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Published: December 2012
This page discusses the case for mass distribution of long-lasting insecticide-treated nets (LLINs) for protection against malaria. In general, we focus our discussion on work similar to that of the Against Malaria Foundation.
This intervention involves trying to achieve universal ownership of LLINs within a population, giving free new LLINs to the people who do not already have them. Evidence suggests that when large numbers of people use LLINs to protect themselves while sleeping, the burden of malaria can be reduced, resulting in a reduction in child mortality among other benefits.
LLINs cost under $10 each to purchase and distribute (including all costs), and this intervention is generally considered to be among the most cost-effective ways to save lives. We estimate one life saved for just under $2,300 (this does not include other benefits of ITNs).
Previous versions of this page:
Malaria is one of the leading causes of child deaths in Africa.1 It is transmitted from person to person by infected mosquitoes.2 It involves flu-like symptoms including fever.3 As discussed below, there is evidence connecting malaria with death (particularly in children under 5), anemia, splenomegaly (enlarged spleen), other nutrition-deficiency-related indicators, and low birthweight.
It is also believed that malaria can cause permanent disability (hearing impairment, visual impairment, epilepsy, etc.).4
An insecticide-treated net (ITN) is a net (usually a bed net), designed to block mosquitoes physically, that has been treated with safe, residual insecticide for the purpose of killing and repelling mosquitoes, which carry malaria.5 A long-lasting insecticide-treated net (LLIN)6 is an ITN designed to remain effective for multiple years without retreatment.7 The World Health Organization recommends that LLINs be distributed for free to achieve universal coverage (one LLIN for every two persons) of those at risk for malaria.8 An LLIN distribution involves surveying people to determine the need for LLINs; delivering LLINs; and promoting the use of LLINs (to read our notes from visiting an ongoing LLIN distribution, see our page on October 2011 site visits).
The best evidence for the effectiveness of LLIN distributions comes from randomized controlled trials of insecticide-treated net campaigns, which are reviewed in two Cochrane reviews (Lengeler 2004a; Gamble et al. 2006). We have separately found, examined, and summarized the papers reviewed in Lengeler 2004a.9 The studies are mostly short-term, examining insecticide-treated nets (not necessarily LLINs) over a period of 6 months to 2 years.
Lengeler's (2004a) meta-analysis, examining 22 studies,10 found:
Note that the above figure ("5.53 deaths averted per 1000 children protected per year") is based on people who could be covered by the ITNs distributed, not on people who are confirmed to be using ITNs (i.e., the implication is that .00553 lives are saved for every child under five who could be covered by a distributed ITN, not that .00553 lives are saved for every child under five who is confirmed to be using an ITN).13
Gamble et al. (2006) focused on the effects on pregnant women; it examined fewer studies than Lengeler (2004a) (6 vs. 24). It connected ITNs with statistically significant reductions in the risk of low birthweight and fetal loss (only in women with four or fewer previous pregnancies) and in placental malaria (overall), but not in anemia/haemoglobin measures.21
We focus here on Lengeler (2004a) because (a) it reviewed more studies; (b) it had a general-population focus and was thus more in line with the programs we seek to evaluate and the effects we seek to assess (particularly the effects on mortality).
We have examined and summarized the papers reviewed in Lengeler (2004a),22 seeking to better understand the basic approaches of the programs that led to the results discussed above. We found:
Many studies report intensive measures to ensure that people used their ITNs consistently and properly - measures well beyond what we would expect to be feasible in a larger-scale distribution (and well beyond the measures taken by the Against Malaria Foundation). Sample quotes:23
Usage does not appear to have been near-universal. Most studies report usage rates in the range of 60-80%, though some report 90%+ usage.
The author of Lengeler (2004a) has stated to us that few if any randomized controlled trials have been done since this review, and that few are likely to be done, since the efficacy of ITNs is well enough established that such studies could face challenges with ethics boards.25
Funding for malaria control has increased substantially since 2004, making a large number of national scale-ups possible.26
As noted above, the studies discussed above may have differed substantially from what can be expected of an "average" ITN distribution. The review author notes this, stating, "the bulk of data in this review describe impact under ideal trial conditions (efﬁcacy) rather than impact under large-scale programme conditions (effectiveness). While the difference between efﬁcacy and effectiveness is likely to be small for certain medical interventions (such as vaccination or surgery), it can potentially be large for preventive interventions such as ITNs."27
In order to get a sense for how the large-scale performance of LLINs has compared with the promise of the smaller-scale studies discussed above, we have asked the following key questions:
We feel that malaria scholars have used reasonably credible data to provide helpful answers to #1 and #2. We feel that #3 is substantially harder to answer due to issues with malaria data and the difficulty of isolating the impact of LLINs; it seems likely to us that malaria has generally been on the decline since the increase in LLIN distribution began (and that it was not before the increase began), but we do not have enough information to be highly confident that this is the case, or to confidently attribute the change to LLIN distribution as opposed to other control measures. Details follow.
It appears to us that malaria control programs commonly use an "8%-20%-50%" model to estimate the percentage of distributed LLINs that remain in the field years later: they assume that 8% of LLINs distributed 0-12 months ago are no longer in the field (whether because of loss in the process of delivery, falling into disrepair, being given away, etc.) The very limited evidence we have seen on this topic appears consistent to us with the idea that this model is the best available. Further discussion of this topic is available at another page, for the sake of brevity.
The 2010 World Malaria Report tabulates results from national population surveys and compares (a) the percentage of the population that could theoretically be protected by owned ITNs, based on an assumption that each ITN protects two people;28 (b) the percentage of the population that reports using an ITN.29 It finds 2% ownership/0% use for Swaziland, apparent 100% use for Rwanda, and just over 100% use for Democratic Republic of the Congo and Madagascar (this could be a function of more than 2 people covered by each ITN in some cases, combined with possible over-reporting of usage in surveys). Putting these countries aside, the 8 remaining countries have 40%-85% apparent usage using this model (all but one have 69%+ apparent usage). Using an assumption of 1.8 people covered per ITN, rather than 2 (as we do in our cost-effectiveness analysis below),30 would result in 44-94% estimated usage for these countries (77%+ for 7 of 8). The report displays charts that show strong relationships between the two figures (apparent ITN ownership and apparent ITN use).31
It is possible that survey data overstates usage; in our discussion of small-scale studies above, we cite one study where actual usage (as assessed by spot visits to homes) was 70-73% while reported usage was 85%. Applying this ratio to the reported figures assuming 1.8 people covered per net generates a range (for the seven "mid-range" countries discussed above32) of 63%-81% usage,33 similar to the range reported in small-scaled studies.34 These figures imply usage of ITNs that is, very broadly speaking, as good as what was found in the small-scale studies discussed above, though this data and our analysis of it could easily be unreliable.35
Funding for malaria control has increased substantially since 2004, making a large number of national scale-ups possible. Accordingly, we have looked into the question of whether the impact of LLINs on the burden of malaria can be directly seen in available data (outside the context of intensive small-scale studies). Our discussion is on a separate page, for brevity.
In brief: data and studies appear to show some cases of apparent malaria control success, and also seem to indicate that the overall burden of malaria in Africa is more likely to be falling than rising. However, in most cases it is difficult to link changes in the burden of malaria to particular malaria control measures, or to malaria control in general; and the data remains quite limited and incomplete, such that we cannot confidently say that the burden of malaria has been falling on average. We can imagine that a malaria scholar, with more context than we have on the strengths and weaknesses of different data sets and the histories of malaria control in different areas, could have a higher degree of confidence in the idea that malaria control (and LLINs in particular) has contributed to major declines in the burden of malaria.
As noted above, ITN distribution appears to have benefits other than reduced mortality, such as reduced anemia (an effect size larger than what we have seen for deworming). In addition, Bleakley 2010 makes a case that reducing the burden of malaria may have a lasting impact on children's development, and thus on their ability to be productive and successful throughout life. This is a similar paper, with similar results, to one of the two major pieces of evidence for the developmental impact of deworming.
Bleakley 2010 analyzes a number of attempts to eliminate malaria in the Americas during the early-to-mid 20th century, focusing on the U.S., Brazil, Columbia, and Mexico. He concludes:
There are good reasons to be cautious in using this study as evidence relevant to ITN distribution:
That said, we believe the paper merits some weight on the question of developmental benefits, because:
Bleakley also finds effects on school enrollment that vary by country.41
It appears that there has been a shift in emphasis over the last several years from targeted coverage (aiming primarily to cover children under five and pregnant women with ITNs) to universal coverage (aiming to protect everyone in a community with ITNs).
The 2004 Cochrane review discussing the impact of ITNs on under-5 mortality (discussed above) appears to advocate primarily for coverage of children under five,45 and as of 2006 this seemed to be the focus of the Roll Back Malaria Partnership, the United Nations Millennium Development Goals, and the US President's Malaria Initiative as well.46 However, in 2007 the World Health Organization issued a recommendation for universal coverage that appears to have been an explicit change in position.47
We did a brief investigation of the arguments for targeted vs. universal coverage, because we wondered whether the Against Malaria Foundation's focus on universal coverage was justified. It seemed to us that if the main benefit of ITNs is in reducing mortality for children under five, then targeting children under five could achieve most of the benefits of universal coverage, for a fraction of the cost. On the other hand, there is a potential argument for universal coverage based on the possibility that universal coverage will be more likely to have community-level effects.48
Our investigation consisted of:
Our conclusions are:
The scholars we spoke with also pointed us to papers attempting to model malaria transmission mathematically.
We asked one scholar whether there were any prominent papers in this category making the opposite argument (that community-level effects are likely to be insignificant) and he replied that he did not know of any.62
We do not find the evidence for community-level impact to be conclusive, but we believe that the best interpretation of the available evidence suggests at least some community-level impacts, consistent with the consensus of the scholars we spoke to and the World Health Organization.
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).
We provide a spreadsheet73 that estimates the (a) cost per life saved, (b) cost per person protected per year, and (c) cost per child under 14 protected per year. Cells highlighted in green represent particularly debatable and/or variable parameters; readers can change these (or any other figures) to see how the outcomes are affected.
Our analysis is relatively simplified and unlikely to capture all of the key issues. Some key assumptions and choices made in our model:
LLINs are assumed to last 2.22 years on average, consistent with the decay model discussed above. We assume that this decay model accounts for a substantial amount of the extent to which LLINs are lost, not delivered, or discarded. We provide a less optimistic estimate where LLINs are assumed to last 1 year on average (note that the evidence on ITN effectiveness is generally limited to a time frame of one year); we provide a more optimistic estimate where LLINs are assumed to last 3 years on average (this could be warranted if Against Malaria Foundation distributions result in fewer lost/undelivered/discarded LLINs).
Two more general notes on the limitations to cost-effectiveness analysis such as this:
Our best-guess estimate comes out to about $2,500 per life saved using the total cost per net and about $2,300 per life saved using the marginal cost pet net (see details on total versus marginal costs per net in our our updated AMF review). This does not include other benefits of ITNs. We also show the number of children under 14 who are protected for each life saved, since protection may yield non-mortality-related benefits comparable to those of deworming, and we provide some rows that account for this additional benefit in order to allow more intuitive comparisons between the two interventions.
We also provide reference points for conversions to the cost per disability-adjusted life-year (DALY), a common metric in public health. We have found this metric to add more confusion than clarification,78 but we provide this information for those who find it helpful. Note that our cost per DALY figures are based only on lives saved and do not account for other benefits.
As discussed above, we have what we believe to be fairly comprehensive data on the number of LLINs distributed to each country over the last several years. By combining this with different versions of the decay function discussed above and different estimates of the population at risk for malaria, we have estimated how many LLINs would still be needed to achieve 100% (theoretical) coverage, for each country as of the end of 2011 and 2012.79
Regardless of which version of the calculation we use - even when assuming that LLINs remain 100% in use for 3 years after distribution and when using the lowest "population at risk" figures we have - we see substantial gaps in LLIN coverage. Six of the seven countries emphasized by AMF in its discussion of room for more funding - have a gap of ~1.1 million LLINs or more, thus each of these gaps would take $5.5+ million (using Against Malaria Foundation costs per LLIN distributed) to close. The exception is Malawi, where the data used in the model indicates that the gap has been more than filled (AMF believes gaps remain in at least some areas of the country80). When examining the full list of countries listed by AMF, adding up the smallest modeled LLIN gap for each country (excluding the "negative gap" in Malawi) results in a total LLIN gap of over 63 million, or over 12 million excluding the estimated 51 million LLINs needed in Nigeria (thus over $60 million would be needed to close the non-Nigeria gap).
Our coverage analysis81 extends back to 2006 (using delivery data since 2004), showing a picture of fairly persistent LLIN gaps.
"In Africa, malaria accounts for an estimated 25% of all childhood mortality below age five, excluding neonatal mortality (WHO 2003)." Lengeler 2004a, Pg 2.
"Human infection begins when the malaria vector, a female anopheline mosquito, inoculates plasmodial sporozoites from its salivary gland into humans during a blood meal. The sporozoites mature in the liver and are released into the bloodstream as merozoites. These invade red blood cells, causing malaria fevers. Some forms of the parasites (gametocytes) are ingested by anopheline mosquitoes during feeding and develop into sporozoites, restarting the cycle." Jamison et al. 2006, Pg 413.
"Most malaria infections cause symptoms like the flu, such as a high fever, chills, and muscle pain. Symptoms tend to come and go in cycles. One type of malaria may cause more serious problems, such as damage to the heart, lungs, kidneys, or brain. It can even be deadly." WebMD, "Malaria: Topic Overview."
See Jamison et al. 2006, Pg 416, Table 21.3 for estimates of cases of hearing impairment, visual impairment, epilepsy, etc. caused by malaria.
"Using mosquito nets as a protection against nuisance insects was practiced in historical times (Lindsay 1988). During World War II, Russian, German, and US armies treated bed nets and com- bat fatigues with residual insecticide to protect soldiers against vector-borne diseases (mainly malaria and leishmaniasis) (Curtis 1991). In the late 1970s, entomologists started using synthetic pyrethroids: their high insecticidal activity and low mammalian toxicity made them ideal for this purpose.
In the 1980s, studies of ITNs showed that pyrethroids were safe and that ITNs had an impact on various measures of mosquito biting (such as the proportion of mosquitoes successfully feed- ing on humans and the number of times a mosquito bit humans in one night). These studies showed that pyrethroids worked by both repelling and killing mosquitoes. In addition, researchers determined optimal doses of various insecticides with different materials (Curtis 1991; Curtis 1992a; Curtis 1996; Lines 1996; Rozendaal 1989a). The cost-effectiveness of ITNs has also been demonstrated (Goodman 1999; Hanson 2003)." Lengeler 2004a, Pg 2.
See "Abbreviations" - World Health Organization, "World Malaria Report (2010)," Pg ix.
The pyrethroid insecticide permethrin is a synthetic molecule similar to natural pyrethrin, which comes from a species of chrysanthemum. Because it poses minimal toxic risk to humans, Olyset is particularly valuable where babies and small children are concerned." Sumitomo Chemical, "Olyset Net."
"WHO recommendations for vector control are the following:
GiveWell, "Summary of ITN RCTs."
"The remaining 22 trials, including 1 trial that is currently unpublished, met the inclusion criteria for this review. These trials are described below." Lengeler 2004a, Pg 6.
"The summary rate difference, which expresses how many lives can be saved for every 1000 children protected, was 5.53 deaths averted per 1000 children protected per year (95% CI 3.39 to 7.67; Analysis 1.2). I performed a regression analysis of the natural logarithm of the rate difference on the entomological inoculation rate and could not ﬁnd a trend (r^2 = 0.52, F = 3.2 on 1,3 degrees of freedom, P = 0.2). In contrast to protective efﬁcacies, the risk differences seemed to have a tendency towards a higher effect with a higher entomological inoculation rate. This apparent paradox is because the baseline mortality rates are higher in areas with high entomological inoculation rates." Lengeler 2004a, Pg 9. Note on the entomological inoculation rate: “The intensity of malaria transmission measured by the frequency with which people living in an area are bitten by anopheline mosquitoes carrying sporozoites. This is often expressed as the annual entomological inoculation rate (EIR), which is the number of inoculations of malaria parasites received by one person in one year.” World Health Organization, “Guidelines for the Treatment of Malaria,” vii.
"The impact of ITNs on malaria-speciﬁc death rates was looked at only brieﬂy because of the problems using verbal autopsies in determining malaria deaths. In the two trials for which the data were available, the percentage reduction in malaria-speciﬁc mortality was similar or smaller than the percentage reduction in all-cause mortality: 14% (versus 23%) for Gambia (D’Alessandro), and 22% (versus 18%) for Ghana (Binka). One interpretation is that malaria-speciﬁc death rates were not reﬂecting the true impact of ITNs on mortality (since a much higher speciﬁc impact would have been expected)." Lengeler 2004a, Pg 9.
"The summary rate difference, which expresses how many lives can be saved for every 1000 children protected, was 5.53 deaths averted per 1000 children protected per year (95% CI 3.39 to 7.67; Analysis 1.2)." Lengeler 2004a, Pg 8. We have confirmed with the author that this figure is based on an "intention to treat" analysis, e.g., "protected" refers to children in the treatment group, not to children who were confirmed to own or use ITNs.
"Four out of the ﬁve trials that measured splenomegaly were carried out in areas with stable malaria (Appendix 15 and Appendix 16). Because the exception was one trial carried out in Thailand whose weight is very small (only 2.6% in the relevant comparison) (Thailand (Luxemberger)), I did not carry out a subgroup analysis. Splenomegaly was signiﬁcantly reduced for both types of controls: there is a 30% protective efﬁcacy when controls were not using nets, and a 23% protective efﬁcacy when the control group used untreated nets." Lengeler 2004a, Pg 9.
"Only one trial examined severe malarial disease as an outcome Kenya (Nevill). The trial used passive and hospital-based case as- certainment, and observed a 45% (cluster-adjusted 95% CI 20 to 63) reduction in the frequency of severe malaria episodes follow- ing the introduction of ITNs (Appendix 4)." Lengeler 2004a, Pg 8.
"Uncomplicated clinical episodes:
The trial results are available in Appendix 5 for no nets controls and in Appendix 6 for untreated nets controls. A summary of the main ﬁndings for protective efﬁcacies is available in Appendix 7; conﬁdence intervals were not calculated as this analysis includes both cluster and individually randomized controlled trials. No risk or rate differences were calculated because the denominators were not uniform and the sensitivity of the reporting systems of the different trials is likely to have varied considerably. Three ﬁndings can be highlighted.
Lengeler 2004a, Pg 9.
The results are available in Appendix 8 for no nets and in Appendix 9 for untreated nets controls. The results for both groups are summarized in Appendix 10; conﬁdence intervals were not calculated as this analysis includes both cluster and individually randomized controlled trials. Two points can be highlighted from these results.
Lengeler 2004a, Pg 9.
The results are shown in Appendix 11 for no nets and Appendix 12 for untreated nets controls. This outcome was only assessed for trials in areas of stable malaria, where parasitaemia does not necessarily lead to a clinical episode, and where parasitaemia cut- offs are useful to deﬁne disease episodes. Five trials measured this outcome: four used 5000 trophozoites/ml as the cut-off, while the ﬁfth trial used an age-speciﬁc cut-off (Kenya (Phillips-Howard)). The protective efﬁcacy was 29% for the two trials in which the control group did not have nets, and was 20% for the three trials in which controls had untreated nets." Lengeler 2004a, Pg 9.
"Three trials carried out with ITNs have demonstrated a positive impact on anthropological measurements in children sleeping un- der treated nets.
In The Gambia (Gambia (D’Alessandro)), mean z-scores of weight-for-age and weight-for-height were higher in children from treated villages (-1.36 and -0.98, respectively) than in those from untreated villages (-1.46 and -1.13, respectively). The differences were statistically significant after adjustment for area, age, differential bed net use, and gender (P = 0.008 and P = 0.001, respectively). There was no statistically signiﬁcant difference in me signiﬁcant an z-scores for height-for-age.
In the trial carried out in Kenya (Kenya (Nevill)), infants sleeping under ITNs in the intervention areas had statistically signiﬁcantly higher z-scores for weight-for-age than control infants not under treated nets (analysis of variance allowing for season, gender, and age: F = 21.63, P = 0.03). Mean mid-upper arm circumference z-scores were also statistically signiﬁcantly higher among infants in the intervention communities (analysis of variance allowing for survey, gender, and age: F = 19.0, P = 0.005) (Snow 1997).
In Kenya (Kenya (Phillips-Howard)), protected children under two years of age had a statistically signiﬁcantly better weight-for- age z-score than unprotected children (P < 0.04). No other statistically signiﬁcant differences were measured for other parameters or other age groups, although all z-score differences between intervention and control groups were in favour of the protected group." Lengeler 2004a, Pgs 9-10.
“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 anaemia and fetal loss in all pregnancies but not for clinical malaria or low birthweight.” Gamble et al., Pg 1.
GiveWell, "Summary of ITN RCTs."
GiveWell, "Summary of ITN RCTs."
GiveWell, “Summary of ITN RCTs.”
"To the best of my knowledge there have been no more RCTs with treated nets. There is a very strong consensus that it would not be ethical to do any more. I don't think any committee in the world would grant permission to do such a trial." Christian Lengeler, phone conversation with GiveWell, November 2, 2011.
See World Health Organization, "World Malaria Report (2010)," charts on Pg 13.
"The results presented in this review are from randomized controlled trials where the intervention was deployed under highly controlled conditions, leading to high coverage and use rates. The one exception is Gambia (D’Alessandro), which was a randomized evaluation of a national ITN programme in which the intervention deployment was not as good as in the other trials. Therefore, the bulk of data in this review describe impact under ideal trial conditions (efﬁcacy) rather than impact under large-scale programme conditions (effectiveness). While the difference between efﬁcacy and effectiveness is likely to be small for certain medical interventions (such as vaccination or surgery), it can potentially be large for preventive interventions such as ITNs.
Some of the consequences of moving from a scientiﬁc trial towards a large-scale programme is illustrated by the results of the two mortality trials carried out in The Gambia. The ﬁrst trial was carried out under well-controlled implementation conditions, with a high coverage rate in the target population (Gambia (Alonso)). Unfortunately it was not randomized and hence not included in the present analysis. The second one was the evaluation of a national impregnation programme carried out by primary health care personnel and which faced some operational problems (leading, for example, to a lower than expected insecticide dosage) and a lower coverage rate (around 60%) of the target population (Gambia (D’Alessandro)). The difference of impact between the two studies is important: the ﬁrst trial achieved a total reduction in mortality of 42%, while the protective efﬁcacy in the second trial was 23%. It is not clear whether the difference in the baseline mortality rate (42.1 versus 24.3 deaths per 1000 in the control group) played a role in this difference of impact." Lengeler 2004a, Pg 10.
"In reviewing household surveys that provide the most recent results available on ITN coverage for 27 malaria-endemic countries between 2003 and 2009, it was evident that relatively low propor- tions of households own an ITN (median 16%, lower quartile 5%, upper quartile 45%); only 7 surveys were conducted during the massive expansion of ITN programmes from 2008 to 2010. However, within all surveys, a high proportion of available nets appear to be used (approximately 80%) assuming that one net can cover two people (Fig. 4.6a). Some countries such as Madagascar (2008) and Rwanda (2008) have higher rates of use than others. These results are consistent with previous analyses which suggest that the main constraint to enabling persons at risk of malaria to sleep under an ITN is lack of availability of nets (3). " World Health Organization, "World Malaria Report (2010)," Pg 23.
World Health Organization, "World Malaria Report (2010)," Table 4.2, Pg 19.
The assumption of 1.8 people covered per ITN is based in data from the Against Malaria Foundation’s distribution in Malawi: “In the last pre-distribution survey, there were 26,385 sleeping spaces (47,824 people) in the area and 6,326 useable nets. There were fewer nets in Dedza than in Ntcheu. In total they found that on average 1 net is required to cover 1.8 people (some people sleep alone; others share sleeping spaces).” GiveWell, “Notes from Site Visit with Concern Universal in Malawi (October 2011),” Pg 2.
World Health Organization, "World Malaria Report (2010)," Pg 22.
Excluding Rwanda, Democratic Republic of the Congo and Madagascar (>100% implied usage) as well as Swaziland (2% coverage, 0% usage) and Namibia (15% coverage, 6% usage).
GiveWell, "Summary of ITN RCTs."
It does seem possible that the surveys used for the above analysis are less prone to over-reporting than the surveys done in the small-scale studies, because the latter were likely done in the context of ITN promotion programs whereas the analysis above relies on large-scale surveys covering a large number of topics (full surveys are available via Measure DHS). On the other hand, the intensiveness of the interventions in the small-scale studies may have meant more accurate data collection and/or a higher ratio of actual (correct) usage to reported usage.
Bleakley 2010, abstract.
"How realistic is the assumption that areas with high infection rates benefited more from the eradication campaign? Mortality and morbidity data indicate drops of 50 to 80 percent in the decade after the advent of the eradication efforts. Such a dramatic drop in the region’s average infection rate, barring a drastic reversal in the pattern of malaria incidence across the region, would have had the hypothesized effect of reducing infection rates more in highly infected areas than in areas with moderate infection rates. Data on malaria cases by Colombian departments allow us to examine this directly. The decline in malaria incidence as a function of intensity prior to the eradication campaign is found in panel B of Figure 1. The basic assumption of the present study, that areas where malaria was highly endemic saw a greater drop in infection than areas with low infection rates, is borne out. (Similar results are seen for US and Mexican states. Data for Brazilian states were not available.)
Finally, the timing of the eradication campaign should induce variation in childhood malaria infection that has a marked pattern across year-of-birth cohorts. The present study considers the effects of childhood malaria infection on later- life outcomes, so it is useful to characterize childhood exposure to an eradication campaign. This is shown in Figure 2. Consider a campaign that starts in year zero and takes effect instantaneously. Cohorts born after this date will be exposed to the campaign for their entire childhood. On the other hand, those cohorts who were already adults in year zero will have no childhood exposure to the campaign, while the “in-between” cohorts will be partially exposed during childhood, as shown in Figure 2. I exploit this timing in two ways. First, in Section III, I compare the “born after” cohorts to the “already adult” cohorts by taking differ- ences across these cohort groups. Second, in Section IV, I use the functional form of childhood exposure in estimation using data for all cohorts. (I discuss some alternative functional forms in Section IV.B.)
These four factors (the external origin of the campaigns, the quick reduction of malaria that followed, the use of nonmalarious areas for comparison, and the differential incidence of eradication benefits across cohorts) combine to form the research design of the present study." Bleakley 2010, Pgs 8-9.
See Bleakley 2010, Figure 4, Pg 26.
See Bleakley 2010, Appendix III, Pg 40, for the full list of controls by country.
"Mixed results are found for years of education, in contrast with consistently positive effects of malaria eradication on income and literacy. Furthermore, in no country can the change in income be accounted for by the change in years of schooling. These facts are in no way discordant with the economic theory of schooling, which compares returns with opportunity costs. Childhood health plausibly raises both, leaving an ambiguous effect on the optimal time to spend in school. This combination of results, interpreted with simple price-theoretic reasoning regarding the education decision, show that we should be cautious in using changes in time in school as a sufficient statistic by which development and health policies are evaluated." Bleakley 2010, Pg 35.
Kilian et al. 2010.
"An approximate extrapolation to the current population of children under ﬁve years of age at risk for malaria in sub-Saharan Africa (14% of approximately 480 million population at risk, or 67 million children) indicates that approximately 370,000 child deaths could be avoided if every child could be protected by an ITN." Lengeler 2004a, Pg 10.
"The Roll Back Malaria Partnership, the United Nations Millennium Development Goals, and the US President's Malaria Initiative have set a target of at least 80% use of ITNs by young children and pregnant women (the people most vulnerable to malaria) by 2010." Killeen et al. 2007, Pg 1258. Note that this paper was "received December 22, 2006."
The WHO/GMP calls upon national malaria control programmes and their partners involved in insecticide-treated net interventions to purchase only long-lasting insecticidal nets (LLINs). LLINs are designed to maintain their biological efficacy against vector mosquitoes for at least three years in the field under recommended conditions of use, obviating the need for regular insecticide treatment.
In order for their full potential to be realized, LLINs should be deployed as a vector control intervention. WHO/GMP, therefore, recommends full coverage of all people at risk of malaria in areas targeted for malaria prevention with LLINs." World Health Organization, "Insecticide-Treated Mosquito Nets: A WHO Position Statement (2007)," Pg 1.
There is a distinction between individual-level effects (protection of the person sleeping under the net, due to blockage of mosquitoes) and community-level effects (protection of everyone in communities where ITN coverage is high, due to reduction in the number of infected mosquitoes, caused either by mosquitoes' being killed by insecticide or by mosquitoes' becoming exhausted when they have trouble finding a host).
Christian Lengeler, phone conversation with GiveWell, Nov. 2, 2011.
GiveWell, "Summary of ITN RCTs."
"In late 1996, the villages in Asembo were randomized into ITN (intervention) and control villages … for two years, 1997 and 1998, people in half of the villages (intervention villages) in Asembo had access to properly treated bed nets and half (control villages) did not. Periodic spot checks during this period showed that few (<3%) nets were sold or moved outside the study area, although adherence to net use, measured as the proportion of study participants directly seen to be sleeping under nets during early morning observational surveys, was usually approximately 70% … Although the study area is divided into villages with approximate boundaries as shown in Figure 1A, these are social constructs that do not reflect variation in population density … The 300-meter interval for the main exposure variables was based upon the observation that this distance range divides the number of compounds of each type into approximately equal quartiles (Table 1). All distance calculations were done on the basis of intent to treat; all compounds in ITN villages were assumed to have ITNs and all compounds in control villages were assumed to lack ITNs." Hawley et al. 2003, Pg 121.
"… Compounds in control villages that are ≥900 meters from the nearest ITN village served as the comparison group for these analyses. A total of seven dichotomous variables were created that contained all other compounds. For control villages, we created three variables for compounds that were 0–299, 300–599, or 600–899 meters from the nearest ITN compound. For ITN villages, we created four variables for compounds 0–299, 300–599, 600–899, and ≥900 meters from the nearest control compound. The intent of this analysis was to allow us to illustrate spatial patterns of effect in a straightforward way; however, the cost of this approach was some loss in statistical power. These distance categories approximate compound distribution by quartiles as shown in Table 1 … The effect of the primary geographic exposure variable, distance to nearest compound of different type, is illustrated in Figure 2, which shows the effect of each of seven different exposure categories on five malaria-related outcomes, as well as geohelminth infection. For geohelminth infection, no effect of ITN use or distance is apparent. In contrast, a protective effect of living in ITN villages (stippled area of Figure 2) is apparent at all distance categories for all-cause mortality of children 1–59 months of age and for high-density parasitemia, anemia, and hemoglobin level … The overall pattern of effects is similar for all five malaria-related outcomes: protective effects are observed within the ITN compounds, with a similar level of protection seen in control compounds located within 300 meters of intervention compounds; these effects are statistically significant for the morbidity measures most sensitive to changes in transmission levels: anemia and hemoglobin level … Results of tests of trend reflect the patterns visible in Figure 2 for clinical malaria (odds ratio [OR] = 0.92, 95% confidence interval [CI] = 0.75, 1.12, P = 0.38), high-density parasitemia (OR = 0.89, 95% CI = 0.78, 1.01, P = 0.08), moderate anemia (OR = 0.78, 95% CI = 0.69, 0.89, P = 0.0001), hemoglobin level regression coefficient (OR = 0.18, 95% CI = 0.06, 0.31, P = 0.0048), and child mortality (hazard ratio = 0.94, 95% CI = 0.90, 0.98, P = 0.002). For all of these malaria-related outcomes, trends are in the direction indicating greater protection in compounds closer to intervention villages, with strongly significant trends seen for mortality, anemia, and hemoglobin level. For geohelminth infection, no trend was observed (OR = 1.09, P = 0.47)."
Hawley et al. 2003, Pgs 123-125.
"This community effect on nearby compounds without nets is approximately as strong as the effect observed within villages with ITNs." Hawley et al. 2003, Pg 121.
"studies from various parts of Africa and Papua New Guinea indicate the presence of a beneficial community effect (we propose use of this term rather than the less descriptive mass effect) on malaria transmission [references 1-6], severe malaria [reference 7] and mortality [reference 8] in children. One study, in contrast, yielded no evidence for either beneficial or harmful community-wide effects. [reference 9]" Hawley et al. 2003, Pg 121.
We looked up reference 9 and confirmed that it discusses only transmission: "In The Gambia, the use of permethrin-treated bed nets has led to a reduction in morbidity and mortality from malaria in children. However, no clear evidence has been found for a 'mass-killing effect' on the mosquito vectors as a result of this intervention. Two further entomological studies to investigate this phenomenon have been carried out. In one study, 20 villages were paired so that bed nets in one member of each pair were treated with permethrin. In the other, a cross-over design was used in which treated and untreated bed nets were exchanged between 2 villages. Longevity, biting rate and resting density of the malaria vector population and sporozoite rates were assessed in both studies. Malaria vectors were equally abundant and long-lived, and as likely to be infective, in villages with treated bed nets as in those with untreated nets. However, a clear reduction in the density of the indoor-resting population of mosquitoes in rooms with treated bed nets was found, probably reflecting the excito-repellency of the insecticide. This study confirmed that, in The Gambia, the protection against death and morbidity from malaria seen in children using treated bed nets must be due primarily to personal protection rather than to a 'mass-killing effect' on the mosquito vector population at a village level." Quinones et al. 1998, abstract.
Gamble et al. 2006, Pg 14.
"An important paper that had some influence in the political debate about mass distribution (as opposed to distribution to infants and pregnant women only) was:
Preventing childhood malaria in Africa by protecting adults from mosquitoes with insecticide-treated nets. Killeen GF, Smith TA, Ferguson HM, Mshinda H, Abdulla S, Lengeler C, Kachur SP. PLoS Med. 2007 Jul;4(7):e229." Thomas Smith, email to GiveWell, November 8, 2011.
Killeen et al. 2007, Pg 1246. The paper includes a spreadsheet with the full specification of its model.
See Smith et al. 2009, Table 1, Pg 514. Note that the higher the existing level of ITN coverage (column headings), the lower the additional amount of ITN coverage needed (figure in the cell minus figure in the column heading) to reach the specified target. For example, at a PfPR of 50% and a goal of reducing it to 1% (10th row, 4th-6th columns), one would need to go from 0% to 71% effective coverage (71% absolute change), or from 10% to 77% coverage (67% effective change), or from 20% to 81% effective coverage (61% effective change).
"Holden Karnofsky: Do you know of any papers or scholars arguing the opposite, that community-level effects are negligible and/or that universal coverage has little value-added above and beyond covering pregnant women and children under five?
Thomas Smith: I don't." Thomas Smith, phone conversation with GiveWell, Nov. 8, 2011.
"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.
GiveWell, "Cost-Effectiveness Analysis for LLIN Distribution Updated."
"The summary rate difference, which expresses how many lives can be saved for every 1000 children protected, was 5.53 deaths averted per 1000 children protected per year (95% CI 3.39 to7.67; Analysis 1.2)." Lengeler 2004a, Pg 8. We have confirmed with the author that this figure is based on an "intention to treat" analysis, e.g., "protected" refers to children in the treatment group, not to children who were confirmed to own or use ITNs.
“The summary rate difference, which expresses how many lives can be saved for every 1000 children protected, was 5.53 deaths averted per 1000 children protected per year (95% CI 3.39 to 7.67; Analysis 1.2). I performed a regression analysis of the natural logarithm of the rate difference on the entomological inoculation rate and could not ﬁnd a trend (r 2 = 0.52, F = 3.2 on 1,3 degrees of freedom, P = 0.2). In contrast to protective efﬁcacies, the risk differences seemed to have a tendency towards a higher effect with a higher entomological inoculation rate. This apparent paradox is because the baseline mortality rates are higher in areas with high entomological inoculation rates." Lengeler 2004a, Pg 8.
See penultimate section of our 2012 blog post on the subject.
See our blog posts on the topic:
GiveWell, "LLIN Gap Analysis (2012)." Note about the data on which our analysis is based: “This map is a theoretical model based on available long-term climate data. It has a resolution of about 5x5 km. Although it is reasonably accurate, it is not based on actual malaria data and may not reflect the real malaria status. It shows the theoretical suitability of local climatic, and therefore the potential distribution of stable malaria transmission in the average year. Please note that climatic conditions, and therefore malaria transmission, vary substantially from one year to the next. Malaria control activities can also dramatically alter the malaria transmission situation.” Mapping Malaria Risk in Africa, “Information on Maps.”
"We have approved a distribution of 250,000 nets in the districts of Balaka and Dedza in Malawi. The distribution would take sleeping space coverage levels from 30-60% (the level is currently unknown) to 90% and above." Against Malaria Foundation, "Recently Approved Distributions and Others Being Assessed."
GiveWell, "LLIN gap analysis," Sheet "Basic gap analysis."