Estimating Equivalent Coverage Years for Long-Lasting Insecticide-Treated Nets (LLINs) – November 2020 version | GiveWell

We have published more recent information on our approach to estimating coverage years. See this section of our report on insecticide-treated nets.

Published: November 2020

Measuring Net Durability

Post-distribution net loss occurs for multiple reasons: attrition (i.e., nets were discarded due to damage, appropriated for other uses, given away, moved, or stolen), extensive holes in the net that make it permeable to mosquitoes, and decay of the net's insecticide component to the point that it is no longer effective. This section summarizes the quality control and field testing procedures used to evaluate net durability outcomes, which inform our estimate of equivalent coverage years.

LLIN Product Qualification

The World Health Organization's Pesticide Evaluation Scheme (WHOPES) maintains product testing standards for qualifying bednets for purchasing and field use. The full list of LLINs that meet WHO's prequalification standards and are eligible for procurement is available here. To date, all of the brands and types of bednets that AMF has procured appear on WHO's prequalified product lists and meet WHO's quality requirements.

However, many of the quality control tests for WHO bednet prequalification are lab-based rather than long-term and field-based, and it is unclear how this qualification translates into estimated net lifespan in a 'typical use' environment. Testing requirements do not necessarily demonstrate that all brands of approved LLINs are identical in quality. The most vetted brands of LLINs pass three phases of testing, including long-term testing that includes three years of field monitoring for insecticide performance, and passing this test results in receiving a full recommendation from WHO and being named a 'reference class' product. Products that aspire to become reference class nets may receive an interim recommendation from WHO based on passing the first two phases of the full qualification process. Other 'generic' brands of nets receive a WHO recommendation based on equivalent performance to a WHO-recommended product with the same chemical and physical specifications in the first phase of qualification (lab tests for textile strength and chemical analysis of the insecticide component).

Field Durability Monitoring

In 2011, WHO established field durability monitoring guidelines for LLINs. The President's Malaria Initiative (PMI) also maintains LLIN field durability monitoring advice for practitioners and a database of field durability sites. WHO released further instructions for collecting field durability data and using it to calculate net survival in 2013.

Under current guidelines, a full battery of LLIN durability monitoring tracks four outcomes: attrition (survivorship), physical integrity, insecticidal activity, and residual insecticide content. Attrition and physical integrity are the easiest outcomes to measure, requiring no special equipment, and our impression is that they are the most commonly measured outcomes. Not all monitoring studies have the resources to track all potential outcomes. For optimal monitoring, WHO recommends a prospective monitoring design that tags a group of nets for follow-up at several predetermined points in time.

Attrition

The attrition rate is the proportion of cohort nets that is no longer present or being used as intended at each point of follow-up. This rate grows cumulatively over time. There are several reasons why nets may be absent at follow-up. Households may have discarded nets due to damage; appropriated them for other uses; or reported them given away, moved, or stolen.

Attrition is likely to be the most important factor determining net lifespan. The least effective net is one that isn't available for use. In addition, attrition heavily influences assessment of the condition of surviving nets, since it tends to remove the most damaged nets from the study cohort over time, while only remaining nets can be evaluated for physical condition. Attrition depends on subjective household decisions about when and why to dispose of nets, and these decisions don't necessarily align with the end of a net's useful lifespan. The visible, physical condition of a net influences decisions about whether to discard it, but households may discard nets that still have protective efficacy, including nets with only a few holes. Other households may hang onto nets that are in poor condition well beyond their expiration date. The household's net supply also influences its decisions to give away nets.

Net attrition is somewhat difficult to measure, and monitoring data may be biased. The expectation that households' net usage will be monitored may cause them to change their behavior and keep used nets for longer than unobserved households. Prospective monitoring studies that follow the same group of households over time are able to track a consistent cohort of nets and reduce difficulties with recall, but these studies likely affect behavior, and we expect that, by reducing net disposal and reallocation, they may underestimate the role of attrition relative to damage in assessing net survivorship. Retrospective studies that follow up with households once at a designated point after distribution don't suffer the same behavioral effects, but they may also suffer from bias if researchers don't know how many nets surveyed households originally received. In either case, we can't verify the true reason nets are absent, and recall and reporting biases may affect self-reports of the causes of missing nets.

Physical integrity

Physical integrity of LLINs refers to the durability of the net's textile. Nets eventually develop holes that may allow mosquitoes to pass through and feed. WHO recommends monitoring physical integrity by counting holes of different sizes in the net's fabric at each follow-up point and calculating a Proportionate Hole Index (pHI) value that relates to the total surface area of holes in the net. WHO divides nets into three condition categories based on pHI, which facilitates comparison of net condition across sites:

1. Good (pHI=0-64): no reduction in efficacy.
2. Serviceable (pHI=65-642): damaged but still significantly more effective than no net.
3. Too torn (pHI=643+): doubtful protective efficacy and in need of replacement.

Our impression is that these net condition cutoffs are backed by some evidence of the extent of mosquito feeding inhibition at different levels of surface damage, but we have not vetted WHO's sources for its recommendation in detail. The WHO guidelines indicate that the pHI cutoff for a 'too torn' net was set conservatively based on the evidence.

Physical integrity measurements relate to attrition because nets may be discarded over time due to visible wear. Physical condition can only be measured for remaining nets, so pHI measurements may decrease early in a distribution cycle as nets become damaged and rebound later in the cycle as households discard nets in poor condition.

Insecticide content and activity

LLINs contain a durable pyrethroid insecticide reservoir that is either incorporated within or coated onto the net fibers. This insecticide treatment makes up a large part of a net's protective efficacy. In our insecticide resistance adjustment, we estimate that in net RCTs, the insecticide component was responsible for 73% of the protective effect, though we'd expect that the role of insecticide relative to the physical barrier has since decreased for standard LLINs as insecticide resistance has increased. The goal of LLIN insecticide monitoring is to determine whether the net's insecticide continues to inhibit mosquitoes effectively over time (i.e., to determine bioefficacy). Insecticidal activity is typically measured by performing WHO cone bioassay or tunnel tests on a small sample of nets collected from surviving nets. The cone bioassay tests expose susceptible (non-resistant to insecticide) mosquitoes to sections of the net for a few minutes and subsequently measure the degree of mosquito knock-down and mortality to test insecticide bioavailability. WHO grades "optimal" insecticide performance as causing at least 80% mortality or at least 95% knock-down in cone or tunnel tests after three years of use. Testing for residual insecticide content in nets is a supplementary measure that helps with interpretation of the bioefficacy results, but bioefficacy results take precedence, since bioefficacy isn't directly correlated with insecticide content. Despite the importance of insecticidal activity for protective efficacy, WHO doesn't currently recommend factoring insecticide performance into estimates of median net lifespan. There are several reasons for this decision:

• Qualification trial methodology for 'reference class' nets requires that 80% of nets exhibit optimal performance on bioassay tests after three years in the field. This means that 'good' insecticide performance is baked into the LLIN qualification process, so we may expect that insecticide isn't the limiting performance factor.
• The current methodology for measuring insecticide performance isn't ideal and can't test all nets enrolled in a trial. Bioassay tests are expensive and require removing a subset of nets from the field to a lab, so the sample size is small (usually 30-50 nets per time point). Therefore, the results have higher variance.
• There is not yet a simple test for insecticide residue in nets that is ready for field use. There also isn't a simple connection between insecticide performance and the amount of insecticide remaining in the net. While insecticide content does appear to decay rapidly in LLINs over time, nets can still perform well in bioassays with low insecticide residue.
• It is unclear where to place the threshold for minimally acceptable insecticide performance. Studies sometimes use minimum criteria of 50% mortality or 75% knockdown, but these were not ratified by WHO as of the publication of this report in 2013.

WHO's 2013 decision not to factor insecticide performance into median lifespan estimates was intended to be provisional, with the option of later incorporating information on insecticide.

Note that the above describes quality control and testing procedures for standard LLINs that contain a pyrethroid insecticide. This report doesn't include analysis of the next generation of LLINs that include the chemical piperonyl butoxide (PBO) in addition to pyrethroid insecticide or other next generation nets with dual active ingredients. PBO durability is an active research question, and it's possible that PBO is less durable than standard insecticide treatments. We plan to look at PBO net insecticide durability separately in the future.

Differences between today's LLINs and nets used in RCTs

GiveWell's cost-effectiveness analysis of interventions that distribute bednets for the prevention of malaria relies on evidence from randomized controlled trials (RCTs) using conventionally treated nets (CTNs) to calculate the effectiveness of nets at averting child mortality. However, the CTNs used in these trials differ in key ways from the long-lasting insecticide-treated nets (LLINs) used today, namely in how they are impregnated with insecticide, when they are replaced, and what information and encouragement is given to recipients about the care and use of the nets. In order to accurately estimate the effectiveness of current net distributions at averting child mortality, we need to understand how net survival compares between LLINs and nets used in the RCTs that inform our estimate of net effectiveness at averting child mortality.

Unfortunately, net trials provide limited information on net durability, and trial conditions probably affected net coverage and maintenance behaviors in ways that would not apply to other contexts. In order to evaluate the nets used in trials, we have given the most weight to information about net distribution protocols from Phillips-Howard et al. 2003, a trial included in a Cochrane meta-analysis of the impact of insecticide-treated nets on mortality and malaria morbidity. Phillips-Howard et al. 2003 is the bednet mortality trial that makes up the majority of the child mortality effect estimate in the Cochrane meta-analysis. Additionally, we have relied on information about technical differences between the types of nets used and reviewed the additional underlying RCTs of the Cochrane child mortality effect estimate for information on net survival and the studies’ distribution protocols.

Based on the somewhat limited information that we have, our understanding is that the nets used in trials likely differed from today's nets in the following ways:

• Insecticide technology. The CTNs (conventionally treated nets) that trials provided were a more primitive type of net with a less durable insecticide treatment than today's LLINs. CTNs are manually treated with insecticide and require frequent retreatment to maintain insecticide content, while LLINs are factory-treated with insecticide that releases over time. The studies included in our mortality estimate maintained a protocol of insecticide retreatment of the CTNs every 6 months to combat insecticide loss, while LLINs don't require retreatment.
• Shorter target use duration. All of the child mortality RCTs included in the 2018 Cochrane meta-analysis lasted for 24 months, while AMF generally funds distributions that take place every 36 months. This difference means that nets in trials were younger on average and thus probably less physically damaged on average than nets distributed today.
• Higher population coverage. Our research indicates that trials likely started with a higher baseline target coverage for the number of nets per person distributed, compared to AMF's target initial distribution coverage rate. In addition, some of the RCTs used in the Cochrane child mortality effect estimate, including Phillips-Howard et al. 2003 and Binka et al. 1996, distributed additional nets during the experiment. Phillips-Howard et al. 2003 reported minimal net attrition rates over 24 months, and another trial reported no reduction in coverage between the first and second year of the trial.
• More intensive training and monitoring. Phillips-Howard et al. 2003 provided subjects with intensive training on net care and use. Researchers provided subjects with extensive training on net use and care, quarterly monitoring visits, and materials for net repair at each monitoring point. Another trial, Nevill 1996, also reported extensive training and support for net recipients. We expect that these experimental conditions may have resulted in less net attrition and better upkeep in trials compared to field distributions, although it's possible that net upkeep is better today due to households having more experience using and caring for nets.

Available literature on LLIN lifespan and field durability

We would ideally like to find a systematic review that aggregates many field studies of net durability across multiple brands of LLINs together into an empirical estimate of an average LLIN lifespan, highlighting possible quality differences between different brands of LLINs. To the best of our knowledge, this type of work is not available to date. We have found two sources that provided some particularly helpful synthesis of the available information. While the methodology is somewhat limited, they suggest that median lifespan for an LLIN is around two years. Both sources find that net lifespan is variable across contexts.

Synthesis source 1: Bhatt et al. 2015

Bhatt et al. 2015 is a mathematical modeling paper that compares data on net access, coverage, and usage from national household surveys to programmatic reports on the number of nets distributed across 40 countries in Sub-Saharan Africa. This study is limited in that it only tracks net attrition over time and not the condition of surviving nets, so it may overestimate functional net survival. This study is also retrospective and depends heavily on the accuracy of administrative data sources to assess net attrition relative to nets distributed. Note that we have not examined the modeling calculations behind the results or vetted the quality of the study in detail.

The main net survival result from Bhatt et al. 2015 finds a median net lifespan of 23 months (95% confidence interval: 20-28 months) across 40 countries in Sub-Saharan Africa between 2011 and 2013, with substantial variation between different countries.

Synthesis source 2: Kilian et al. 2018

Kilian et al. 2018 is a poster presentation summarizing and comparing field monitoring data from the President’s Malaria Initiative (PMI) spanning 24 months post-distribution for five different brands of LLINs distributed in five different countries. Unlike Bhatt et al. 2015, this presentation provides evidence on net condition over time and across different net brands, rather than on attrition only, though it is more limited in terms of breadth of countries and time periods studied.

Kilian et al. 2018 does not present an average lifespan result, but it reports median lifespan estimates for each brand by location. These estimates vary widely—from 1.4 years for the Dawa Plus 2.0 in the Democratic Republic of the Congo to 5.6 years for the same brand in Nigeria. It concludes that differences in results between locations were greater than differences across brands. The study also examined the effectiveness of the LLIN insecticide and found that insecticidal effectiveness was sufficient at most sites 24 months post-distribution.

GiveWell's model of LLIN equivalent coverage years

Using the three key components of net durability (attrition, physical integrity, and insecticide activity), we have estimated the expected survival and protective coverage of LLINs distributed by AMF, relative to the CTNs used in the RCTs that GiveWell relies on to estimate bednet effectiveness for averting child mortality. Our model is available here. Our current best guess is that an LLIN distributed by AMF confers 2.11 equivalent coverage years over 36 months of potential use (before the next distribution round occurs), where one "equivalent coverage year" represents a similar quality of protection to a CTN distributed in one of the bednet RCTs over one year of the trial. This can be interpreted to mean that today's LLINs provide about 30% less coverage and protection per year (when averaged across the three years of a typical distribution) compared to the coverage and protection provided by trial nets per year (averaged across two years). Note that this is a simplification, since our calculations indicate that LLIN coverage declines substantially over the course of 36 months.

Note that this analysis is a simplified model that relies on limited data and does not take into account a number of factors. There is significant uncertainty surrounding our assumptions. Additionally, we frame this input as a performance outcome for a reference class net in an 'average' net distribution, but we understand that durability outcomes may in fact vary substantially across time and space. We provide these simplified estimates (a) for transparency about important assumptions used in our cost-effectiveness analysis and (b) because working on them helps us ensure that we are thinking through as many of the relevant issues as possible.

Below, we explain the key choices and assumptions that we made in our model.

Data Sources

Our current input starts with a durability estimate for Vestergaard's PermaNet 2.0 LLIN, which is based on all field monitoring studies of PermaNet 2.0 that we are aware of that present results compliant with WHOPES monitoring guidelines. We then make rough adjustments for other types of nets that AMF purchases that may have more limited performance data.

Why we chose the PermaNet 2.0 as a reference net

In order to balance having a consistent set of inclusion principles with tractability, we decided to limit the scope of this project and focus primarily on the PermaNet 2.0 (the net which makes up the largest proportion of AMF’s purchases). While we'd ideally have a comprehensive set of durability monitoring data across all available brands of LLINs that might allow us to establish which types of LLINs are the most cost-effective overall, our preliminary research indicated that this would be difficult. Many monitoring studies of LLINs are available, and it would be time-consuming to search out, review, and extract data from all of them. Instead of doing a comprehensive search, we explore some rough comparisons of the PermaNet 2.0 with other brands of nets that AMF purchases in large volumes, particularly the Yorkool LN, below.

We chose the PermaNet 2.0 to serve as a reference net for the following reasons:

• Relevance to AMF's distributions. AMF has purchased significant quantities of both PermaNet 2.0s and Yorkool LNs.
• Extensive data availability. There appears to be a particularly large amount of field monitoring data available for the PermaNet 2.0. Studies are available from several different countries, and multiple studies have long follow-up duration up to 36 months.
• Tractability. Focusing on one key brand of net as a starting point for our model was easier and clearer to execute than other possible sub-divisions of the literature. We expected searching for "PermaNet 2.0" would reliably yield the relevant research published to date with few studies that we needed to filter out. Identifying another filter to use, such as study methodology or duration, would be challenging without first finding and reviewing the majority of published field monitoring studies and likely would also lead to discarding a large amount of information (for example, there are many monitoring studies with fewer than 3 years of follow-up).

The criteria we used for inclusion in our dataset are:

• The study must name the PermaNet 2.0 as one of the nets studied.
• The study must present results from post-distribution field monitoring that captured net performance in real-life conditions. We excluded lab, hut, and wash trials from the evidence base.
• The study must report information on attrition and/or pHI at a follow-up point up to 36 months post-distribution, and it must report results in a way that conforms to WHOPES monitoring guidelines. For example, results that reported only average pHI rather than the proportion of “too torn” nets were excluded. The study does not necessarily have to include a full set of usable outcomes to be included as long as at least one variable is relevant.

In total, our criteria identified 11 monitoring studies. These studies span distributions that occurred between 2005 and 2017 in 10 different countries.

Aggregating data from multiple monitoring surveys

We have averaged the data from the 11 PermaNet 2.0 monitoring surveys that met our inclusion criteria in this spreadsheet. We aggregated the PermaNet 2.0 data by taking a simple average of the proportion of surviving nets and the proportion of surviving nets classified as 'too torn' across all studies at each follow-up interval of 6, 12, 18, 24, 30 and 36 months post-distribution. Results are not available for every time point for every study, so each point-in-time estimate is generally based on fewer than 11 results. This gives a rough average of net degradation for each year post-distribution and allows us to better compare net durability between CTNs and LLINs.

Note that while some nets still survive in serviceable condition 36 months post-distribution, we don't track these nets or include them in our coverage years estimate, since we expect them to be superseded by the next round of net distribution. This is a simplifying assumption; in some cases, surviving nets will affect how long households wait to start using new nets. We adjust for pre-existing nets in a separate parameter in our model.

Calculating equivalent coverage years for the PermaNet 2.0, relative to CTNs used in trials

In order to account for the difference in coverage levels between LLINs in today's mass campaigns and CTNs in trials, we estimate LLIN coverage in terms of "equivalent coverage years" (i.e., years of coverage at a level equivalent to the coverage provided by CTNs in the trials we rely on to estimate benefits). See above for more information on the differences between LLINs and trial nets, which inform these assumptions.

In order to estimate an input for equivalent LLIN coverage years, we need to understand how each facet of net durability compares between LLINs and nets used in the RCTs that inform our estimate of net effectiveness at averting child mortality. Estimated annual mortality benefits from trials should scale with the protective efficacy of the nets provided during the experiments. If we were to use an estimate of how quickly LLINs wear out in absolute terms to calculate coverage duration in our cost-effectiveness analysis of bednets, we would be implying that the nets used in trials remained in good condition and coverage was maintained for the full target population throughout the trial period. This is unlikely to be the case.

We make the following assumptions to compare PermaNet 2.0 LLINs to CTNs used in trials:

• Attrition. We count all measured attrition of LLINs in PermaNet 2.0 monitoring studies, less nets that we estimate were given away and used elsewhere, as lost relative to net coverage years in RCTs. As explained above, it is likely that attrition was minimal or even negative in net trials. As a result, we expect net attrition to be an important point of difference in the level of protection offered between today's field distributions and earlier RCTs.
• Physical integrity. None of the relevant RCTs reported data on holes in nets, so this input is highly uncertain. We expect that LLINs in AMF distributions likely have somewhat more holes on average than CTNs used in trials, because trial nets may have deteriorated more slowly due to increased training, monitoring, repair, and redundancy (due to high target coverage rates under trial conditions). We use a rough guess that nets used in trials took one-third less damage than the average for PermaNet 2.0 nets for each relevant monitoring point up to 24 months post-distribution (when trials ended). This assumption could be wrong if the behavioral effects of monitoring led households to avoid throwing away worn-out nets in RCTs, artificially reducing attrition.
• Insecticide. We do not make adjustments for the effectiveness of the insecticide component of LLINs relative to trial CTNs, based on evidence that average insecticide content for LLINs over a 3-year horizon is similar to CTNs that are fully re-treated every 6 months as specified in trials, as well as evidence that CTNs maintained adequate insecticidal activity over the study period in the one underlying RCT for which data is available. This is an uncertain assumption because it's based on limited evidence that's somewhat challenging to interpret. One study, from Uganda, found that both LLINs and CTNs lose a considerable amount of insecticide over time, with different time profiles—insecticide content in CTNs decays more quickly, and with regular retreatment it would experience frequent peaks and valleys as insecticide degrades and is replenished, compared to a gradual decline of roughly 20% per year in insecticide content for LLINs. Based on data from this paper, we estimate that the differential timing of peaks and troughs in the insecticide content of CTNs roughly balances out over the long run to be equivalent to the average insecticide content of LLINs. We interpret these results cautiously because comparing average residual insecticide content may not translate linearly into comparing insecticidal bioavailability to kill or knock down mosquitoes. However, one RCT collected data on insecticidal activity and found that CTNs performed well across the study period. The available data on insecticide content from RCTs suggest that regular retreatment was reasonably successful at restoring insecticide content, though insecticide performance may have suffered in trials if CTNs were not retreated on time.

We estimate that the PermaNet 2.0 provides 2.27 equivalent coverage years across a 3-year distribution. See our calculations here. In the following sections, we explain how we adjust this figure to reflect how we expect other brands of nets to perform relative to the PermaNet 2.0.

Accounting for differences between net brands

Evidence on quality differences

Many of the other LLINs that AMF has purchased differ in their product specifications (e.g., fabrication, density of the weave, type of insecticide) from the PermaNet 2.0. The evidence on whether we should expect major quality differences between net brands appears to be limited and mixed. As described above, preliminary evidence comparing field performance across several countries suggests that differences between settings may be more important than differences between brands. However, not all net products have faced the same rigor and duration of quality control testing as the PermaNet 2.0 (see here). We are aware of at least two brands of LLIN that received product recommendations from WHO but later had their recommendations revoked over failure to pass field testing and manufacturing defects. (AMF has never purchased nets from either of these brands.)

AMF-specific adjustment for Yorkool LN net quality

AMF has purchased several different brands and types of LLINs over its history. The PermaNet 2.0 and the Yorkool LN have both been purchased frequently over time. The Yorkool LN is of particular interest to us given the relatively high number that AMF has purchased and its status as a 'generic' net product that did not have to undergo field durability testing for WHO approval. If there are quality differences between the Yorkool LN and PermaNet 2.0, these seem the most likely to drive changes in our equivalent coverage years estimate.

We did a literature review of durability data available for the Yorkool LN and found four relevant studies. One study, Rahaivondrafahitra et al. 2017, provided evidence on the durability of both the Yorkool LN and the PermaNet 2.0 after 24 months of use in Madagascar, allowing us to directly compare the two brands. In our head-to-head comparison based on this study, we found that Yorkool nets performed similarly to PermaNet 2.0 on physical survival and performed worse on insecticidal activity.

The additional three studies provide data on Yorkool LN nets, but not PermaNet 2.0. Thus, we compare the data on Yorkool LN nets in these studies to our expectations for how well PermaNet 2.0 would perform on physical integrity and to WHO performance requirements for insecticide. On physical survival, one of these three studies found more nets in serviceable condition (according to pHI) relative to our expectations for PermaNet 2.0, another found somewhat fewer Yorkool nets surviving in serviceable condition, and the third did not report on physical survival. On insecticidal activity, two of the three remaining studies found that the Yorkool LN net passed WHO guidelines for mosquito mortality in cone tests, while one found that the Yorkool LN net failed to meet requirements.

Altogether, the four studies suggest that Yorkool LN performs similarly to PermaNet 2.0 on physical integrity and performs worse on insecticide. However, the evidence on insecticide is difficult to interpret. In the two trials from Madagascar where Yorkool LN performed poorly on insecticide, other brands of nets (including PermaNet 2.0 in the one head-to-head trial) also failed to meet WHO requirements, though Yorkool performed worse than PermaNet 2.0. A possible interpretation of this evidence is that Madagascar is a particularly harsh context for net survival.

Based on this evidence, we calculated a rough effectiveness adjustment for the Yorkool LN relative to the PermaNet 2.0. We currently estimate that the Yorkool LN provides about 15% worse protection than our estimate for the PermaNet 2.0, which equates to 1.93 equivalent coverage years over a 3-year distribution.
Here is a summary of our calculations for the Yorkool net:

• We assume that 40% of the net's protective effect comes from the physical barrier and 60% comes from the insecticide component. Details in footnote.
• In a head-to-head comparison of Yorkool and PermaNet 2.0 in the 2015 Madagascar distribution, we estimate that Yorkool nets performed 24% worse at 24 months post-distribution (calculation here). The physical survival component of the Yorkool nets performed about the same, while the insecticide component performed about 37% worse.
• After assigning 50% weight to the head-to-head comparison results and 50% weight to results from the other relevant literature, the performance adjustment falls to approximately 15% worse than the PermaNet 2.0.

Bottom Line

As a result of this investigation, in our cost-effectiveness analysis, we are now using an input of 2.11 for the equivalent coverage years of an LLIN provided through AMF’s distributions, relative to nets used in the RCTs that the cost-effectiveness analysis relies on to estimate the impact on child mortality. Nets distributed in DRC receive a 17% durability penalty on this input in our cost-effectiveness analysis based on evidence that nets may decay more quickly in this setting.

This does not represent a median net lifespan estimate (the outcome reported by some literature). Rather, it is a relative input intended to scale along with the expected coverage and protective efficacy of nets used in RCTs.

Our input for equivalent coverage years for a PermaNet 2.0, our reference point net, is 2.27. Although AMF purchases a significant number of PermaNet 2.0s, it also purchases many other brands of nets, some of which we believe may provide somewhat worse protection than PermaNet 2.0. In order to arrive at our estimate of 2.11 equivalent coverage years for AMF nets, we used our estimate for PermaNet 2.0 as a starting point, then adjusted the estimate based on:

• our rough guess of the effectiveness of each net type compared to PermaNet 2.0
• the proportion of each net type as a total of AMF’s net purchases from 2018 through 2020.

Our Process

We searched Google Scholar, VectorWorks' resources page, and PMI's monitoring database for synthesis studies on LLIN lifespan and durability, and later repeated these searches for literature testing the durability of the Vestergaard PermaNet 2.0 and Yorkool LN nets specifically. We also relied heavily on WHO publications regarding LLIN product qualification, field testing, and durability measurement.

We spoke with three outside experts regarding this project, two experts who have led projects to synthesize research on net quality and durability and one funder who has supported research in this area. Finally, we reviewed documentation on net purchases from AMF. AMF reviewed this page prior to publication.

Sources

Document	Source
Ahogni et al. 2020(a)	Source (archive)
Ahogni et al. 2020(b)	Source (archive)
Alaii et al. 2003	Source (archive)
Bhatt et al. 2015	Source (archive)
Binka et al. 1996	Source (archive)
Fettene, Balkew, and Gimblet, 2009	Source (archive)
GiveWell, DRC net durability adjustment, 2021	Source
Gleave et al. 2018	Source (archive)
Habluetzel 1997	Source (archive)
Hakizimana et al. 2014	Source (archive)
Ketoh et al. 2018	Source (archive)
Kilian et al. 2011	Source (archive)
Kilian et al. 2015	Source (archive)
Kilian et al. 2018	Source
Koenker et al. 2014	Source (archive)
List of AMF distributions	Unpublished
List of AMF distributions, public version	Source
Lorenz et al. 2019	Source (archive)
Morgan et al. 2015	Source (archive)
Nevill et al. 1996	Source (archive)
Phillips-Howard et al. 2003	Source (archive)
Pryce, Richardson, and Lengeler 2018	Source (archive)
Rahaivondrafahitra et al. 2017	Source (archive)
Randriamaherijaona, Raharinjatovo, and Boyer 2017	Source (archive)
Sahu et al. 2020	Source (archive)
Strode et al. 2014	Source (archive)
Tan et al. 2016	Source (archive)
The Global Fund, QA Information Notice, DawaPlus 2.0, 2019	Source (archive)
USAID, Durability Monitoring of LLINs in Myanmar, 2019	Source (archive)
USAID, Durability Monitoring of LLINs in Zanzibar, Tanzania, 2019	Source (archive)
USAID, LLIN durability monitoring guidelines, 2019	Source (archive)
Van Roey et al. 2014	Source (archive)
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WHO, Guidelines for monitoring the durability of long-lasting insecticidal mosquito nets under operational conditions, 2011	Source (archive)
WHO, Prequalified Lists: Vector control products	Source (archive)
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WHO, World Malaria Report, 2012	Source (archive)