Our systematic analysis presents mixed findings on ITN ownership and use in children under 5 in 44 countries in Africa. On the one hand, a number of countries have been able to rapidly scale up ITN coverage from essentially zero to above 60% with the most dramatic improvements having occurred in the last two years. On the other hand, only a handful of countries have achieved ITN ownership coverage of 80% or greater. More importantly, countries with large populations at risk of malaria, such as Nigeria, continue to have low coverage, resulting in mean ITN ownership coverage in these 44 African countries of around one third, and ITN use in children under 5 coverage of around one quarter.
Efforts to increase coverage in these countries can be informed by case studies in settings where the scale-up of ITNs has been more successful. The approaches used to scale up ITN coverage in, for example, Eritrea 
, Kenya 
, São Tomé and Principe 
, Tanzania 
, and Zambia 
have been described in depth elsewhere. These strategies include free mass distribution, social marketing, ITN vouchers, and distribution of ITNs as part of routine antenatal care, routine immunization programs, and mass immunization campaigns. Studies to identify determinants of more recent scale-ups identified here, such as Ethiopia, Equatorial Guinea, Liberia, Mali, and Sierra Leone, can further inform strategies in those countries where coverage remains low. Notably, several countries with low levels of coverage of other key interventions have been able to scale up ITN coverage to relatively high levels. Both Niger and Ethiopia, for example, have been able to rapidly increase ITN coverage, yet Ethiopia has skilled birth attendance (SBA) coverage of only 10% while Niger has SBA coverage of less than 20% and DTP3 coverage of about 50% 
In this analysis we have quantified the relationship between DAH targeted at malaria and changes in ITN coverage. While there was substantial variation in the relationship between DAH targeted at malaria and changes in ITN coverage, our results suggest that external financial assistance can be used effectively and that increased funding could help countries with currently low levels of ITN coverage. These associations should be interpreted with caution, however, as we were not able to isolate DAH that is used specifically for ITN distribution. In other words, DAH targeted at malaria may also be used to implement indoor residual spraying (IRS) programs or purchase antimalarial medication. For example, in São Tomé and Principe—one of the identified outliers—most malaria DAH is used for IRS and case management programs rather than ITN procurement and distribution 
. Furthermore, given that even LLINs must be replaced every few years, our results also highlight the need for these funding streams to be sustained or alternative financing to be found if ITN coverage is to be maintained into the future.
An important element of efforts to sustain ITN coverage is a precise assessment of the number of nets required to scale-up coverage and then to maintain coverage (“catch-up” versus “keep-up”). Our method can provide an accurate projection of current and future supply and distribution needs, as it tracks the number of LLINs at different points in the distribution chain, as well as the age of nets in households. This analysis extends substantially on the methods used in previous studies 
that relied on a single source of data to measure the coverage of ITNs in Africa. By combining data from manufacturers, NMCPs, and household surveys, including a number of newly available surveys, we can document in a timely fashion important and substantial increases in ITN coverage in Equatorial Guinea, Liberia, Niger, Mali, Rwanda, São Tomé and Principe, Senegal, and Sierra Leone that were not previously described. We also report on ITN ownership coverage and correct for the effect of seasonality in computing use in children under 5.
While we were able to systematically assess the distribution and coverage of ITNs in African countries, a number of steps could improve the estimates shown here. Our method focuses on national-level coverage estimates. In countries with less than 100% of the population at risk of malaria, the denominator will therefore include both populations at risk and populations not at risk of malaria. As a measure of coverage this implies that ITNs are equally distributed between populations at risk and populations that are not at risk of malaria. As a sensitivity analysis, we have also estimated ITN coverage in populations at risk of malaria assuming that ITNs are exclusively owned and used in populations at risk. These two sets of estimates provide an approximation of the uncertainty of ITN coverage among population at risk of malaria given that it is unlikely that ITNs are preferentially distributed towards populations that are not at risk of malaria. It is important to note that this issue applies only to 12 out of the 44 countries with estimated populations at risk of malaria of less than 100%.
To better measure ITN coverage in populations at risk of malaria, an important direction for future work is to extend this technique to estimate ITN coverage at subnational levels paired with more robust estimates of malaria transmission risk. The estimates of the population at risk of malaria used in this analysis are based on administrative data, are estimated for a single year (2006) and are likely to be uncertain. Extending the model beyond the national level will require future collection of NMCP distribution within each country combined with household surveys that are adequately powered to estimate coverage at, for example, the province or district levels. This will also produce more locally relevant results; the model can also be adapted into software that local program managers could use to monitor and forecast ITN supply and distribution needs. Subnational estimates of ITN coverage should also be complemented by analyses of inequalities in ITN coverage related to socioeconomic indicators such as household wealth, education, and rurality 
We estimated the number ITNs discarded by households from a relatively small number of published studies. Additional net retention studies as well as incorporation of questions regarding past ownership of nets into routine household surveys could reduce this uncertainty. Consistent with WHOPES recommendations, we have also not included LLINs that are older than three years; studies suggest that the decline in the effectiveness of LLINs may be more gradual 
. Improving the quality of NMCP reports would also greatly improve these estimates. Finally, work to examine the relationship between different measures of ITN coverage and health outcomes, such as parasitemia, anemia, malaria-specific mortality, or all-cause mortality, would help to resolve the debate about which measure of coverage—ownership, use, or per capita ratio—is ideal, as well as to continue to build on the available evidence 
regarding the impact of the scale-up in ITN coverage on population health.
Large and rapid increases in ITN coverage have been realized in several countries in Africa, including some of the poorest countries with limited health infrastructure. The expansion of DAH targeted at malaria appears to be a significant contributor to these improvements. This suggests that more DAH could be effective in helping countries achieve ITN coverage goals but also that external financial assistance will need to be sustained if high coverage levels are to be maintained. When increases in ITN coverage have been made, it has often been rapid, emphasizing the importance of timely monitoring. Our method addresses this need by providing an objective and replicable way to monitor the distribution and coverage of ITNs in a continuous fashion. This is critical leading up to September 2010, when the global health community will determine whether the targets set for ITN coverage have been met.