In a nutshell
- The Problem: Malaria is one of the leading causes of mortality for children under five in the developing world, and also has significant non-mortality-related costs (more here).
- The Program: Distribution of insecticide-treated nets (ITNs), aims to protect individuals from bites by infected mosquitoes, which transmit the disease.
- Track record: ITN distribution has a strong track record of significantly reducing mortality in both repeated, randomized controlled trials and in larger-scale, country-level distribution efforts.
- Cost-effectiveness: Estimates imply very strong cost-effectiveness: $182-$1126 to avert a death (in addition to ~300 less severe malaria episodes).
- Bottom line: ITN distribution is a proven, cost-effective means for preventing child mortality in the developing world.
Previous version of this page:
2009 report on insecticide treated nets
Basics of the program
What is the program? What problem does it target?
Non-severe malaria episodes cause flu-like symptoms, where severe episodes can lead to death. Malaria is one of the leading causes of mortality for children under five in the developing world (more
here). Insecticide-treated nets (including bednets and curtains) can kill and repel mosquitoes, reducing risk of infection.
What are the components required to implement this program - how does it work?
- Nets: There are two types of nets used: insecticide-treated nets (ITNs), which require re-treatment every 6 to 12 months, and long-lasting insecticidal nets (LLINs), which are designed to last for 4-5 years. Untreated nets have little or no effect.
- Delivery mechanism: Large-scale ITN programs use several different methods:
- Private, for-profit markets.
- Not-for-profit, commercial markets combined with social marketing, which sell nets at subsidized prices through existing retail stores.This approach is largely used by Population Services International.
- Highly subsidized or free nets sold or distribued to pregnant women at maternal and child health clinics.
- Nets freely distributed in conjunction with national vaccination campaigns.
- Re-treatment mechanism: Jamison et al. (2006) discusses a program "where householders, community health workers, and program staff worked together to treat the nets."
- Education: The Jamison et al. (2006) also discusses "a campaign to inform the community about the intervention."
Program track record
Micro evidence: Has this program been rigorously evaluated and shown to work?
Effect on overall child mortality: An analysis of high-quality evaluations conducted in sub-Saharan Africa, involving approximately 150,000 total participants, concludes that insecticide treated nets significantly reduced all-cause child mortality (by approximately 18%). This implies that "about 5.5 lives ... can be saved each year for every 1000 children protected with ITNs."
Impact may vary according to the intensity of malaria infection in a specific region.
In addition, the total coverage rate for a community -- the proportion of all people in a given area that use nets -- may affect the impact: higher coverage rates may reduce malaria risk even for those who don't use nets themselves.
Effect on pregnant women: A review of five high-quality evaluations (four conducted in sub-Saharan Africa, one in Asia), involving 6,759 participants, concluded that ITNs reduced malaria among pregnant women and incidences of low birthweight, though their effect on anemia was not statistically significant.
Macro evidence: Has this program played a role in large-scale success stories?
A national program in Kenya is a strong example of a large-scale success of ITN distribution. The Tanzanian and Gambian programs are smaller, but further support the idea that large-scale ITN programs can have the results implied in controlled trials. More on the general idea of "macro evidence"
here.
- Kenya: A national program that introduced millions of insecticide-treated nets, some sold at heavily subsidized prices and some distributed free of charge, began in 2004. The program distributed nets in 45 of Kenya's 70 districts. An evaluation of four districts, selected as representative, found that net ownership (25% to 79%) and the proportion of children sleeping under a net (7% to 67%) rose substantially between 2004 and 2006. A subsequent evaluation of the same four regions in Kenya found significant reductions in mortality.
- Tanzania: An evaluation of a program aiming to reach 480,000 people found a significant reduction in mortality.
- The Gambia: A program that started in 1992 aimed to bring ITNs to all large villages in the country. The review evaluated results in five regions, with a total population of 115,895. The evaluation found a significant reduction in child mortality.
Recommendations and concerns
Do expert reviews of the comparative merits of interventions endorse this one?
See this page for sources consulted.
- Jamison et al. (2006) states, "the need to use existing strategies and interventions [including ITNs] in scaled-up programs more effectively and to deploy them more widely is urgent and merits the highest priority, especially in Africa."
- Copenhagen Consensus and Jamison, Jha, and Bloom (2008) both endorse ITN distribution as part of a combined "Malaria prevention and treatment" intervention. The Copenhagen Consensus ranks this intervention 12th out of all philanthropic opportunities; Jamison, Jha, and Bloom (2008) rates it 3rd among disease-specific opportunities.
What are the potential downsides of the intervention?
The Cochrane review
above discusses the possibility that ITNs may only delay deaths from malaria as opposed to directly preventing them. The authors conclude that "Despite ongoing disagreements on this question among researchers, there is at least one point on which there is consensus: if such a delay in mortality exists it will only occur in very high transmission areas" and "it is important that ITN programmes carried out in areas of high transmission have a well-designed mortality monitoring component alongside implementation."
What versions of the intervention are best?
We do not believe it is safe to extrapolate from
three apparently successful large-scale government distribution programs to the idea that any ITN distribution program is having impact. We do not have enough information to have a clear sense of the specific factors that led to success in these cases. We would guess that ITNs are generally effective when used appropriately and consistently by the people who face high risk of malaria mortality.
Two significant ways in which ITN distributions can vary are discussed below.
ITNs (insecticide-treated nets) vs. LLINs (long lasting insecticidal nets)
Until recently, most nets distributed required retreatment with insecticide every 6-12 months, depending on the insecticide (see
above). Jamison et al. (2006) reports that retreatment of ITNs had caused a logistical and financial challenge for some programs.
Free nets vs. selling nets for a fee
There has been some debate about whether ITNs should be sold or given freely, with some arguing that selling them (even for highly subsidized prices) may improve the likelihood that they get to people who will use them. We believe that the weight of the (limited) available evidence supports giving out ITNs rather than selling them. Evidence implies that charging a fee has significantly reduced demand for the product, without leading to corresponding increases in utilization rates (and has not significantly impacted the costs of the program).
- One high-quality study evaluated the impact of user fees on net purchase and on utilization of the net. A program distributing nets at prenatal clinics in Kenya found that increased prices (from $0 to $0.75, the price at which they were sold) reduced demand by approximately 75%, but was not associated with higher rates of utilization.
- A review of high-quality studies on this general issue cites two other studies. One found that charging for deworming drugs significantly reduced demand while raising little revenue and failing to improve the targeting of recipients; another found that charging for water disinfectant "led to a rapid drop-off in take-up, with no evidence of increased targeting to the most vulnerable" while slightly increasing utilization rates.
- The study on The Gambia (discussed above) reports that individuals given free nets in year one, that were then asked to pay for insecticide to retreat them in year two, resulted in a significant reduction in coverage and a rise in child mortality.
- The study on Kenya's program (discussed above) reports that Kenya began selling nets at substantially high prices starting in 2002. Net coverage rates remained extremely low, at 25%, so in 2004, Kenya sold heavily subsidized nets. In 2006, the program began distributing nets for free, raising net coverage to 79% between 2006 and 2007.
What's the bottleneck to increased coverage?
Jamison et al. (2006) mentions that lack of funds (as well as unspecified logistical challenges) may prevent the achievement of widespread coverage.
Cost-effectiveness
The program in The Gambia, discussed above, cost $92,000 in the first year. (After the first year, it would have cost $150,000 per year to retreat the nets, but the government could not afford it.) The authors of the study estimate that the program averted 1 death for every $600 spent. As this figure is only per death averted, it does not include other possible benefits such as reduced fever episodes and economic burden (more on malaria's effects
here). We estimate that approximately 320 episodes of malaria (most of them mild) are averted for every death averted.
Separately, Jamison et al. (2006) estimates that ITNs cost $5-31 per disability-adjusted life-year (DALY) averted. This implies that ITN distribution is among the most cost-effective programs. (More on the DALY metric
here.)
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Using a simple conversion calculation, we estimate that
$182-$1126 prevents a death from malaria and 320 less severe malaria episodes. Note that cost-effectiveness could vary significantly depending on the extent to which people use ITNs and the overall effectiveness of a given distribution program.
Sources
- AED NetMark. http://www.netmarkafrica.org/ (accessed April 19, 2010). Archived by WebCite® at http://www.webcitation.org/5p6VHHnBM.
- Armstrong Schellenberg, Joanna R. M., et al. 2001. Effect of large-scale social marketing of insecticide-treated nets on child survival in rural Tanzania (PDF). Lancet 357: 1241–1247.
- Cohen, Jessica and Pascaline Dupas. 2007. Free distribution or cost-sharing: Evidence from a randomized malaria prevention experiment (PDF). Global Economy and Development Working Paper 11. Washington, DC: Brookings Institution.
- D'Alessandro, U., et al. 1995. Mortality and morbidity from malaria in Gambian children after introduction of an impregnated bednet programme. Lancet 345: 479-483.
- Fegan, Greg W. et al. 2007. Effect of expanded insecticide-treated bednet coverage on child survival in rural Kenya: A longitudinal study (PDF). Lancet 370: 1035-1039.
- Gamble, C. L., J. P. Ekwaru, and F. O. ter Kuile. 2006. Insecticide-treated nets for preventing malaria in pregnancy. Cochrane Database of Systematic Reviews 2006, Issue 2. Summary available at http://www.cochrane.org/reviews/en/ab003755.html (accessed April 19, 2010). Archived by WebCite® at http://www.webcitation.org/5p6RmENZp.
- Guillet, P., et al. 2001. Long-lasting treated mosquito nets: A breakthrough in malaria prevention (PDF). Bulletin of the World Health Organization 79: 998.
- Jamison, Dean, Prabhat Jha, and David Bloom. 2008. Copenhagen Consensus 2008 challenge paper: Diseases (PDF).
- Jamison, Dean T. et al., eds. 2006. Disease control priorities in developing countries (PDF). 2nd ed. New York: Oxford University Press.
- Kremer, Michael, and Alaka Holla. 2009. Pricing and access: Lessons from randomized evaluations in education and health. In What works in development? Thinking big and thinking small, ed. Jessica Cohen and William Easterly, 91-119. Washington, DC: Brookings Institution Press.
- Lengeler, C. 2004. Insecticide-treated bed nets and curtains for preventing malaria. Cochrane Database of Systematic Reviews 2004, Issue 2. Summary available at http://www.cochrane.org/reviews/en/ab000363.html (accessed April 19, 2010). Archived by WebCite® at http://www.webcitation.org/5p6S58mQu.
- Mathers, Colin D., Majid Ezzati, and Alan D. Lopez. 2007. Measuring the burden of neglected tropical diseases: The global burden of disease framework (PDF). PLoS Neglected Tropical Diseases 1, no. 2.
- Noor, Abdisalan M., et al. 2007. Increasing access and decreasing inequity to insecticide-treated net use among rural Kenyan children (PDF). PLoS Medicine 4, no. 8.