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Long-Lasting Insecticide Treated Net (LLIN)

Insecticide-treated bed nets (ITNs) are a form of personal protection from mosquitoes during sleep that have been shown to reduce malaria illness, severe disease, and death due to malaria in endemic regions. Long-lasting insecticide-treated nets (LLINs) maintain effective levels of insecticide to repel mosquitoes for at least 3 years, even after repeated washing.

Unit of interventionper LLIN

Effective lifespan of intervention3 - 5 years

Target populationhouseholds at risk for malaria

For more information about how PSI uses LLINs to improve health and save lives, visit our website at:
http://www.psi.org/health-area/malaria/

Model Overview

PSI’s LLIN impact model is based on the Lives Saved Tool (LiST). LiST is used to estimate the number of deaths averted by complete coverage of ITNs for prevention of malaria in select countries over a three year period, representing the projected impact of LLINs. The indicator used by LiST is household ownership of ITNs, not use of ITNs. This number of deaths averted at the population level is translated to deaths averted per LLIN, using parameters such as the percent of the population exposed to malaria, baseline coverage of LLINs, effectiveness of LLIN ownership on under-five mortality, and the average number of LLINs in households owning LLINs. Once we have deaths averted per LLIN, we apply data from the 2010 Global Burden of Disease study to estimate the corresponding number of DALYs averted.

Model Outputs (impact metrics)

Estimates of DALYs averted, deaths averted, CYPs provided, and unintended pregnancies averted represent the projected health impact of the intervention. It is “projected” because it has not been directly measured.

Examples based distribution of LLIN in Myanmar in 2015 Statement of modeled results, examples:

If 10,000 LLINs were distributed in Myanmar in 2015, they would avert an estimated 16 deaths and 805 DALYs over the course of their effective life span.

For more details about how PSI models the impact of LLINs, see below.

Model Details

Step 1: Running a projection in the Lives Saved Tool (LiST)LiST is a multi-cause mortality model developed by Johns Hopkins Bloomberg School of Public Health that estimates the number of deaths averted (or lives saved) through the scale up of maternal and child health interventions.

PSI begins by running a projection in LiST for select countries. In this projection, household ownership of ITNs is increased from the current, country-specific baseline to 100%. This coverage is increased to 100% for a three year time period in order to represent the impact of LLINs over their effective lifespan. LiST then projects the number of deaths averted among children under five by this increased level of coverage.

Step 1 Output:
Number of additional deaths averted (or lives saved) among children under five if coverage of LLINs increased from baseline to 100%

Step 2: Estimating deaths averted per LLIN among children under five (deaths averted coefficient)

PSI uses the step 1 output (deaths averted at 100% coverage of LLINs over a three year period) to estimate the number of deaths averted by a single LLIN. To do this, we divide the number of deaths averted at 100% coverage by the number of LLINs needed to reach 100% coverage of households at risk for malaria.

PSI estimates the number of LLINs needed to reach 100% coverage using a number of parameters, including the percent of the population exposed to malaria, baseline coverage of LLINs, effectiveness of LLIN ownership on under-five mortality, and the average number of LLINs per household owning LLINs. We also account for wastage of LLINs in the supply chain, assumed to be 10%.

Step 2 Output:
Under five deaths averted coefficient for LLINs

Step 3: Estimating DALYs averted per LLIN among children under five (DALYs averted coefficient)A DALY (or disability adjusted life year) includes two components: years of life lost due to premature death (YLL) and years lived with disability (YLD). DALYs averted are in turn comprised of YLLs averted and YLDs averted or, put simply: death and disability that is prevented by PSI interventions.

To estimate YLLs averted per LLIN among children under five, PSI first estimates the number of years of life lost per malaria death among children under five in select countries. This is equal to the life expectancy at the average age of death from malaria. Age specific life expectancy is taken from the 2010 Global Burden of Disease study (GBD). The number of years of life lost per malaria death is then multiplied by the number of deaths averted per LLIN among children under five (under five deaths averted coefficient), calculated in step 2 above for a selected country. This gives us the YLLs averted per LLIN.

To estimate YLDs averted per LLIN among children under five, we use a YLD/YLL ratio, based on GBD 2010. This ratio represents the relative number of years lived with disability for every year lost due to death from malaria. We apply this ratio to the number of YLLs averted per LLIN to estimate the number of YLDs averted per LLIN among children under five.

Finally, YLLs averted and YLDs averted are added together to estimate the number of DALYs averted per LLIN among children under five.

Step 3 Output:
Under five DALYs averted coefficient

Step 4: Extrapolate deaths and DALYs averted among children under five to all agesLLINs impact individuals of all ages. In order to estimate impact at the population level, we have to extrapolate deaths and DALYs averted among children under five to deaths and DALYs averted among all ages. This is done by using two new ratios, both of which are calculated using GBD 2010:

Ratio 1: Number of deaths among children under five / deaths among all ages
Ratio 2: Number of DALYs among children under five / DALYs among all ages

Each ratio is applied to its respective impact coefficient (deaths or DALYs averted among children under five per LLIN) to estimate the number of deaths and DALYs averted among all ages.

Step 4 Outputs:
Deaths averted coefficient (all ages)
DALYs averted coefficient (all ages)