Insecticide-treated nets (ITNs) are effective tools for malaria prevention and can significantly reduce severe disease and mortality due to malaria, especially among children under five in endemic areas [1]. However, ITN ownership and use remain low and inequitable among different socio-economic groups in sub-Saharan Africa [2]. With the significant increase in funding in the recent decade, many countries across sub-Saharan Africa are rapidly increasing ITN ownership coverage, that is the percentage of households which own at least one ITN, through several strategies including, social marketing [3, 4], free distribution to target groups (through antenatal care (ANC) or immunization campaigns) [5–9], and more recently, free universal population-based distribution campaigns targeting the entire population at risk [3, 5, 10].

Free distribution campaigns aim at the Roll back Malaria (RBM) goal of universal coverage as opposed to the previous strategies that focused on targeting only pregnant women and children under five. The aim is to achieve the newly agreed-upon Roll Back Malaria (RBM) Partnership target of one ITN for every two people by 2015 [RBM 2008]. Mass ITN distribution campaigns targeting all persons at risk for malaria, particularly in high transmission settings, have the advantage of rapidly achieving high community-level coverage which benefits everyone in the community and not just those who own and sleep under nets [10]. This strategy also has the potential to achieve equity in mosquito net ownership and use, shown by a number of studies in different settings [3, 5]; however, the level of achievement depends largely on context specific settings and the effectiveness of the distribution strategy. It is, therefore, important to assess equity in mosquito net ownership and use after each mass distribution in a new setting.

Nigeria is currently engaging in free mass distributions of long-lasting insecticidal nets (LLINs), a type of ITN that is factory-treated and designed to maintain efficacy against mosquito vectors for at least 3 years. The national malaria control strategy plan calls for the distribution of 63 million new LLINs by the end of 2010 and for at least 80% of these nets to be put into use [11].

The first state to implement this new approach was Kano, where several partners, including the U.S. Agency for International Development (USAID), the World Bank, Malaria Consortium, and Support to Nigeria Malaria Programme (SuNMaP), joined forces for implementation. This campaign, which was conducted in two waves in May and July 2009, distributed more than 4 million mosquito nets in State (Malaria Consortium). In Wave 1 of the campaign, which was conducted in May 2009, households with less than nine members received one voucher for two LLINs and those with more members received two vouchers. As a mainly Muslim state, polygamy is common in Kano; therefore, modifications were made in Wave 2 (July 2009) so that each wife and her direct dependents received one voucher for two LLINs.

The urgent need for data to inform policy regarding the scaling up of the campaign strategy drove the decision to carry out a post-campaign evaluation of the first two campaigns implemented in Kano. Using data from the post-campaign survey [12] the authors investigated the effect of the free mass distribution campaign in achieving equity in mosquito net ownership and use.

Using logistic regression and equity analysis, the impact of free universal distribution of ITNs on the equity in ownership and use in Kano State was assessed. The results show that following the distribution campaigns the disparity in mosquito net ownership among households from different socio-economic groups was reduced. Comparably, mosquito net use was similar among the different socio-economic groups. No difference was observed between rural and urban populations for mosquito net ownership or use.

The two free distribution campaigns have helped to substantially increase mosquito net ownership coverage in Kano state. Before the campaigns, approximately 10% of households in Kano state owned at least one mosquito net; this low coverage is similar to national-level coverage reported in Nigeria (17%) [15]. After the campaign, coverage increased substantially to 70% in Kano state. These findings are consistent with other free mass distribution campaigns that have been carried out in sub-Saharan Africa [16–20], demonstrating that free mass distribution of ITNs can be used as an effective strategy to quickly scale-up ITN coverage in areas with low coverage. With the substantial increase in household ownership, there was concern as to whether or not the distribution campaign was also beneficial to disadvantaged subpopulations from the lowest socio-economic group. Further analyses demonstrate that coverage is equally as high among these groups.

Equity in household ITN coverage improved after the mass distribution campaigns. Prior to the campaigns, ITN ownership was greater among wealthier households as demonstrated by a positive concentration index of 0.21. After the two campaign waves, the concentration index was found to be close to zero with no statistically significant difference found between wealth quintiles in household ownership of at least one ITN. The fourth (second least poor) quintile did show higher odds for ITN ownership; however, this was not statistically significant. The findings indicate that the campaign was able to reach all households equitably and reduce the observed (before campaign) inequity in ITN ownership, suggesting a relatively fair household listing and distribution process. These results corroborate evidence from other free mass distribution campaigns that provide ITNs to the entire population at risk for malaria; all show high and equitable ITN ownership after the campaign [3, 5, 10, 16–20].

Free mass distribution campaigns appear to be a more effective strategy to rapidly achieve high and equitable household ITN ownership coverage than other bed net distribution mechanisms, such as socially-marketed ITNs and free targeted distribution campaigns for children under five and pregnant women [10]. Strategies that involve even a nominal financial contribution from individuals are likely to benefit only those who can afford or are willing to pay for the commodity. Effective malaria control efforts using ITNs strive for high-level coverage in order to impact malaria morbidity and mortality. Therefore, free distribution seems to be an effective strategy to achieve equitable coverage at the community level that will be beneficial to everyone. High levels of ITN coverage reduce the prevalence, density and infectiousness of malaria parasites in the human population [10, 21]. Other distribution strategies are less likely to achieve such high coverage, missing poorer households or those that do not have children under five or pregnant women.

ITN use was found to be relatively high after the survey, with 53.3% of individuals reporting using an ITN the night before the survey visit. However, about half of the individuals did not use ITN; this could be because of the hot weather, though absence of mosquitoes [22] could also be a factor. In northern Nigeria the annual average temperature is about 26.4 degrees Celsius; however, the average temperature was slightly higher at 27.3 degrees Celsius when the survey took place. This high temperature could cause some discomfort, especially when sleeping indoors, and some people may choose either not to use the net or to sleep outside where they are less likely to use a mosquito net. Since the hot weather is reported as a deterrent for mosquito net use in October when the temperatures are around the annual average, one should expect higher non-use in March through April when the average temperature is above 30 degrees Celsius. October corresponds to the month after the rainy season, suggesting that mosquito abundance may be low, especially if the residual mosquito breeding sites from rain water have already dried out. The nuisance of mosquitoes may have reduced substantially, resulting in reduced need to use a mosquito net. Nonetheless, the findings reveal no significant association between socio-economic status and mosquito net use after the campaign. While the lower two quintiles did show a reduced odds of ITN use, indicating greater odds of use among the wealthier quintiles, the differences were not statistically significant.

While mass distribution campaigns are able to rapidly achieve high and equitable mosquito net ownership, they are unable to provide continuous coverage for a population at risk for malaria as they only occur every few years. To provide continuous coverage, complimentary mosquito net distribution strategies need to be in place to reach people that are missed by campaigns. Such strategies could cover newborns and pregnant women between campaigns [5, 21, 23] as well as immigrants in areas with high population mobility. Targeted bed net distribution through antenatal care or through mass drug administration or vaccination campaigns can provide effective coverage in between campaigns to ensure that newborns and pregnant women are covered [4, 6–9, 16, 24, 25].

It is critical that increased ITN ownership and use be sustained to keep the disease burden low and potentially move towards eradication and elimination. Therefore, having complimentary bed net delivery strategies is necessary for replacing nets that are worn or damaged during the time in between mass distribution campaigns. These strategies should focus primarily on targeting poorer households, as poorer households are less likely to be able to or willing to replace worn or damaged bed nets or retreat bed nets compared to wealthier households [26]. Furthermore, bed nets could be more likely to get damaged more quickly in poorer and rural households than in wealthier or urban households due to the living conditions. Wealthier households may also be less prone to selling or trading their bed nets for immediate household needs [27]. For all of these reasons, additional ITN delivery strategies are necessary to complement mass distribution campaigns to ensure continuous and equitable coverage.

Further study to assess the survival time of the mosquito net and the factors associated with will help define a cost effective strategy for replacement in order to sustain achievements of free distribution campaigns. It will also be critical that the level of funding in malaria control be maintained or increased to sustain the free distribution strategy.