective effects can help strategize options for net interventions, particularly as insecticide-resistant mosquitoes spread.These types of protection are inherently linked, rendering it impossible to empirically quantify the contribution of each to the overall ‘community effect’, instead we investigate this with a modelling framework and compare model predictions to trends with Demographic Health Survey (DHS) data.Our modelling exercise predicts that in a situation with an EIR of 100, the reduction in EIR from an untreated net used by 80% of the population is 52% [95% CI: 12% - 84%] for users and 21% [95% CI: 0% - 57%] for non-users. Due to the impact of the insecticide, the reduction in EIR for LLINs is 89% [95% CI: 67% - 98%] for users and 74% [95% CI: 48% - 92%] for non-users, but this protection reduces as insecticide resistance in mosquitoes increases. Modelled trends in the difference in protection between users and non-users across endemicity and net usage levels are consistent with DHS data (2000-2018).This study supports the concept of a community effect from LLINs, highlights the value of blocking and killing mosquitoes for community protection. Achieving high LLIN usage is always preferential, but there remains protection to non-users as the number of people using nets increases.