1. Introduction

Soil-transmitted helminthiasis (STH) remains a significant health concern, particularly in low and middle-income countries (LMICs) [1]. Common STH include roundworm (Ascaris lumbricoides), whipworm (Trichuris trichiura), and hookworms (Necator americanus and Ancylostoma duodenale). They are most prevalent in sub-Saharan Africa, South Asia, and parts of Latin America [1,2]. These parasites mainly infect humans through penetration of the skin by infected larvae or ingestion of eggs present in contaminated soil, water, or food [3].

Globally, over 1.5 billion people are infected with these parasites, with women of reproductive age (WRA) and school-age children (SAC) being particularly vulnerable to the morbidity associated with STH, such as anemia, malnutrition, impaired growth, and learning [2]. While these infections rarely cause death, prolonged infection can lead to serious issues like iron deficiency (anemia), malnutrition, stunted growth, and even impaired cognitive development in children, which can result in lasting educational and economic disadvantages [4,5].

For over a decade, mass drug administration (MDA), using a single dose of albendazole or mebendazole, has been the primary strategy for control of STH. These programs, often carried out in schools, have significantly reduced infection rates [6]. However, reinfection remains a common problem, especially in places without access to clean water, improved sanitation, and hygiene education [7].

This ongoing challenge has sparked global interest in more comprehensive approaches. New strategies for STH control and elimination aim to combine MDA with water, sanitation, and hygiene (WASH) initiatives, along with health education and social behavior change (SBC). Furthermore, in areas where various parasites are prevalent, the use of combined therapies, such as administering ivermectin and albendazole together, shows promise for more comprehensive and successful parasite control [8].

Furthermore, recent evidence from Phase 2/3 clinical trials has demonstrated that the co-formulation of albendazole and ivermectin in a fixed-dose combination (FDC) significantly improves treatment efficacy against Trichuris trichiura compared to the standard single-dose albendazole monotherapy. However, we still need to learn more about their economic benefits through further research.

Although the need to improve the integration and sustainability of STH control and elimination efforts is well recognized, there is notably less evidence from economic evaluations of these interventions. Many studies have looked at the epidemiological impact of MDA, WASH, and education strategies, but few have applied cost-effectiveness models to compare these impacts with costs [9–11].

The few existing cost-effectiveness studies further differ in their methods, the range of interventions and delivery platforms, outcome measures, and settings of implementation, which makes it hard to compare them. A systematic mapping of the existing evidence is required to identify what has been modeled, how it has been modeled, and the gaps remaining.

This scoping review aimed to gather information on the various STH interventions, analytical methods, and assumptions used in STH cost-effectiveness modeling. This will help inform future STH modeling studies and strengthen the economic understanding of STH elimination programs.

We specifically aimed to (a) identify and describe the modeling studies that evaluate the cost-effectiveness of STH control and elimination programs, (b) detail the economic evaluation methods used across these studies, (c) summarize the types of interventions assessed and the approach of delivery, including MDA, primary health care (PHC), WASH programs, health education, and integrated programs, and (d) compare the reported economic outcomes and identify the specific factors that influence cost-effectiveness.

2. Materials and methods

A review protocol for this study was published in the Open Science Framework on September 8, 2025, with updates on September 28, 2025, and can be accessed at https://osf.io/cz5xj. The writing of the manuscript of this scoping review followed the Preferred Reporting Items for Systematic reviews and Meta-Analysis extension for Scoping Reviews (PRISMA-ScR) guidelines. The PRISMA-ScR checklist can be found in the S1 File (PRISMA-ScR Checklist). An initial search strategy and selection criteria were developed to guide the development of this scoping review. We used the five-step scoping review process that Arksey & O’Malley [12] proposed, which included research question identification, study identification, relevant study selection, data extraction, and result presentation.

2.3. Eligibility, screening, and selection criteria

Studies that performed economic analyses, specifically cost-effectiveness models or combined cost and cost-effectiveness analyses, on STH were included. This includes intestinal worms, Strongyloidiasis, and other STH infections listed in the search query. Eligible studies were published in English, did not include protocols or reviews, and examined preventive chemotherapy interventions such as albendazole, mebendazole, levamisole, or ivermectin, or other auxiliary interventions like WASH, PHC, health education, SBC, or integrated programs. We placed no restrictions on publication year or geographical location.

All records were imported into Mendeley Reference Manager, which served as the automated tool for identifying and removing duplicate records. Screening took place in two stages. First, we reviewed titles and abstracts to identify studies focused on cost, cost-effectiveness, economic modeling, or related economic evaluations. We excluded records that did not meet the inclusion criteria. Second, four reviewers independently assessed the full texts to confirm each study’s relevance to the specified diseases and interventions. We resolved discrepancies through discussion and sought periodic input from senior reviewers. Final inclusion followed the PRISMA-ScR guidelines [13]. Table 1 shows the rationale and criteria for eligibility of including studies in this review.

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Table 1. Eligibility criteria for publications in the review and the rationales for selecting these criteria.

https://doi.org/10.1371/journal.pntd.0014317.t001

2.3.1. Quality assessment of the extracted records.

Although established critical appraisal tools for economic evaluations exist, such as the Drummond checklist and Joanna Briggs Institute (JBI), in keeping with the objectives of this review, we did not apply these formal tools. Instead, during the full-text review and data extraction process, we took into account descriptive indicators of quality, such as records with accessible cost-effectiveness metrics (e.g., Incremental Cost-Effectiveness Ratios (ICERs), Disability-Adjusted Life Years (DALYs) averted, unambiguous economic evaluation techniques, and relevance to the targeted helminths and the interventions evaluated.

3. Results

3.1. Description of study selection

Drawing on the Arksey and O’Malley framework, we synthesized findings from twenty-two studies, mapping their study characteristics, methods, and outcomes, while also identifying critical gaps in the evidence base. A PRISMA flow diagram (Fig 1) summarizes the stages of the study selection process, from identification through screening and final inclusion. The included studies represented a broad geographical distribution, with the majority of the studies conducted in sub-Saharan Africa, followed by East and Southeast Asia, and a smaller number from Latin America. Two studies were modeling-based and not tied to specific field sites.

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Fig 1. PRISMA flow diagram showing the identification, screening, and inclusion processes.

https://doi.org/10.1371/journal.pntd.0014317.g001

3.2. Target populations, geographic scope, and intervention modalities

Table 2 outlines the details extracted from each study, which includes: the author, publication year, geographic location, primary research focus, target population, type of intervention assessed, and key economic outcomes reported.

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Table 2. Summary characteristics of studies included in the scoping review.

https://doi.org/10.1371/journal.pntd.0014317.t002

3.2.1. Geographical distribution.

Across the 22 studies, sub-Saharan Africa accounted for the largest share of evidence (59%, n = 13), with particularly high representation from Kenya (n = 3) and Côte d’Ivoire (n = 3), followed by Uganda (n = 2), Nigeria (n = 2), Madagascar (n = 1), Niger (n = 1), and Ghana (n = 1). Southeast/East Asia contributed 18% (n = 4), including China, Vietnam, the Philippines, and Lao PDR. Latin America was represented by a single study from Brazil (5%). Fig 2 presents a geographical map showing the countries represented in the included studies, while noting that two studies were excluded from the figure because they were modeling-based and not tied to a specific country.

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Fig 2. Geographic distribution of included studies.

Countries are shaded according to the number of studies conducted in each location. The maps were generated using QGIS v3.42 (www.qgis.org; vector map: Natural Earth: www.naturalearthdata.com/about/terms-of-use). The basemap used is the Natural Earth (public domain).

https://doi.org/10.1371/journal.pntd.0014317.g002

3.2.2. Target populations.

Most programs focused on school-aged children (41%, n = 9) (Fig 3), reflecting WHO guidelines. A larger proportion (59%, n = 13) expanded to entire communities, including adults, WRA, and in some cases, Pre-SAC, with evidence that this expansion improves cost-effectiveness in moderate to high prevalence settings [7,14,15].

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Fig 3. Distribution of target populations among included studies.

https://doi.org/10.1371/journal.pntd.0014317.g003

3.2.3. Types of intervention.

The majority of studies (68%, n = 15) examined MDA, either school-based, community-wide, or integrated into neglected tropical disease (NTD) programs. School-based MDA programs were delivered at low cost, ranging from $0.03 to $0.76 per child treated, and were often integrated with other NTD control activities to improve efficiency (Brooker et al., 2008; De Neve et al., 2018; Leslie et al., 2011). Evidence from Uganda and other settings demonstrated that economies of scale (the cost advantage that arises with increased output, where the average cost per unit decreases as the number of people treated increases [16]) significantly reduced per-child costs as coverage expanded [17,18].

Community-wide MDA interventions were frequently more cost-effective per DALY averted than school-based approaches, particularly in high-prevalence settings with substantial adult infection burdens. Reported ICERs for these programs ranged from $28.55 to $198 per DALY averted [19,14]. Expanding treatment beyond SAC increased the overall impact on transmission and improved cost-effectiveness.

Integrated or multi-disease delivery models also showed strong economic performance. In Nigeria, bundling ivermectin, albendazole, and praziquantel into a single delivery platform reduced per-person delivery costs by 41% [20]. Favorable DALY and benefit-cost ratios were also achieved in Lao PDR and Madagascar [21,22]. One study modeled the combination of a hypothetical hookworm vaccine with MDA in Brazil, aiming to reduce reinfection rates and extend deworming benefits [23].

4. Discussion

This scoping review revealed that community-wide and integrated MDA approaches tend to be more cost-effective than school-based delivery in high-prevalence settings, particularly when combined with other NTD programs and scaled to larger populations.

The ICER reported by the studies ranged from US$14 to US$198 per DALY averted. The variation was largely due to differences in coverage levels, integration, and baseline prevalence. That is, the cost-effectiveness of STH interventions is highly context-specific, influenced by delivery strategy, population coverage, and program integration. In high-prevalence settings, community-wide MDA was more impactful than school-based delivery because adult treatment interrupts transmission, but reinfection limited overall effects [14,15]. However, the operational feasibility of such approaches relies on the ability to reach geographically reduced infected adult populations and health systems’ willingness to incur higher upfront costs. Integrated NTD campaigns consistently improved cost-effectiveness by sharing delivery platforms and reducing per-person costs [22,20].

Further, we found uneven amounts of data on cost-effectiveness from endemic regions. Most studies focused on Sub-Saharan Africa, with limited evidence emerging from other endemic regions like Latin America, the Western Pacific, or the Caribbean. These gaps are particularly consequential because economic efficiency does not solely rely on biological impact. It also incorporates local delivery costs, local health system capacity, baseline prevalence patterns, and other factors [7]. With a limited geographical scope, policies are likely to be centered on strategies tailored to scenarios with mismatched epidemiological or economic attributes.

Additionally, differences in methodological approaches were noticed across the studies included in this review, which makes comparability difficult. Expanded coverage scenarios were often associated with more favorable cost-effectiveness ratios in dynamic transmission models, while static cost analyses were more centered on near-term affordability and gave a narrower view. Inconsistent parameter assumptions, especially concerning cure rates, delivery costs, and time frames, make cross-study synthesis challenging as well. The interpretability and relevance of policies derived from cost-effectiveness studies could be improved with more uniform modeling approaches combined with clear sensitivity analyses [19].

One major gap we found in our review is the lack of evidence and intervention among important at-risk groups. Pre-SAC and WRA are, in general, underrepresented in economic evaluations, and cost-effectiveness analyses conducted to date also seem to have completely ignored these critical groups. This gap is concerning in that these groups are especially susceptible to morbidity of STH infections, including stunted growth and development (among Pre-SAC), and anemia [4]. In the absence of economic evidence for these children, policymakers are less able to allocate resources. This makes it more difficult to design targeted interventions for some of the most at-risk groups, ultimately undermining efforts to eliminate STH at the population level.

A key gap in the literature is the limited examination of the long-term sustainability and cost-effectiveness of interventions implemented without concurrent WASH improvements. Many studies evaluate the immediate outcomes of MDA but fail to assess whether the benefits persist, particularly if reinfection rates return to baseline once treatment stops. Sustainable reduction of STH infections requires not only consistent access to medication but also significant environmental improvements that lower the risk of reinfection. The failure to evaluate the combination of WASH with MDA in the long term suggests that these strategies could be only temporally effective. The variability in context and delivery costs across countries was also not consistently accounted for in the included studies. This limits the comparability of findings across settings and highlights the need for future analyses to explicitly incorporate local economic and health system factors when modeling cost-effectiveness.

This scoping review is particularly important for assessing the possible cost-effectiveness of a new FDC of albendazole and ivermectin for STH. Integrated MDA campaigns support the claim that treatments, when combined and delivered in a single delivery event, could significantly reduce cost per person and increase the return on investment. This is particularly true in areas where STH epidemiology calls for both drugs to be used [8]. The FDC’s broader activity could achieve a greater health impact by concurrently eliminating STH and other parasites, thus increasing the DALYs averted per treatment round. Nonetheless, without empirical cost-effectiveness estimates for FDC, modeling will need to account for potential gains in efficiency against uncertainties in manufacturing cost, procurement pricing, and adoption feasibility. The literature suggests that such an intervention would likely be most cost-effective in high-prevalence, co-endemic settings where community-wide coverage is feasible and integration with existing NTD programs can be achieved.

From the reviewed studies, there was a notable absence of costs associated with monitoring and evaluation (M&E) frameworks in the cost-effectiveness analyses. Robust M&E systems are essential to track program coverage, impact, treatment compliance, reinfection dynamics, and the sustainability of the interventions. Integrating M&E costs into cost-effectiveness models would complete the intervention cycle and enable more accurate policy guidance and resource allocation.

Nevertheless, this review has some notable limitations. First, the reliance on English-language publications may have excluded relevant evidence from non-English sources, notably literature from the Americas published in Spanish. Second, the heterogeneity of economic metrics, modeling assumptions, and intervention designs across studies limited our ability to perform direct quantitative comparisons. Finally, given the inclusion of studies spanning more than three decades, differences in global and local economic conditions, inflation, drug pricing, and healthcare infrastructure could influence the comparability of cost-effectiveness results. As a scoping review, we did not perform temporal standardization or inflation adjustments. Therefore, findings should be interpreted as relative rather than absolute economic measures.

In conclusion, this scoping review demonstrates that context has an impact on the cost-effectiveness of STH interventions, with community-wide and integrated MDA strategies typically providing higher economic value than school-based delivery in high-prevalence settings. Improved efficiency was consistently driven by utilizing economies of scale and integrating with other NTD control activities. However, there is uncertainty regarding the generalizability of the findings of this study to other endemic regions due to the fact that the evidence base of the included studies was heavily concentrated in sub-Saharan Africa. Cross-study comparability is further restricted by methodological diversity and inconsistent parameter assumptions. The review also identifies important evidence gaps for interventions that combine environmental and pharmaceutical approaches, as well as for high-risk but underrepresented groups, such as Pre-SAC and WRA.

The findings carry direct relevance for assessing the potential cost-effectiveness of the FDC of albendazole and ivermectin. Experience from integrated MDA campaigns suggests that such a formulation could improve efficiency and impact, particularly in areas with multiple STH burden and high-prevalence contexts where community-wide coverage is achievable. Nonetheless, empirical economic evaluations of FDC for STH control are lacking, highlighting the need for robust modeling and field-based studies to confirm these projections.

Supporting information