African Malaria Control Programs Deliver ITNs and Achieve What the Clinical Trials Predicted

There is robust evidence of the efficacy of insecticide-treated mosquito nets (ITNs) in reducing malaria parasite prevalence, incidence, and all-cause child mortality from carefully conducted trials in subSaharan Africa across a range of transmission settings [1]. Trials have shown ITNs to both significantly reduce Plasmodium falciparum prevalence among children under 5 years old by 13% and postneonatal (1–59 months) all-cause mortality by 18% in areas of stable malaria transmission in Africa [1,2]. However, there have been limited data on the effectiveness of ITNs under routine program conditions at preventing malaria morbidity and child mortality, especially at the national level. This has of course raised serious concerns abou how likely the efficacy of ITNs from trials is translating into real-world effectiveness on the ground. There are certainly examples where a proven effective intervention achieved disappointing results when programs ran into constraints with deployment at wide-scale implementation [3,4]. Stephen Lim and colleagues, in an article published in this week’s PLoS Medicine, should be commended for their rigorous and systematic analysis of national cross-sectional survey datasets in subSaharan Africa assessing the association of ITNs on reducing P. falciparum prevalence in children under 5 and all-cause postneonatal mortality, while controlling for contextual and potential confounding factors [5]. The results show ITN household possession to be associated with a 20% significant reduction in P. falciparum prevalence (from seven surveys in seven countries) and a 23% significant reduction in all-cause child mortality (from 29 surveys in 22 countries). Importantly, these results were consistent across a range of malaria transmission settings and across countries with disparate levels of ITN household coverage. They are also consistent with data from smaller-scale studies that have shown ITNs to be associated with significant reductions in malaria under program conditions [6–10]. The ITN represents a brilliant intervention—it provides individual protection to the person sleeping under it from infected mosquitoes; the insecticide kills mosquitoes that seek a blood meal thereby reducing the overall propensity for transmission in the community [11,12]; and if the person under the net is already infected with the malaria parasite, the ITN prevents them from infecting mosquitoes and leading to more transmission. The ITN is tailored to the biology of the African malaria-carrying Anopheles mosquitoes that prefer to bite humans, bite late at night when people are sleeping (hopefully under an ITN), and rest on vertical surfaces (such as the walls of the ITN) while they digest their blood meal. National ITN mass distribution campaigns have achieved remarkably high household coverage, even among the most poor and rural areas [13–15]. Despite unsubstantiated anecdotes of misuse and non-use [16], given sufficient access to ITNs people use them for protection against malaria [17]. Still, ITNs are not the sole answer to malaria control, and they cost money and need to be continually replaced when they wear out.