This study described the uptakes of LLINs and the RTS,S/AS01 malaria vaccine in the Lake Victoria region of Kenya in 2024 and examined the factors influencing the uptakes. Although several reports from various areas have addressed LLIN15,27 and malaria vaccine16,17,28 uptake independently, this is the first study to investigate simultaneously both interventions in the same area. We found some common household-level characteristics with four outcomes: net distribution, net usage, vaccine uptake, and vaccine full take. Older average age of the mother, caregiver, or head of the household, proximity to a health center, and higher household wealth were linked to a higher likelihood of receiving or complying with the interventions. However, geographical differences in adoption and compliance could be clearly discerned, and the spatial patterns differed among the measured outcomes. These findings suggest that different sets of actions should be considered to improve the coverage and compliance of these interventions in different areas.
We found that 89.9% of households received new PBO-pyrethroid LLINs around five months after the mass net distribution. This figure is slightly lower compared to the previous report in Uganda15,27, which showed 93.4% of households owned at least one new LLIN after 1–5 months of mass net distribution in 2020–2021. Moreover, Bhatt et al. estimated a median LLIN retention time of 23 months in 40 African countries5. Efforts should be made to get as close to 100% coverage of LLIN distribution as possible, given the possibility of nets being damaged or lost over time. From the regression analysis, we found the households that did not receive the new LLINs were more likely to be headed by younger adults, have fewer children, live farther from a health center, and be less wealthy. Given that nets can be an asset, the reasons for not receiving the new nets are likely to be different from the reasons for not using them or not having their children vaccinated. More likely, people wanted new nets but were omitted from the mass distribution. During the net distribution process, household heads were instructed to collect their new nets from designated locations such as health facilities and primary schools. Households that did not receive new nets either failed to visit the collection point or were not included in the distribution registry. As these people who did not get nets could be socially isolated, it is important to incorporate these people into public policy targets. In addition, the mass net distribution campaign in 2023 was the first time an electronic registration system was used to identify eligible households in the study area. Anecdotally some CHPs participating in both our study and the mass net distribution mentioned that there was some difficulty in utilizing the new technology, possibly resulting in the omission of some households.
Compared to net distribution, net usage showed less geographical clustering, suggesting that measures need to be directed towards a wider area population in order to increase net usage. A good approach to reaching a wider population is spreading the knowledge about malaria prevention. Kanyagarara et al. reported that knowledge of LLIN was associated with a 30–40% increased OR of net use in Zimbabwe and Zambia29. Additionally, previous studies in SSA reported that household size was strongly associated with inequality in the use of LLIN27,29,30, which is consistent with our results. Moreover, Tamari et al. reported sharing LLIN with two or more individuals may compromise its protective effect in areas close to our study site31. It is important to recognize that in large households, every member may not have equal access to LLINs, and a single net is often shared by several members. Another issue we observed in the field was the lack of awareness regarding the expiry date of the LLINs. Although this was not part of a structured survey, we identified several people who were unaware that the nets are treated with insecticide and will lose their effectiveness after a few years. As a result, people tend to keep using old nets until they are physically damaged, which may lead to lower acquisition and usage of the new nets32.
Regarding malaria vaccine coverage, we found that only the dose 1 uptake met the WHO coverage target of 80% across all health centers in the study area. After dose 2, coverage rates dropped dramatically, a trend commonly reported in other studies of malaria vaccines14,17,28 and other multi-dose childhood vaccines33,34. Since the regimen of the nelwy launched R21/Matrix-M vaccine is similar to that of the RTS,S vaccine, factors that lower the full uptake of the latter are likely to apply to the former. From the regression analysis, we found that households that did not complete the full RTS,S regimen were typically headed by younger adults, had more children, lived farther from a health center, and were less wealthy. One possible explanation for these findings is that households with these characteristics may not have the time and resources to ensure that all children are fully vaccinated. These populations should be prioritized to increase full-dose coverage of malaria vaccines. Although many efforts have been made to increase vaccination completion under the current immunization schedule, there have also been discussions about the possibility of changing the schedule itself. Alongside the development of a new vaccine with a shorter regimen35, there is an ongoing study evaluating modification of the regimen and dosage of RTS,S vaccines without compromising their efficacy36. This should be focused on which regimen has a chance to increase the completion rate in each area setting based on the local context. We believe this could be the ultimate form of tailor-made malaria control strategy.
Households with eligible children that did not take any dose of malaria vaccines differ from those with children who were not fully vaccinated based on the spatial distribution (Fig. 3) and the regression analysis (Table 1). Especially, proximity to the nearest health center was not associated with vaccine uptake. This suggests that vaccine hesitancy may be more prominent in some areas and/or populations. Simbeye et al. reported that in Malawi, some did not take any dose of malaria vaccine because of religious beliefs34. In our study, some CHPs reported that certain religious leaders discouraged their followers from accessing publicly available health services, including malaria vaccination, as a reason for the abundance of malaria-unvaccinated households in their areas. In addition, it is known that trust in vaccines–not just malaria vaccines–has a profound effect on vaccine hesitancy in SSA countries37,38. Unfried et al. showed that individuals’ trust in the government and society are key predictors of hesitancy towards polio, human papillomavirus, and COVID-19 vaccines in six countries (Ghana, Kenya, Nigeria, South Africa, Tanzania, and Uganda). Incorporating factors related to vaccine trust would provide a more holistic understanding of the barriers of malaria vaccine in future studies.
One of the strengths of our analysis is the incorporation of spatial aspects. Although there is growing awareness of spatial dependencies driven by proximity or shared social and environmental factors39, there are still limited studies that explicitly account for spatial aspects in malaria research40. While our regression analysis reaffirmed the known factors influencing LLIN and vaccine uptake, it is noteworthy that we found similar associations even after considering spatial correlation.
There are several limitations in this study. First, as we utilized baseline survey data from a cluster randomized trial that was not originally designed for this study, we did not conduct a sample size calculation for the analysis. As a result, we may not have achieved precise estimates, particularly in the regression analysis. Nevertheless, we categorized each explanatory variable into three strata, which may suggest dose-response trends. Second, although CHPs were instructed to review the mother-child handbook to obtain malaria vaccination history, verbal reports were sometimes used if the mother had lost her handbook or if time constraints limited the survey. This introduces the possibility of recall bias, particularly regarding vaccination history. Additionally, the analysis may include individuals who moved into the study area from regions where the pilot vaccination program was not implemented.
In conclusion, as the characteristics of households who did not receive or comply with net distribution, net use, vaccination, and full vaccination overlap but differ slightly within the same area, tailored activities should be implemented to enhance the overall uptake of different interventions.