Unravelling the Impact of Insecticide-treated Bed Nets on Childhood Malaria in Malawi

Background: To achieve malaria elimination it is essential to understand the impact of insecticide-treated net (ITNs) programmes. Here, the impact of ITN access and use on malaria prevalence in children in Malawi was investigated using Malaria Indicator Survey (MIS) data. Methods: : MIS data from 2012, 2014 and 2017 were used to investigate the relationship between malaria prevalence in children (6 to 59 months) and ITN use. Generalised linear modelling (GLM), geostatistical mixed regression modelling and non-stationary GLM were undertaken to evaluate trends, spatial patterns and local dynamics, respectively. Results: : Malaria prevalence in Malawi was 27.1 % (95% CI 23.1 -31.2 ) in 2012 and similar in both 2014 (32.1 %, 95%CI 25.5-38.7) and 2017 (23.9 %, 95%CI 20.3-27.4). ITN coverage and use increased during the same time period, with population access growing from 33.1 % (95%CI 29.8-36.4) of the population potentially sleeping under an ITN the previous night to 58.4 % (95%CI 56.2-60.6) and ITN use from 41.1 % (95% CI 37.3-44.9) of the population sleeping under an ITN the previous night to 57.4 % (95% CI 55.0-59.9). The behavioural gap disappeared while the ownership gap persisted. Both the geostatistical and non-stationary GLM regression models showed child malaria prevalence had a negative association with ITN population access and a positive association with ITN use. The non-stationary GLM highlighted the large variation in the relationship between childhood malaria and ITN use across the country. Conclusion: ITNs are effective in controlling childhood malaria in Malawi, although the impact was heterogeneous across the country. This study presents an important modelling approach that allows malaria control programs to spatially disentangle the impact of interventions on malaria cases.