Malaria control needs mass distribution of insecticidal bednets.

Long-lasting insecticidal bednets (LLINs) are one of the major ways to control malaria, and they are widely accepted worldwide by communities in areas affected by malaria. One LLIN costs about US$5 to manufacture and is effective for about 5 years. They have two kinds of protective effects—one for the people directly under the nets, and one for the community at large. The second effect is important, but often ignored. By achieving high community coverage to ensure a substantial community protection, malaria-control efforts can be more powerful than when only individual protection is attempted. The direct effect of LLINs is to protect the people sleeping under them, and it operates in three ways. First, the insecticide kills some of the Anopheles mosquitoes after a few minutes. Second, the LLIN repels a proportion of the mosquitoes after contact. Third, the net acts as a mechanical barrier to biting. The mechanical barrier provides half or less of the protection, which is why bednets without insecticide are less effective than treated ones. A torn and untreated net offers little or no protection, but a torn pyrethroid-treated net still works well. LLINs provide good protection at only about $1 per net per year, with an average of around 1·7 people using every net. The result is remarkable low-cost protection against disability and death, notably for people who are most vulnerable, including infants, small children, and pregnant women. Insecticidal nets provide good, but not perfect, protection for users, but the community effect can extend the protection beyond that for the individuals under the nets. By greatly reducing malaria transmission, LLINs decrease the risk of others in the community coming into contact with an infected mosquito. Every LLIN user thereby contributes not only to his or her safety, but also to the safety of others—the mass effect. The effect is analogous to herd immunity from vaccines. To have maximum effect within communities, LLIN coverage should be as high as possible, with a target of complete coverage. The mass effect works in three ways. First, mass coverage by LLINs reduces the number of mosquitoes in the community. Second, mass coverage shortens the lifespan of the mosquitoes, thus reducing the possibility for maturation of Plasmodium sporozoites and hence decreasing the proportion of mosquitoes that become infective. Therefore the possibility of transmitting the illness to others is greatly reduced. Third, with some Anopheles species, mass coverage might divert mosquitoes from human to animal biting, thereby reducing humanto-human transmission. However, A gambiae is so anthropophilic that, even with nearly 100% coverage with insecticidal nets, about 80% of blood meals were found to come from human beings. Taken together these effects on the vector population can greatly reduce transmission of disease, but only if the coverage of mosquito nets is sufficiently high. Importantly, at low coverage, the mosquitoes that are deflected by the nets will tend to seek out another human being to bite. There would be little or no reduction in overall transmission, but only a diversion. If transmission was diverted from high-risk to low-risk individuals, that would be beneficial but there would be no major effect on intensity of transmission of malaria in the community. Optimum community protection is achieved when mass coverage with LLINs is combined with universal access for the community to timely and effective treatment in the event of infection. Timely treatment can also be expected to have a community benefit. By clearing the infection in the patient as soon as possible, the individual is not only cured of the disease but is also no longer a reservoir of parasites for transmission to others. Therefore LLINs and timely treatment with appropriate medicines (eg, artemisinin-based combinations) should be seen as a package for protection of the individual and reduction of transmission in the community. In devising bednet policies, many donor agencies aim to protect only the vulnerable groups rather than the entire community, and as a result do not achieve the full Published Online June 21, 2007 DOI:10.1016/S01406736(07)60951-9