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This is an archived version of this page. For more up-to-date information, see our most recent report on LLINs.
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.1
Effect on overall child mortality: An analysis of high-quality evaluations conducted in sub-Saharan Africa,11 involving approximately 150,000 total participants,12 concludes that insecticide treated nets significantly reduced all-cause child mortality (by approximately 18%).13 This implies that "about 5.5 lives ... can be saved each year for every 1000 children protected with ITNs."14
Impact may vary according to the intensity of malaria infection in a specific region.15
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.16
Effect on pregnant women: A review of five high-quality evaluations (four conducted in sub-Saharan Africa, one in Asia), involving 6,759 participants,17 concluded that ITNs reduced malaria among pregnant women and incidences of low birthweight, though their effect on anemia was not statistically significant.18
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.
See this page for sources consulted.
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."31
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.32
Two significant ways in which ITN distributions can vary are discussed below.
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.33
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).
Jamison et al. (2006) mentions that lack of funds (as well as unspecified logistical challenges) may prevent the achievement of widespread coverage.44
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.)45 The authors of the study estimate that the program averted 1 death for every $600 spent.46 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.47
Separately, Jamison et al. (2006) estimates that ITNs cost $5-31 per disability-adjusted life-year (DALY) averted.48 This implies that ITN distribution is among the most cost-effective programs.49 (More on the DALY metric here.)
Note: In September 2011, we confirmed a number of errors in the estimates for the cost-effectiveness of deworming published in the Disease Control Priorities report. Based on those findings, we are currently rethinking our use of cost-effectiveness estimates, like the DCP2's, for which the full details of the calculations are not public. For more information, see our blog post on the topic.
Using a simple conversion calculation,50 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.
"The use of ITNs (bednets, curtains, and other materials) to provide personal protection by killing or repelling mosquitoes is one of the major strategies of malaria control (RBM 2002)." Jamison et al. 2006, Pg 421.
"In relation to insecticide, we considered permethrin and deltamethrin. Deltamethrin is effective for a year; thus, re-treatment is annual. Permethrin lasts for six months; thus, we assumed two treatments per year if the transmission season is longer than six months." Jamison et al. 2006, Pg 423.
Guillet et al. 2001, Pg 998.
"There was a small non-statistically significant difference in the summary results of protective efficacy in the two comparisons âˆ’ controls with no nets versus controls with untreated nets: 17% versus 23% reduction in mortality. The summary rate differences in the two comparison groups were virtually identical (5.5 versus 5.6 averted deaths per 1000 per year)." Lengeler 2004, Pg 8.
Noor et al. 2007, Pg 1342. For more on the NetMark initiative, see AED NetMark.
Noor et al. 2007, Pg 1342.
Noor et al. 2007, Pg 1342.
"During the first phase, 21 of Kenya's 70 districts were selected for distribution of LLINs from 8 to 12 July 2006 and integrated with the national measles catch-up vaccination campaign. Health facilities and centralised non-health facility posts were identified by the Kenya Expanded Programme on Immunisation and used as delivery points of both measles vaccine and LLINs to each child under the age of 5 y." Noor 2007, Pg 1342.
Jamison et al. 2006, Pg 423. The quote continues, "In relation to insecticide,we considered permethrin and deltamethrin. Deltamethrin is effective for a year; thus, re-treatment is annual. Permethrin lasts for six months; thus, we assumed two treatments per year if the transmission season is longer than six months."
Jamison et al. 2006, Pg 423.
"Five cluster randomized controlled trials examined child mortality from all causes (Appendix 3). They were all conducted in areas with stable malaria in sub-Saharan Africa: (Burkina Faso (Habluetzel); Gambia (D'Alessandro); Ghana (Binka); Kenya (Nevill); Kenya (Phillips-Howard)). Four of the trials did not use any nets as the control group, and one trial used untreated nets. Both the relative and the absolute impact were analysed." Lengeler 2004, Pg 8.
Lengeler 2004, Pg 43.
"Five cluster randomized controlled trials examined child mortality from all causes... When the ï¬ve trials were pooled regardless of the type of control group, the summary relative rate was 0.82 (95% CI: 0.76 to 0.89; Analysis 1.1), giving a summary protective efï¬cacy of 18%." Lengeler 2004, Pg 8.
"ITNs provided 17% protective efficacy (PE) compared to no nets (relative rate 0.83, 95% confidence interval (CI) 0.76 to 0.90), and 23% PE compared to untreated nets (relative rate 0.77, 95% CI 0.63 to 0.95). About 5.5 lives (95% CI 3.39 to 7.67) can be saved each year for every 1000 children protected with ITNs. In areas with stable malaria, ITNs reduced the incidence of uncomplicated malarial episodes in areas of stable malaria by 50% compared to no nets, and 39% compared to untreated nets; and in areas of unstable malaria: by 62% for compared to no nets and 43% compared to untreated nets for Plasmodium falciparum episodes, and by 52% compared to no nets and 11% compared to untreated nets for P. vivax episodes." Lengeler 2004, Pgs 1-2.
"A related aspect of programme monitoring is the question of how impact varies with the coverage rate. Especially under high transmission conditions, maximum impact might well be obtained only if a certain level of coverage is achieved and if a substantial part of the mosquito population is killed as a result. Such a “mass effect” has been detected in some trials and not in others, but it is likely that if it is present the impact of ITNs will be enhanced (Lines 1992). Recently, a series of studies have clearly documented a “mass effect” on malaria morbidity (Howard 2000) and especially on child mortality (Binka 1998; Hawley 2003). In Ghana and western Kenya, children living in control areas but within a few hundred meters of an intervention cluster experienced the same reductions in mortality as children in the intervention areas. Since such a “mass effect” is very likely to occur before 100% coverage is achieved, this has potentially important consequences for equity: poorer segments of the population unable to afford an ITN might well benefit from the ITNs used by their better-off neighbours." Lengeler 2004, Pg 11.
"The trials included a total of 6759 pregnant women." Gamble, Ekwaru, and ter Kuile 2006, Pg 6.
"Six randomized controlled trials were identified, five of which met the inclusion criteria: four trials from sub-Saharan Africa compared ITNs with no nets, and one trial from Asia compared ITNs with untreated nets. Two trials randomized individual women and three trials randomized communities. In Africa, ITNs, compared with no nets, reduced placental malaria in all pregnancies (risk ratio (RR) 0.79, 95% confidence interval (CI) 0.63 to 0.98). They also reduced low birthweight (RR 0.77, 95% CI 0.61 to 0.98) and fetal loss in the first to fourth pregnancy (RR 0.67, 95% CI 0.47 to 0.97), but not in women with more than four previous pregnancies. For anaemia and clinical malaria, results tended to favour ITNs, but the effects were not significant. In Thailand, one trial randomizing individuals to ITNs or untreated nets showed a significant reduction in anemia and fetal loss in all pregnancies but not for clinical malaria or low birthweight." Gamble, Ekwaru, and ter Kuile 2006, Pg 1.
"In June 2004, DFID approved an additional US$19 million to PSI to establish a parallel distribution system of heavily subsidised ITNs to children and pregnant women through Maternal and Child Health (MCH) clinics, recognizing that these vulnerable groups might not be able to access socially marketed commercial sector nets. The programme began in October 2004, and during the first 6 months Supanet ITNs were bundled with separate Powertab net treatment tablets (for every 6 mo) and distributed to MCH attendees. In May 2005 an additional US$37 million was committed by DFID to PSI to procure and distribute Supanet-branded long-lasting insecticidal nets (LLINs), Olyset and Permanet. These public sector nets were heavily subsidized pretreated nets (KES50; US$0.7) and branded with the MoH logo ...
In April 2004, Kenya's application was successful and US$17 million was approved to procure and distribute 3.4 million LLINs (Olyset and Permanet brands) free of charge to children under the age of 5 y. This represented, at the time, the largest successful award for free distribution of LLINs in Africa. The implementation of the free mass distribution of LLINs was arranged in two phases during 2006. During the first phase, 21 of Kenya's 70 districts were selected for distribution of LLINs from 8 to 12 July 2006 and integrated with the national measles catch-up vaccination campaign. Health facilities and centralised non-health facility posts were identified by the Kenya Expanded Programme on Immunisation and used as delivery points of both measles vaccine and LLINs to each child under the age of 5 y. A second mass distribution of LLINs, not integrated with any other intervention, took place from 25 to 27 September 2006 in 24 additional districts using previous mass vaccine campaign delivery centres as distribution points." Noor et al. 2007, Pg 1342.
"The study was carried out in four districts purposively sampled in collaboration with the MoH to provide detailed longitudinal milestone data on changing access to interventions proposed within the Kenya National Malaria Strategy between 2001 and 2006 [21,22]. The study districts represent the range of dominant malaria epidemiological situations that prevail across Kenya: Kwale on the coast with seasonal high-intensity malaria transmission; Bondo on the shores of Lake Victoria with perennial high-intensity transmission; Greater Kisii district (combining the new districts of Kisii Central and Gucha) with seasonal low transmission conditions of the Western highlands; and Makueni district, a semiarid area with acutely seasonal low malaria transmission. Between 63% and 71% of households in the rural areas of each of the four districts were living below the poverty line (equivalent to US$1 per day) in 1999, compared to the national average of 54% . The districts were also representative of rural districts in Kenya with respect to net delivery since 2001." Noor et al. 2007, Pgs 1342-1343.
Noor et al. 2007, Pg 1344, Table 1.
"The establishment of prospective surveillance in a sample of rural communities in four sentinel districts (Bondo, Kwale, Makueni, and Kisii) has been described in detail elsewhere." Fegan et al. 2007, Pg 1035.
"ITN use was associated with a 44% reduction in mortality (mortality rate ratio 0Â·56, 95% CI 0Â·33–0Â·96; p=0Â·04). This level of protection corresponds to about seven deaths averted for every 1000 ITNs distributed." Fegan et al. 2007, Pg 1035.
"Socially marketed insecticide-treated nets were introduced step-wise over a 2-year period from May 1997, in a population of 480,000 people. Cross-sectional coverage surveys were done at baseline and after 1, 2, and 3 years. A demographic surveillance system (DSS) was set up in an area of 60 000 people to record population, births, and deaths. Within the DSS area, the effect of insecticide-treated nets on child survival was assessed by a case-control approach. Cases were deaths in children aged between 1 month and 4 years.... Insecticide-treated nets were associated with a 27% increase in survival in children aged 1 month to 4 years (95% CI 3–45)." Armstrong Schellenberg et al. 2001, Pg 1241.
"The Gambia initiated a National Insecticide Impregnated Bednet Programme (NIBP) in 1992 with the objective of introducing this form of malaria control into all large villages in The Gambia." D'Alessandro et al. 1995, Pg 479.
"Five areas (population 115,895) were chosen as sentinel sites for evaluation of the NIBP." D'Alessandro 1995, Pg 479.
"The treatment of nets was associated with a reduction in all-cause mortality in all age groups in all areas, with the exception of children aged 1-2 years in area 5 (table 2). Overall, a 25% reduction in mortality in children aged 1-9 years (p=0-04) was seen in treated villages (table 3)." D'Alessandro 1995, Pg 481.
Jamison et al. 2006, Pg 428.
Copenhagen Consensus Center, "Copenhagen Consensus 2008."
Jamison, Jha, and Bloom 2008, Pg 51. Nets are included in the program: "Prevent transmission of and mortality from malaria by expanding coverage of insecticide-treated bednets, by expanding use of intermittent preventive treatment for pregnant women; and by use of indoor residual spraying with DDT." Jamison, Jha, and Bloom 2008, Pg 32.
"Different researchers have hypothesized that where malaria transmission is particularly high, the benefits of ITNs will be transitory, and that morbidity and mortality may only be postponed to an older age as a result of preventing the natural development of immunity to malaria that occurs through repeated exposure (Lines 1992; Snow 1994; Snow 1995; Snow 1997; Trape 1996). This does have obvious serious implications for decision-making, and this view has been discussed and sometimes challenged by a number of other authors (D'Alessandro 1997a; Greenwood 1997; Lengeler 1995; Lengeler 1997b; Lines 1997; Molineaux 1997; Shiff 1997; Smith 2001). 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 (a commonly quoted cut-off entomological inoculation rate is 100, although this is at present based on little evidence).
Unfortunately, there is little evidence for or against such a delayed mortality effect following interventions that potentially interfere with the development of natural immunity... Certainly, stopping or delaying ITN programme implementation because of this fear is not warranted and should even be considered unethical in the light of good evidence of benefit. However, it is important that ITN programmes carried out in areas of high transmission have a well-designed mortality monitoring component alongside implementation." Lengeler 2004, Pg 11.
These are pregnant women and children under five, as stated at our discussion of malaria.
"Re-treating ITNs semiannually or just before the annual peak in transmission is essential for effective vector control and is proving a major logistical and financial challenge. Fortunately, new types of nets with a long-lasting insecticidal property are now available, and retreatment will soon cease to be an issue." Jamison et al. 2006, Pg 421.
"This is very consistent with the results based on net sales; they suggest that demand for ITNs is 75 percent lower at the current cost-sharing price in Kenya (50Ksh or $0.75) than it would be under a free distribution scheme." Cohen and Dupas 2007, Pg 11. See also Figure 1, Pg 11.
Cohen and Dupas 2007, Pg 15, Figure 2.
"When a school-based NGO deworming program in western Kenya introduced cost sharing, the take-up of deworming medication fell sharply and revenue failed to outpace administrative costs, despite the health and education benefits of the program. User fees did not help target treatment to the sickest children. As deworming pills are delivered directly into children's mouths, there was no gap between take-up and usage, so pricing had no potential psychological impact on use through sunk costs." Kremer and Holla 2009, Pg 95.
"Two-stage pricing randomization has also been used to test the two potential routes by which pricing could affect use in a door-to-door marketing campaign for water disinfectant on the outskirts of Lusaka, Zambia. As with deworming and nets, pricing led to a rapid drop-off in take-up, with no evidence of increased targeting to the most vulnerable. Pricing had no statistically significant psychological effect on use. The authors of the study argue that there was some screening effect since those who were more willing to pay for the disinfectant were more likely to have chlorine in their water at later random checks than those who received it for free." Kremer and Holla 2009, Pg 99.
"In 1993 a cost-recovery programme was introduced and villages given free insecticide during the first year of the study were asked to pay 5.00 Dalasi (US$0.50) per bednet treated. Unfortunately this led to a dramatic drop in coverage and a return of child mortality rates in these villages to their pre-intervention values." D'Alessandro et al. 1995, Pg 483.
"In January 2002 the UK Department for International Development (DFID) awarded PSI-Kenya US$33 million over 5 y to socially market partially subsidised ITN within the existing retail sector... A two-tier pricing system of 350 Kenya Shillings (KES) (equivalent to US$4.7) in urban settings versus KES100 (US$1.3) in rural settings was implemented." Noor et al. 2007, Pg 1342.
Noor et al. 2007, Pg 1344, Table 1.
"The programme began in October 2004, and during the first 6 mo Supanet ITNs were bundled with separate Powertab net treatment tablets (for every 6 mo) and distributed to MCH attendees. In May 2005 an additional US$37 million was committed by DFID to PSI to procure and distribute Supanet-branded long-lasting insecticidal nets (LLINs), Olyset and Permanet. These public sector nets were heavily subsidized pretreated nets (KES50; US$0.7) and branded with the MoH logo ." Noor et al. 2007, Pg 1342.
"During round four of the GFATM awards in April 2004, Kenya's application was successful and US$17 million was approved to procure and distribute 3.4 million LLINs (Olyset and Permanet brands) free of charge to children under the age of 5 y. This represented, at the time, the largest successful award for free distribution of LLINs in Africa." Noor et al. 2007, Pg 1342.
Noor et al. 2007, Pg 1344, Table 1.
"Goodman, Coleman, and Mills (2000) find that even though some interventions are relatively cheap, achieving high coverage may require a level of expenditure currently out of reach for many African countries and that overcoming operational barriers to achieving widespread coverage is likely to require substantial assistance from external donors." Jamison et al. 2006, Pg 422.
D'Alessandro et al. 1995, Pg 483.
"The 1992 NIBP campaign cost about US$92 000, 60% of which was attributed to the cost of insecticide. Annual cost of insecticide needed to treat all bednets in The Gambia would be about US$150 000, a sum beyond the means of the Gambian Ministry of Health.villages to their pre-intervention values. In 1992, the estimated cost of death averted was about US$600, a sum that compares favourably with other successful health interventions such as measles vaccination and oral rehydration solutions (in preparation). Therefore, even on a national scale, insecticide treatment of bednets is a cost-effective method of malaria control. Finding new ways of financing such programmes is now a matter of priority." D'Alessandro et al. 1995, Pg 483.
Mathers, Ezzati, and Lopez 2007, Pg 8, Table 3.
Jamison et al. 2006, Pg 424, Table 21.6.
See Jamison et al. 2006, Pgs 41-42, Figures 2.2 and 2.3 for a chart of the cost-effectiveness range (measured in cost per DALY) for many programs.
Mathers, Ezzati, and Lopez (2007, Pg 8, Table 3) implies that each episode of malaria averted counts for 0.1 DALYs, and that 1 in approximately 320 cases (the ratio between deaths and episodes) results in a death and thus an additional 33 DALYs. This in turn implies that $5-31 per DALY is equivalent to $0.57-$3.51 per episode averted, and so ~$182-$1126 would avert the ~321 episodes necessary to avert a single death.