Childhood immunization barriers and interventions in low- and middle-income countries: A scoping review of access, delivery systems, and health literacy

ABSTRACT

Childhood immunization is among the most effective public health measures for preventing infectious diseases and reducing child mortality, yet coverage in many low- and middle-income countries (LMICs) remains suboptimal due to barriers in access, delivery systems, and caregiver acceptance. This scoping review mapped experimental and quasi-experimental studies from PubMed and Scopus (2000–2024) evaluating interventions to improve childhood immunization across three domains: access to services, distribution and logistics, and health literacy. Thirty-two studies met inclusion criteria. Community outreach, reminder/recall systems, and incentives improved vaccination uptake, timeliness, and completion. Supply-chain optimization and technology-assisted delivery enhanced vaccine availability and reduced stock-outs, especially in hard-to-reach settings. Educational and culturally tailored communication interventions strengthened caregiver knowledge and confidence. The findings demonstrate that coordinated strategies addressing both supply-side and demand-side constraints are most effective for achieving equitable and sustainable improvements in routine childhood immunization.

Introduction

Childhood immunization is one of the most effective public health interventions for reducing child mortality and preventing life-threatening infectious diseases.¹ Over the past five decades, global vaccination efforts have saved an estimated 154 million lives, with the greatest gains occurring in low- and middle-income countries (LMICs) through the World Health Organization (WHO) Expanded Programme on Immunization.² Vaccines such as Bacillus Calmette-Guérin (BCG), Diphtheria-Tetanus-Pertussis (DTP), Oral Polio Vaccine (OPV), Measles-Containing Vaccine (MCV) have substantially reduced vaccine-preventable mortality worldwide.³ Nevertheless, many children in LMICs remain under-immunized or unvaccinated, highlighting persistent challenges in achieving equitable vaccination coverage.^4,5

Vaccination programs prevented an estimated 37 million deaths between 2000 and 2019, yet substantial coverage gaps persist for key antigens such as measles and pneumococcal conjugate vaccines.^6,7 Coverage gaps persist for key antigens such as measles and pneumococcal conjugate vaccines, contributing to preventable morbidity and mortality in these populations.⁷ These gaps reflect interacting along the immunization delivery continuum. On the supply side, weaknesses in vaccine logistics, cold-chain infrastructure, and service readiness directly limit vaccine availability at the point of care.⁸ On the demand side, caregiver decision-making is shaped by behavioral and social factors, including knowledge, risk perception, confidence, and trust, as reflected in the WHO Behavioral and Social Drivers (BeSD) framework.^9–11 Together, these supply- and demand-side barriers contribute to persistent inequalities in childhood immunization uptake and coverage in LMICs.

In practice, the interaction of supply-side and demand-side barriers manifests through multiple, interconnected constraints that limit childhood immunization performance in LMICs.¹² Limited access to vaccination services remains a major barrier due to weak health-care infrastructure and last-mile delivery challenges, particularly in remote and underserved areas.¹³ These gaps are especially pronounced in parts of West and Central Africa, where millions of children remain unprotected against vaccine-preventable diseases such as diphtheria, tetanus, and pertussis despite vaccine availability.¹⁴ On the supply side, vaccine distribution systems face substantial logistical constraints related to cold-chain maintenance, storage capacity, transportation, and unreliable power supply, which compromise vaccine potency and disrupt reliable delivery, leading to missed vaccination opportunities even where community demand exists.^15–17 On the demand side, caregiver acceptance and timely utilization of immunization services are constrained by behavioral and social factors, including concerns about vaccine safety, limited awareness of vaccination schedules, fear of adverse events following immunization, misinformation, and low trust in health systems.¹⁸ As illustrated in Figure 1, these supply-side and demand-side domains jointly influence vaccination uptake at the individual level and, in turn, population-level immunization coverage in LMICs.

Figure 1.

Conceptual framework illustrating how supply-side and demand-side intervention domains influence childhood immunization uptake and population-level coverage in LMICs.

Several studies have examined specific dimensions of childhood immunization, including health system barriers, educational interventions, and facility-based strategies. For example, Essa-Hadad et al. focused on health system barriers and enablers to measles–mumps–rubella and human papillomavirus vaccination among disadvantaged populations,¹⁹ while Reifferscheid et al. reviewed hospital-based strategies such as patient education and reminder systems to improve childhood immunization coverage.²⁰ Other studies have concentrated mainly on caregiver-focused educational interventions. Notably, Lungeni et al. synthesized evidence on parental education strategies in LMICs but did not integrate considerations of vaccine delivery systems, logistics, or access-related constraints into their review.²¹

Despite the growing body of literature on childhood immunization, existing reviews remain limited in scope and analytical integration. Most reviews focus on discrete components of immunization systems, such as health system barriers, caregiver education, or facility-based strategies, without integrating supply-side and demand-side determinants. As a result, the combined influence of access to vaccination services, delivery systems and logistics, and health literacy interventions on immunization outcomes in LMICs remains insufficiently mapped in the existing literature. In this scoping review, these determinants are examined through three complementary domains, access to vaccination services, delivery systems and logistics, and health literacy interventions, which together provide the conceptual framework for analyzing interventions aimed at improving childhood immunization outcomes in LMICs. Given the diversity of intervention types, study designs, and reported outcomes in this field, a scoping review approach was considered most appropriate to map the breadth of available evidence and identify key research gaps. By integrating evidence across supply-side and demand-side intervention areas, this review is intended to inform more coordinated, context-responsive strategies to strengthen immunization programs and support equitable and sustainable improvements in childhood immunization coverage.

Methods

Study design

This study was conducted as a scoping review to map and synthesize evidence on interventions addressing access to vaccination services, delivery systems and logistics, and health literacy for childhood immunization in LMICs. A scoping review approach was selected to comprehensively map heterogeneous intervention evidence across multiple health system domains and study designs, where the purpose was to identify key concepts, types of interventions, and knowledge gaps rather than to assess intervention effectiveness. This scoping review was conducted and reported in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) guidelines. A completed PRISMA-ScR checklist can be seen in Supplementary File 1. Additionally, the review protocol was registered on the Open Science Framework (OSF) to enhance methodological transparency.²² No substantive deviations from the registered protocol occurred during the conduct of this review.

Search strategy

A systematic literature search was conducted in two electronic databases, PubMed and Scopus. Given that this review focused on experimental and quasi-experimental intervention studies typically indexed in bibliographic databases, PubMed and Scopus were considered appropriate sources for identifying relevant evidence, and citation tracking (forward or backward reference searching) was not systematically conducted. Additionally, gray literature sources were not searched as the review prioritized peer-reviewed intervention studies. The search strategy combined keywords and controlled vocabulary related to: (1) immunization and vaccination; (2) access to services, uptake, delivery systems and logistics, and health literacy; (3) population (children under 18 y of age, caregivers, and health-care providers); (4) study design; and (5) LMIC settings. The full search strategy is provided in Supplementary File 2 Table S1.

Eligibility criteria

We included experimental and quasi-experimental studies evaluating interventions implemented in LMICs to improve childhood immunization through one or more of the following domains: access to vaccination services, delivery systems and logistics, and health literacy. Eligible studies were published in English between 2000 and 2024. Studies were excluded if they: (1) did not report immunization-related outcomes of interest; (2) employed study designs not aligned with the review scope (e.g., purely observational designs such as cross-sectional, cohort, or descriptive studies), which were excluded to maintain a focus on evaluated interventions with direct policy and implementation relevance; (3) were reviews, systematic reviews, commentaries, editorials, or study protocols; or (4) were conducted in non-LMIC settings. Full operational details of the eligibility criteria are presented in Table 1.

Table 1.

Eligibility criteria of included studies.

Criteria	Description
Study design	Experimental studies, including randomized controlled trials (RCTs) and non-randomized controlled trials Quasi-experimental studies, including pre–post (before–after) designs and interrupted time-series studies
Population	Children that were under 18 y of age receiving immunization, caregivers, and healthcare providers in low middle income countries.
Intervention	Any program strategy or intervention implemented by government or community to improve access, coverage, distribution/logistics, or health literacy of childhood vaccination, including: Health education Patient reminder or recall system Household monetary or non-monetary incentives Home visit Training for healthcare providers Multi-faceted interventions Logistic support and supply-chain support Other relevant strategies
Comparator	Routine care or standard practice
Outcome	Immunization-related outcomes, including vaccination uptake, coverage, timeliness, service availability, and caregiver knowledge, acceptance, or confidence.
Databases	Pubmed and Scopus
Publication period	2000–2024

Study selection and data extraction

All records retrieved from the database searches were exported to Mendeley for reference management and duplicate removal. Two reviewers (YF and MQ) independently screened titles and abstracts for eligibility, followed by independently full-text screening of potentially relevant articles. Formal inter-rater agreement statistics (e.g., Cohen’s kappa) were not calculated. Discrepancies between the two reviewers were first resolved through discussion were first resolved through discussion; when consensus could not be reached, a third reviewer (WNI) was consulted to make the final decision. Data extraction was performed using a standardized data extraction form developed in Microsoft Excel. The form was pilot-tested on a subset of included studies and iteratively refined during the review process to ensure that all relevant information was captured. Interventions then were subsequently categorized into three thematic domains: access to vaccination services, delivery systems and logistics, and health literacy, using a deductive coding approach based on the conceptual framework guiding this review. Extracted information included: (1) study characteristics (author, year of publication, country, study design, sample size, and implementing organization); (2) intervention characteristics (intervention type, comparator, and intervention domain); and (3) reported immunization-related outcomes and key findings. Visualization of the geographic distribution of included studies was generated using Tableau software.²³

Data synthesis

The extracted data were synthesized using a narrative and descriptive approach, consistent with the objectives of a scoping review. The synthesis framework was conceptually around the primary intervention domains addressed, access to vaccination services, delivery systems and logistics, and health literacy, identifying patterns in the distribution of studies and highlight areas where evidence remains limited. The included studies were summarized by study design, setting, population, intervention characteristics, and reported immunization-related outcomes. Findings were organized to highlight patterns, similarities, and differences across intervention types and contexts, with particular attention to how supply-side and demand-side strategies were implemented and combined.

Results

Study identification

The database search identified a total of 471 records, of which 279 (59.2%) were retrieved from PubMed and 192 (40.8%) from Scopus. After removal of 15 duplicate records (3.2%), 456 studies were retained for title and abstract screening. During this screening stage, 326 studies (71.5%) were excluded. The full texts of the remaining 130 studies (28.5%) were assessed for eligibility, resulting in the exclusion of 99 articles (76.2%). The primary reasons for exclusion were irrelevant outcomes (n = 35; 35.4%), inappropriate study designs such as cross-sectional, cohort, or descriptive studies (n = 11; 11.1%), study protocols (n = 16; 16.2%), literature or systematic reviews, commentaries, or editorials (n = 24; 24.2%), studies conducted in non-LMIC settings (n = 11; 11.1%), and irretrievable full texts (n = 2; 2%). In addition, one study was identified through reference list screening. Ultimately, 32 studies (24.6% of full-text articles assessed) met the inclusion criteria. The study selection process is illustrated in Figure 2.

Figure 2.

PRISMA diagram of the study selection process for the scoping review of interventions to improve childhood immunization in low- and middle-income countries.

Characteristics of included studies

The included studies were grouped into three intervention domains, delivery systems and logistics, access-related interventions, and health literacy–related interventions, based on the primary mechanism through which they aimed to improve childhood immunization outcomes. These domains reflect different categories of determinants influencing childhood immunization outcomes, including structural determinants related to service delivery and access, as well as informational and behavioral determinants addressed through health literacy–focused interventions. Three studies evaluated delivery systems and logistics–related interventions.^24,25 All studies (100%, 3/3) used quasi-experimental designs and were conducted in India, Benin, and Mozambique. Interventions focused on supportive supervision of frontline health workers,²⁴ and supply-chain optimization.²⁵ Primary outcomes included service quality and vaccination coverage,²⁴ as well as vaccine availability, DTP3 coverage, and supply-chain performance.²⁵ Two studies (67%, 2/3) reported positive effects on immunization outcomes,²⁵ while one study (33%, 1/3) demonstrated mixed effects, with improvements in service quality but limited gains in coverage.²⁴

A total of 21 studies evaluated access-related interventions aimed at improving childhood immunization outcomes.^26–45 The majority were conducted in low- and middle-income countries, predominantly in sub-Saharan Africa (57%, 12/21) and South Asia (38%, 8/21), with one study from Southeast Asia (5%, 1/21). Most studies employed quasi-experimental designs (67%, 14/21), including pre–post evaluations and interrupted time-series,^26,27,30,39 while randomized controlled trials accounted for 19% (4/21) of studies.^32,35,42,45 The remaining studies used non-randomized controlled or pilot designs. Interventions primarily targeted access barriers, including decentralized planning and health system strengthening,^26,27,34 community-based outreach and mobilization,^29,33,36 and digital or mobile health strategies such as SMS reminders, electronic immunization registries, and mobile phone–enabled follow-up systems.^{29,30,32,40,41} Several studies also incorporated incentive-based strategies, including conditional cash transfers,²⁸ and compliance-linked incentives.³⁵ Across studies, children under two years of age and their caregivers were the primary target populations, with outcomes most commonly assessing full immunization coverage, timeliness of vaccination, and uptake of specific antigens such as DPT3, measles, and hepatitis B birth dose. Overall, positive effects were reported in 90% (19/21) of studies, demonstrating improvements in coverage, timeliness, or completion rates. Mixed effects were observed in 10% (2/21) of studies, typically reflecting improvements in coverage without consistent gains in timeliness or sustainability.^34,41 Eight studies examined health literacy–related interventions to improve childhood immunization outcomes.^46–53 Most were conducted in Nigeria (4/8, 50%) and Indonesia (3/8, 37.5%), with one study from India (1/8, 12.5%). Half of the studies used randomized controlled trials (4/8, 50%), while the remainder applied quasi-experimental designs. Interventions primarily targeted mothers, caregivers, and pregnant women, and included home-based health information visits, participatory training, video-based education, SMS-based mHealth reminders, WhatsApp-delivered educational videos, and school-based health education.^46,48–52 Overall, 87.5% of studies (7/8) reported positive effects on outcomes such as vaccine uptake, timeliness, caregiver knowledge, or reduced vaccine hesitancy, while one study (12.5%) reported mixed effects, with loss-framed messaging associated with reduced tetanus vaccine uptake in some groups.⁴⁷ Across included studies, heterogeneity in reported effects frequently reflected variation in outcome measures (e.g., vaccination coverage, timeliness, caregiver knowledge, or vaccine hesitancy), the vaccine types assessed (such as DPT-containing vaccines, measles, hepatitis B, or BCG), and implementation context, rather than inconsistency in the underlying effectiveness of the interventions. Key study characteristics across these domains are summarized in Table 2, with detailed implementation features and quantitative findings presented in Supplementary File 2 Table S2, and the geographic distribution of included studies illustrated in Figure 3.

Table 2.

Characteristics of included studies across intervention domains to improve childhood immunization outcomes.

Author (year)	Country	Study design	Type of intervention	Target population	Primary outcome(s)	Key direction of effect
Delivery systems & logistics
Panda et al. (2015)22	India	Quasi-experimental	Supportive supervision	• Supervisors • Frontline health workers	• Quality of immunization services • Vaccination coverage	Mixeda
Prosser et al. (2017)23	Benin	Quasi-experimental	Supply-chain optimization	Health facilities involved in vaccine distribution	• Effective vaccine management indicators • Vaccine availability	Positive
Prosser et al. (2017)23	Mozambique	Quasi-experimental	Supply-chain optimization	Health facilities involved in vaccine distribution	• DTP3 coverage • Vaccine stockouts • Supply-chain performance	Positive
Access-related interventions
Prinja et al. (2010)24	India	Quasi-experimental (pre–post)	Decentralized planning and microplanning	• Children <18 months • Rural communities	• Age-appropriate DPT coverage • Timeliness of vaccination	Positive
Carnell et al. (2014)25	Ethiopia	Quasi-experimental	Health system strengthening & community engagement	• Households • Children aged 0–23 months	• DPT3 coverage • Measles coverage	Positive
Carvalho et al. (2014)26	India	Quasi-experimental	Conditional cash transfer (JSY)	• Mothers • Children	• Childhood immunization rates	Positive
Ali et al. (2015)27	Pakistan	Quasi-experimental	Community-based immunization support	• Household heads (fathers) • Parents/caregivers	• Immunization knowledge and practices • Full immunization coverage	Positive
Uddin et al. (2016)28	Bangladesh	Quasi-experimental (pre–post)	Mobile phone–based registration and reminder system (mTika)	• Children aged 0–11 months • Caregivers in rural and urban settings	• Full immunization coverage	Positive
Xeuatvongsa et al. (2016)29	Laos	Quasi-experimental pilot	Provision of mobile phones and phone credits to VHV and HCWs	• Children aged 0–9 months • Children aged 12–21 months	• Hepatitis B birth-dose coverage • Postnatal home visits	Positive
Brown et al. (2016)30	Nigeria	Group randomized controlled trial	Cell phone reminder/recall + provider training	• Infants aged 0–12 weeks • Mothers	• Routine immunization completion at 12 months	Positive
Nzioki et al. (2017)31	Kenya	Quasi-experimental (pre–post)	CHW-led primary health care intervention	• Infants aged ≤1 y	• Infant vaccination coverage	Positive
Manyazewal et al. (2018)32	Ethiopia	Quasi-experimental	Health system strengthening (training, supervision, PDCA cycle)	• Healthcare facilities • Children	• Coverage of pentavalent, measles, BCG, PCV	Mixedb
Seth et al. (2018)33	India	Randomized controlled trial	Mobile phone reminders with compliance-linked incentives	Infants (0–24 months)	• Immunization coverage • Timeliness of vaccination	Positive
Dougherty et al. (2020)34	Nigeria	Quasi-experimental study	Engagement of traditional barbers to promote vaccination	• Mothers • Infants (0–5 months)	• Vaccination uptake	Positive
Buser et al. (2021)35	Zambia	Quasi-experimental study	Maternity Waiting Home (MWH) Core model	Mothers who gave birth	• ANC and PNC attendance • Newborn vaccination rates	Positive
Choudhary et al. (2021)36	India	Quasi-experimental	Community-level social mobilization (CLSM) for polio SIAs	Children	Polio SIA booth vaccination coverage	Positive
Clarke-Deelder et al. (2021)37	India	Quasi-experimental	Intensified Mission Indradhanush (IMI)	Infants and young children	• Number of vaccine doses delivered • Coverage of infant vaccines	Positive
Oladepo et al. (2021)38	Nigeria	Quasi-experimental	SMS vaccination reminders	Mothers of infants (0–2 months)	Full and timely immunization completion	Positive
Dolan et al. (2022)39	Tanzania	Interrupted time-series	Electronic immunization registry (EIR)	Children eligible for routine immunization	• On-time vaccination • Vaccination timeliness	Mixedc
Yunusa et al. (2022)40	Nigeria	Randomized controlled trial	Cell phone reminder/recall; PHCIPT; combined intervention	Children aged 0–12 months and mothers	Immunization completion rate	Positive
Bakkabulindi et al. (2023)41	Uganda	Quasi-experimental	Monthly immunization data audits with CHWs	Infants under 1 y	Vaccination coverage (BCG, DTP3)	Positive
Sowe et al. (2023)27	Gambia	Controlled interrupted time series	SMS-based monitoring of vaccination timeliness	• Health facilities • Newborns	Hepatitis B birth dose timeliness	Positive
Yau et al. (2023)42	Nigeria	Non-randomized controlled trial	Color-coded bracelets and peer mobilizers	Newborns (0–14 d)	• Vaccination timeliness • Vaccination completeness	Positive
O’Neill et al. (2024)43	India	Randomized controlled trial	Door-to-door health education using gain- vs loss-framed messaging	Mothers of children aged 0–36 months	• Uptake of DPT3 • Uptake of measles vaccine	Positive
Health literacy–related interventions
Powell-Jackson et al. (2018)44	India	Randomized controlled trial	Health information messages delivered through home visits	Mothers of unvaccinated or incompletely vaccinated children aged 0–36 months	• DPT3 uptake • Full immunization	Positive
Sato & Takasaki (2021)45	Nigeria	Randomized controlled trial	Loss-framed (“scared-straight”) health messages with cash incentives	Women of childbearing age (15–35 y)	• Tetanus vaccine uptake • Risk perceptions	Mixedd
Balogun et al. (2021)46	Nigeria	Quasi-experimental (pre–post)	Intensive participatory training using manuals and video	Older women (≥35 y) supervising childcare	Knowledge and support for infant vaccination	Positive
Aisyah et al. (2022)47	Indonesia	Quasi-experimental	Video-based education and wheel vaccination calendar	Caregivers of children aged 0–23 months	Health literacy related to childhood vaccination	Positive
Balogun et al. (2022)51	Nigeria	Randomized controlled trial	Training caregivers on importance of timely and complete infant vaccination with supervised follow-up	Pregnant women and caregivers	Timeliness and completion of infant vaccinations (birth–9 months)	Positive
Lenel et al. (2022)48	Indonesia	Randomized controlled trial	SMS-based mHealth reminders and behavioral nudges	Mothers and infants	Maternal health behaviors including child vaccination	Positive
Lubis et al. (2022)49	Indonesia	Quasi-experimental	Educational immunization videos distributed via WhatsApp groups	Parents and infants	Reduction in vaccine hesitancy	Positive
Olaoye et al. (2024)50	Nigeria	Quasi-experimental (pre–post)	Theory-based HBV infection prevention education (teacher-, peer-, combined delivery)	Secondary school students	Improvement in HBV infection prevention practices	Positive

^aimprovements observed in service quality indicators, while changes in vaccination coverage were modest or not clearly attributable to the intervention alone.

^bimprovements observed for several antigens, but not statistically significant for full immunization coverage.

^cOverall decline in on-time vaccination; subgroup improvement among fully registered children.

^dimprove awareness and emotional response but can negatively affect vaccination behavior if not paired with supportive, confidence-building information.

Abbreviations: ANC, antenatal care; BCG, Bacillus Calmette–Guérin vaccine; CD(s), control district(s); CHW(s), community health worker(s); CI, confidence interval; CLSM, community-level social mobilization; DPT, diphtheria–pertussis–tetanus vaccine; DPT3, third dose of diphtheria–pertussis–tetanus vaccine; E1/E2/E3, experimental groups 1, 2, and 3; EIR, electronic immunization registry; EVM, effective vaccine management; HBV, hepatitis B virus; HCW(s), health care worker(s); HepB-BD, hepatitis B birth dose; ID(s), intervention district(s); IMI, Intensified Mission Indradhanush; ITS, interrupted time series; IVC, infant vaccination coverage; JSY, Janani Suraksha Yojana; mHealth, mobile health; mTika, mobile-based vaccination tracking and reminder system; MWH, maternity waiting home; PCV, pneumococcal conjugate vaccine; PDCA, Plan–Do–Check–Act; PHC, primary health care; PHCIPT, primary health care immunization providers’ training; PIRI, periodic intensification of routine immunization; PNC, postnatal care; PPM, peer-to-peer mobilizers; R/R, reminder/recall; RR, relative risk; SIA(s), supplementary immunization activity(ies); SMS, short message service; SS, supportive supervision; UNICEF, United Nations Children’s Fund; VHV(s), village health volunteer(s); WHO, World Health Organization.

Figure 3.

Geographic distribution of included studies for the scoping review of interventions to improve childhood immunization in low- and middle-income countries.

Logistic and distributions-related interventions

Three studies focused on strengthening delivery systems and logistics to improve childhood immunization outcomes by addressing supervisory practices and supply-chain performance. All interventions targeted system-level bottlenecks within routine immunization programs, with implementation at district, facility, or national levels. In India, enhanced supportive supervision of frontline health workers improved service quality indicators, although gains in vaccination coverage were limited, resulting in mixed effects overall.²⁴ In contrast, two quasi-experimental studies conducted in Benin and Mozambique demonstrated consistently positive effects following supply-chain optimization interventions guided by Effective Vaccine Management (EVM) indicators.^24,25 These interventions improved vaccine availability, strengthened distribution performance, and substantially reduced stockouts, with associated increases in DTP3 coverage in Mozambique.

Access-related interventions

Access-related interventions constituted the largest group of included studies. These interventions were implemented across multiple levels of the health system, including health service organization, community outreach, financial incentives, and digital service delivery platforms.^31,40 Overall, access-focused strategies were associated with improvements in vaccination coverage, timeliness, and completion across diverse LMIC settings.^27,44

Health system strengthening and service delivery optimization were common approaches. In India, decentralized planning and enhanced microplanning improved age-appropriate DPT coverage and reduced delays in vaccination.²⁶ In Ethiopia, a comprehensive intervention combining health system strengthening with community engagement resulted in significant increases in DTP3 and measles coverage.²⁷ Similarly, a Community Health Worker–led primary health care intervention in Kenya increased infant vaccination coverage at the community level.³³

Financial and demand-side incentives also contributed to improved access. In India, the Janani Suraksha Yojana conditional cash transfer program increased childhood immunization coverage across multiple antigens, with the strongest effects observed for full immunization.²⁸ Another Indian study demonstrated that compliance-linked incentives combined with mobile phone reminders improved both immunization coverage and timeliness.³⁵

Digital health interventions were widely used to reduce missed opportunities for vaccination. In Bangladesh, a mobile phone–based child registration and reminder system substantially increased full immunization coverage in both rural and urban populations.³⁵ In Nigeria, combined cell phone reminder/recall and provider training interventions achieved significantly higher completion rates compared with usual care.^32,42 SMS-based monitoring systems in The Gambia improved vaccination timeliness, particularly in lower-performing facilities.²⁹ Electronic immunization registries introduced in Tanzania produced mixed overall effects, though improvements in on-time vaccination were observed among fully registered children.⁴¹

Community-based access interventions further strengthened service utilization. In Pakistan, enhanced community outreach targeting household heads increased full immunization coverage.²⁹ In Nigeria, engagement of traditional barbers as community referral agents significantly increased newborn vaccination uptake.³⁶ Large-scale social mobilization initiatives were also effective; community-level mobilization efforts in India prevented declines in polio supplementary immunization activity coverage,³⁸ while Intensified Mission Indradhanush increased delivery of multiple infant vaccines, particularly among under-immunized populations.³⁹ Facility-based innovations, such as maternity waiting homes in Zambia, additionally supported continuity of care and improved newborn vaccination coverage.³⁷

Health literacy-related interventions

Eight studies primarily targeted caregiver knowledge, attitudes, communication, and trust. These interventions employed interpersonal education, trusted community messengers, visual learning tools, and digital communication platforms to influence vaccination behaviors.^48,50,52

In India, structured home visits delivering tailored immunization information significantly increased DPT3 uptake and full immunization coverage by approximately 14% points.⁴⁶ Similarly, door-to-door health education using framed messaging led to sustained improvements in DPT3 and measles vaccine uptake, with increases of up to 15.2 and 22% points, respectively.⁴⁵ In Nigeria, participatory training of caregivers and supervising family members improved vaccination-related knowledge and support for infant immunization.⁴⁸

Educational immunization videos disseminated via WhatsApp significantly reduced vaccine hesitancy among caregivers, from 10.3% to 6.9%.⁵¹ Video-based education combined with vaccination calendars improved caregiver understanding and tracking of immunization schedules.⁴⁹ SMS-based mHealth reminders and behavioral nudges were also associated with improved maternal health behaviors, including child vaccination.⁵⁰

In Nigeria, intensive training of caregivers combined with supervised follow-up significantly improved timely and complete infant vaccination, with coverage reaching 67.9% in the intervention group compared with 36.6% in controls.⁴⁸ School-based health education targeting adolescents improved hepatitis B infection prevention practices, though vaccination uptake was not directly measured.⁵²

A randomized trial from Nigeria showed that loss-framed (“scared-straight”) messaging combined with financial incentives reduced tetanus vaccine uptake among some subgroups, indicating a potential backfire effect when fear-based communication is not accompanied by supportive or empowering messaging.⁴⁷

Discussion

This scoping review synthesizes evidence on interventions to improve childhood immunization outcomes in LMICs across three interconnected domains: access to vaccination services, delivery systems and logistics, and health literacy and acceptance. Overall, the findings indicate that while interventions targeting individual domains can improve vaccination uptake, timeliness, or service availability, the most consistent and sustained improvements were observed when supply-side and demand-side strategies were implemented in combination. Interventions that strengthened vaccine delivery and access were most effective when accompanied by efforts to improve caregiver knowledge, trust, and engagement, underscoring the interdependence of service readiness and vaccine acceptance.

The delivery systems and logistics interventions identified in this review focused on correcting operational weaknesses within routine immunization programs, including deficiencies in supervision, cold-chain functionality, and supply-chain governance. Evidence from multiple settings indicates that these system-level interventions improved vaccine availability and reduced stock-outs, with downstream effects on coverage for key antigens such as DTP3. However, improvements in logistical performance alone did not uniformly translate into proportional gains in vaccination coverage, reflecting broader evidence that supply-side strengthening is necessary but insufficient when demand-side and access constraints persist.⁵⁴ Supportive supervision interventions similarly demonstrated improvements in service quality but produced mixed effects on coverage outcomes, suggesting that provider-focused quality improvements must be embedded within broader system optimization efforts to achieve population-level impact.⁵⁵ Technological innovations, including drone-supported vaccine delivery, have emerged as promising approaches to overcoming geographic and last-mile barriers in hard-to-reach areas, with evidence indicating improved supply reliability and downstream child health benefits when such technologies are integrated into national distribution systems.⁵⁶ Nevertheless, the effectiveness and sustainability of technology-driven solutions depend on their alignment with existing cold-chain infrastructure, inventory management capacity, and governance mechanisms, as emphasized in broader analyses of immunization system performance in LMICs.⁵⁷

Although strengthened delivery systems and logistics are essential for ensuring vaccine availability, they are insufficient on their own to guarantee that children can consistently access and complete routine immunization services. Access-related interventions therefore play a critical role in translating vaccine availability into actual service utilization by addressing structural and systemic barriers that limit caregivers’ ability to reach and complete immunization services.⁵⁸ Evidence from broader analyses of immunization system performance in LMICs indicates that geographic distance, service organization, health workforce distribution, and opportunity costs remain major determinants of incomplete and delayed vaccination, even in settings with adequate vaccine supply.⁵⁹ In addition, immunization coverage may be particularly vulnerable in fragile and conflict-affected settings and among displaced populations, including infants living in refugee or temporary settlements.⁶⁰ Disruptions to health infrastructure, population mobility, and limited access to routine health services can reduce vaccination uptake and increase the number of “zero-dose” children in these contexts.⁶¹ These conditions highlight the need for tailored immunization strategies that address the unique operational and access challenges faced by humanitarian and displacement-affected populations.

Approaches that strengthen service delivery organization, decentralize planning, and expand community-based outreach are thus central to improving routine immunization performance, particularly among underserved populations.⁶² Digital health tools, including mobile-based registration, reminder, and tracking systems, have demonstrated potential to reduce missed opportunities for vaccination and improve continuity of care⁶³; however, their effectiveness depends on data quality, health worker capacity, and integration within routine health system workflows rather than stand-alone deployment.^64,65 Economic and logistical constraints faced by caregivers, such as transportation costs and time away from work, further shape access to immunization services, underscoring the importance of access-oriented policies that reduce indirect costs and improve convenience alongside service availability.^66,67 However, even when services are physically accessible and operationally efficient, sustained improvements in childhood immunization coverage depend on caregivers’ willingness, confidence, and ability to engage with vaccination services.

Sustained improvements in childhood immunization coverage depend not only on service delivery and access, but also on caregivers’ knowledge, confidence, and trust in vaccination services. Limited understanding of immunization schedules, concerns about vaccine safety, fear of adverse events, and low trust in health systems continue to constrain vaccine uptake even where services are available.^68–70 These findings are consistent with the WHO’s BeSD framework, which underscores the central role of confidence, social influence, and practical considerations in shaping vaccination behavior.¹⁰ Interventions that focus solely on information provision without addressing these broader determinants have therefore shown limited and inconsistent effects across diverse contexts. In contrast, approaches that employ culturally responsive communication, leverage trusted community actors, and reinforce caregivers’ self-efficacy and social support have been associated with more durable improvements in vaccine acceptance and completion.⁷¹ Poorly designed communication strategies, particularly fear-based or loss-framed messaging, may erode trust and discourage vaccination when not accompanied by supportive, confidence-building information, underscoring the importance of grounding demand-side interventions in behavioral science principles.^72,73

Across the three intervention domains examined in this review, a consistent pattern emerges whereby improvements in childhood immunization outcomes in LMICs depend on the alignment of supply-side system readiness with demand-side engagement and service utilization. Strengthened delivery systems and logistics ensure vaccine availability, but without adequate access mechanisms and caregiver engagement, gains in supply are unlikely to translate into coverage improvements.^74,75 Similarly, access-oriented strategies that reduce physical, financial, or organizational barriers are constrained when vaccine supply is unreliable or when caregivers lack trust, confidence, or the capacity to navigate services.⁷⁶ This interdependence reflects broader health systems evidence indicating that immunization performance is shaped by interactions across service delivery, health workforce capacity, community engagement, and governance structures rather than by isolated interventions.^77,78 Importantly, the findings suggest that interventions spanning multiple domains, such as those that combine reliable supply chains, community-based service delivery, and culturally responsive communication, are better positioned to produce sustained and equitable improvements in immunization coverage than single-component approaches. As such, childhood immunization in LMICs should be conceptualized and addressed as a system-level challenge, requiring coordinated strategies that operate across logistical, access-related, and behavioral dimensions.⁷⁹

The cross-domain nature of the findings has clear implications for health policy and immunization program design in LMICs. The evidence suggests that national immunization strategies may benefit from integrated policy frameworks that simultaneously strengthen supply-chain governance, organize service delivery to reduce physical and financial barriers, and embed trust-building and culturally responsive communication within routine immunization services.^80–82 Evidence from health systems and implementation research further indicates that institutionalizing community-based delivery platforms, supported by frontline health workers and digital monitoring tools, can improve continuity and accountability when aligned with broader system capacity and governance structures.^83,84 At the same time, demand-side policies may need to move beyond information provision to more explicitly address confidence, trust, and social context, in order to ensure that improvements in service availability and access translate into sustained vaccine uptake.^85,86 All these considerations suggest that childhood immunization is best understood as a system-level function shaped by interactions across logistical, access-related, and behavioral domains, rather than as a collection of discrete interventions.⁸⁷

Strengths and limitations

This scoping review has some strengths and limitations. A key strength lies in its integrative synthesis of evidence across delivery systems and logistics, access to vaccination services, and health literacy and acceptance, offering a system-level perspective on childhood immunization in LMICs. Moreover, this study focused on experimental and quasi-experimental studies, providing policy-relevant insights into how supply-side and demand-side factors interact to influence immunization outcomes. However, several limitations should also be considered when interpreting the findings. First, this review may be subject to publication bias and language bias, as the search was limited to studies published in English and conducted in two bibliographic databases (PubMed and Scopus). This approach may have limited the identification of studies indexed in other databases as well as relevant gray literature, including programmatic data and reports available through institutional platforms such as the WHO or UNICEF databases. In addition, the included studies were heterogeneous in design and context, and the evidence base was concentrated in sub-Saharan Africa and South Asia, limiting generalizability to other regions. The absence of studies from some LMIC regions, including North Africa and parts of Latin America, may reflect gaps in the existing evidence base or differences in the types of study designs commonly conducted and published in these settings. Health system structures, immunization program organization, and sociocultural determinants of vaccine uptake may differ substantially across regions such as Latin America, the Middle East, and parts of Southeast Asia. As a result, the effectiveness and implementation feasibility of specific interventions identified in this review may vary depending on local health system capacity, governance structures, and community engagement mechanisms. This review did not perform a formal quality assessment of included studies, consistent with scoping review methodology, which limits conclusions regarding the strength of causal evidence. In addition, the heterogeneity of reported outcome measures and target populations across included studies prevented direct quantitative comparison of immunization coverage across different population groups (e.g., routine childhood vaccination, maternal catch-up campaigns, or fully immunized children). Finally, few studies assessed long-term sustainability, equity impacts, or cost-effectiveness, highlighting important priorities for future research.

Conclusions

Childhood immunization remains a cornerstone of public health, yet coverage in many LMICs is constrained by persistent supply-side and demand-side barriers. This scoping review synthesized experimental and quasi-experimental evidence across delivery systems and logistics, access to vaccination services, and health literacy and acceptance, demonstrating that interventions targeting individual domains can improve specific outcomes, but the most consistent and sustainable gains occur when these domains are addressed in combination. The findings highlight that immunization performance in LMICs is shaped by the interaction of health system capacity, service accessibility, and caregiver trust and engagement rather than by isolated interventions. Future research should prioritize integrated intervention designs, examine long-term sustainability, equity, and cost-effectiveness, and expand evidence generation in underrepresented and fragile settings. Policymakers and program implementers should therefore adopt coordinated, system-oriented immunization strategies that embed reliable delivery systems, accessible services, and culturally responsive, trust-building communication within routine health system structures to achieve equitable and sustained improvements in childhood immunization coverage.

Biography

Auliya A. Suwantika, Professor of Pharmacoeconomics at Universitas Padjadjaran (UNPAD), Bandung, Indonesia, and currently serves as Dean of the Faculty of Pharmacy, UNPAD. He specializes in vaccinology, immunization policy, and health technology assessment, with particular expertise in economic evaluation of vaccines and public health interventions in Indonesia and Southeast Asia. Professor Suwantika has led multiple national and international research projects focusing on improving vaccine uptake, equity in immunization programs, and prioritization of healthcare resources for vulnerable populations. In addition to his academic role, he is affiliated with the Centre of Excellence for Pharmaceutical Care Innovation and the Center for Health Technology Assessment at UNPAD. His work integrates behavioral and social drivers of vaccination with incidence-based cost-effectiveness modeling to support evidence-informed decision-making.

Funding Statement

This publication charge is funded by Unpad through the Indonesian Endowment Fund for Education (LPDP) on behalf of the Indonesian Ministry of Higher Education, Science and Technology and managed under the EQUITY Program (Contract No. 4303/ B3/DT.03.08/2025 and 3927/UN6. RKT/HK.07.00/2025).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

All data presented in the current work are available in the text and supplementary materials and can also be obtained from the authors upon request.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/21645515.2026.2651508