ITN Quantification Site

About

What is the ITN Quantification Site?

The ITN quantification site presents the number of ITNs required to achieve and maintain targeted levels of ITN access with different combinations of distribution channels and estimates of ITN longevity. The site provides two things:

1. An illustrative comparison of the numbers of ITNs required for different distribution scenarios by country in sub-Saharan Africa where malaria is endemic.
2. A user-friendly way to look up recommended ITN population quantifiers for school-based and community-based continuous distribution. These quantifiers can be applied nationally or sub-nationally.

What the site is not

The ITN quantification site does not provide:

1. A precise estimate of the number of ITNs needed under different distribution scenarios. Estimates of ITN need are presented at the national level using population estimates from the World Bank. Results do not consider different subnational tailoring approaches to ITN distribution, including areas where ITNs may not be distributed at all.
2. Guidance on which distribution strategy or distribution channels a country should choose. This decision will be informed in part by the number of ITNs needed to achieve and sustain a target level of ITN coverage but should also consider the appropriateness and feasibility of a given channel, and other country contextual information, including the prioritized interventions and channels in the National Malaria Strategic Plan and/or the integrated vector management policy. Guidance on channel selection for ITN continuous distribution and operationalising distribution is available in the ITN Continuous Distribution Toolkit.

The main assumptions and limitations for the content of this site are presented under additional information.

How do I use the site?

Five different ITN outputs are available on this site:

• Need by distribution strategy
• Access over time
• Need for different lifespans
• Cost benefit of distribution strategies
• Quantifiers for continuous distribution

You will be able to explore how these outputs change with different distribution strategies, target access levels, and estimates in ITN lifespan. Your focus country can be changed using the drop-down options at the top of the sidebar.

The ITN distribution strategies that are presented on this site are:

• Mass campaign every 2 years
• Mass campaign every 3 years
• Mass campaign every 3 years with continuous distribution (CD) in years without a mass campaign
• No mass campaign, continuous distribution (CD) only

These are common strategies, or alternative strategies that may be considered.

All strategies assume that ITNs are also distributed to pregnant women at antenatal clinics (ANC channel) and to infants at child health or vaccination visits (EPI channel) using a “population multiplied by 6%” quantifier.

ITNs Needed by Distribution Strategy

The charts below show at national level the total number of ITNs needed to achieve a target level of ITN coverage under different distribution strategies.

The target level of ITN access (70%, 80% or 90%) and the time span over which ITN numbers are calculated (3 years or 10 years) can be changed using the drop-down options above the charts. The ITN lifespan is the modelled value from Bertozzi-Villa (2021) for the country that is selected.

Results are presented first for strategies that include continuous distribution, either alone or in combination with mass campaigns every 3 years, then for mass campaigns alone conducted every 3 years and every 2 years. The charts present the total number of ITNs required for the strategy over the period.

Two results are shown for each mass campaign alone strategy.

The top bar is the number of ITNs required to meet the coverage target using a mass campaign quantification approach of “population/1.8”, i.e., using the currently recommended approach. Note that although this number of ITNs may meet the access target, the target will not be maintained over time.

The bottom bar shows the number of ITNs that would be required if the mass campaign distributed enough nets to achieve and maintain the access target, using a tailored quantifier rather than “population/1.8”.

ITN Access Over Time by Distribution Strategy

This chart shows ITN access over time for a given target level of ITN access under different distribution strategies. It shows how ITN need for a given strategy and coverage target presented in the first visualization translates into population ITN access over time.

The target level of ITN access (70%, 80% or 90%) and the distribution strategy can be changed using the drop-down options above the chart. The ITN lifespan is the modelled value from Bertozzi-Villa (2021) for the selected country.

Four distribution strategies can be reviewed:

• Mass campaign every 2 years
• Mass campaign every 3 years
• Mass campaign every 3 years with continuous distribution (CD) in years without a mass campaign
• No mass campaign, continuous distribution (CD) only

For strategies that include mass campaigns, this chart uses “population/1.8” as the quantification approach.

For mass campaigns every 2 years and every 3 years, the ITN access target can be achieved immediately following the campaign, but access is not maintained over time. Strategies that include continuous distribution can maintain the access target.

ITNs Needed for Different ITN Lifespans

This chart shows the total number of ITNs needed over three years at the national level to achieve a target level of ITN access under two strategies that include continuous distribution if different estimates of ITN lifespan are used. For example, data from durability monitoring sites may be available to estimate a national ITN lifespan.

The estimated ITN lifespan (from 1 year to 3.5 years) can be changed using the options above the charts.

Results are shown for two strategies:

• No mass campaign, continuous distribution (CD) only
• Mass campaign every 3 years with continuous distribution (CD) in years without a mass campaign

Mass campaign strategies with no continuous distribution are not presented as quantification for mass campaigns is based on population estimates, not net lifespan.

For each strategy, different bars present the ITN needs for access targets of 70%, 80% and 90%.

Cost Benefit of Different Distribution Strategies

This chart shows person-years of protection, expressed as person-years of ITN access, against total ITNs, for four ITN distribution strategies and different coverage targets.

The results shown can be used to assess the cost benefit of different scenarios in terms of the additional population protection that results with a given increase in total ITNs distributed.

Total nets shown on the y-axis is the total number of nets required over X years for a given distribution strategy and for a given coverage target.

Person-years of ITN access shown on the x-axis is the sum of the years of protection that the strategy will deliver for an estimate of the national population assuming a given access target.

Results are shown for four distribution strategies:

• Mass campaign every 2 years
• Mass campaign every 3 years
• Mass campaign every 3 years with continuous distribution (CD) in years without a mass campaign
• No mass campaign, continuous distribution (CD) only

Estimated ITN lifespan is the modelled value from Bertozzi-Villa (2021).

For strategies that include mass campaigns, this chart uses “population/1.8” as the quantification approach for campaigns.

Population Quantifiers for Continuous Distribution

This table shows the population quantifiers that are recommended for continuous distribution with different ITN lifespans and target levels of ITN access.

Quantifiers are presented for the two strategies that include continuous distribution (alone or in combination with mass campaigns) and for estimated ITN lifespans from 1 year to 3.5 years.

The quantifiers can be applied to populations nationally or subnationally (e.g., district or region). How they are used depends on the country’s policy and strategy for continuous distribution.

The blue column in the table highlights the modelled ITN lifespan from Bertozzi-Villa (2021).

These quantifiers are for the non-routine continuous distribution channels only, i.e., school-based distribution and community-based distribution. Both strategies assume that ITNs are also distributed to pregnant women at antenatal clinics (ANC channel) and to infants at child health or vaccination visits (EPI channel) using a “population multiplied by 6%” quantifier separate to what is shown here.

The results in this table have two linked uses. First, they show how to quantify ITN needs annually for continuous distribution. For example, a 10% quantifier (for a given strategy, target and ITN lifespan) means that a country would need to quantify ITN need as “population multiplied by 10%” to achieve the target ITN access.

Second, the quantifiers can be used to inform more detailed distribution strategy design. For example, if the same country is planning to implement school-based distribution, then planners need to ensure that the total number of children in the classes they select makes up at least 10% of the total population for the geographic area of interest.

Additional Information

Data Sources

ITN quantifications, ITN access estimates, continuous distribution quantifiers and all underlying data are taken from: Koenker H, Yukich J, Erskine M, Opoku R, Sternberg E, Kilian A. How many mosquito nets are needed to maintain universal coverage: an update. Malaria Journal. 2023;22:200.

Modeled ITN lifespans (called “ITN retention times” in the publication) used in Koenker (2023) were originally presented in: Bertozzi-Villa A, Bever CA, Koenker H, Weiss DJ, Vargas-Ruiz C, Nandi AK, et al. Maps and metrics of insecticide-treated net access, use, and nets-per-capita in Africa from 2000-2020. Nature Communications. 2021;12:3589.

Population data are national estimates taken from the World Bank Open Data Initiative. The indicator used “Population, total”, with code SP.POP.TOTL, available at: https://data.worldbank.org/indicator/SP.POP.TOTL?view=chart. Further citations are available from this webpage as sources vary by country.

Main Assumptions and Limitations

• All strategies assume that ITNs are also distributed to pregnant women at antenatal clinics (ANC channel) and to infants at child health or vaccination visits (EPI channel) using a “population multiplied by 6%” quantifier. This assumes a relatively robust health system with high ANC and vaccination attendance and reasonable efficiency at reaching these populations with ITNs. In many contexts, improvements to routine distribution system would be needed to meet this assumption.
• All strategies assume a mass campaign occurs in “Y1” as presented in the visualization for ITN Access Over Time. This includes the scenario “No mass campaign, continuous distribution (CD) only”, for which there is a mass campaign in Y1 and then continuous distribution (CD) only in subsequent years.
• Durability monitoring studies sometimes find significantly longer median survival of ITNs compared to the modelled retention time estimates. Note that we’ve included the option to modify ITN lifespan in some of the outputs.
• Longevity estimates from both durability monitoring studies and model output are almost entirely based on pyrethroid-only ITNs. As data are collected on new types of ITNs, estimates of longevity may need to be re-examined.
• In the quantification model, the relationship between nets-per-capita and ITN access is assumed to be consistent regardless of ITN distribution strategy, but it is likely that it would be influenced by oversaturation of ITNs in certain types of households.

Why the change from NetCalc?

• This site replaces the NetCALC and NetCALC Lite tools that were previously used to quantify ITN needs. It can be referenced when planning to implement continuous distribution as a new distribution channel, or to refine ongoing continuous distribution activities.
• Recent work (Koenker, 2023) has shown that NetCALC overestimates ITN access for a given number of nets-per-capita. This overestimation is more pronounced at higher levels of ITN access and for countries with smaller average household size. Also, since NetCALC was developed in 2009, we now have country-specific estimates of ITN lifespans (Bertozzi-Villa, 2021) which can be used to better quantify ITN needs for a given country.