Scoping Review of Implementation Strategies for Reaching Zero-Dose and Under-Immunized Children in Low- and Middle-Income Countries
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Abstract
Background: Reaching zero-dose and under-immunized children is a priority under Immunization Agenda 2030 and essential for equitable immunization coverage and universal health coverage. This review synthesized evidence on interventions and implementation strategies used to reach these children in low- and middle-income countries.
Methods: We conducted a scoping review using Joanna Briggs Institute methodology and reported in accordance with the PRISMA extension for Scoping Reviews. PubMed and Google Scholar were searched for studies published from January 2016 to August 2026. Eligibility was guided by the Population, Concept and Context framework. Data were charted and synthesized descriptively and thematically to identify patterns in strategies, populations, settings, adaptation, and outcomes.
Findings: Of 247 records were retrieved, and 33 studies were included. Most included studies were from the WHO African Region, with Nigeria contributing the largest number of single-country studies (n=17). Strategies were predominantly multicomponent and embedded within routine immunization and primary healthcare structures. Health-system strengthening was most frequent (12 studies, 36.4%), followed by community engagement and social mobilization (10, 30.3%). Digital/information-system and behavioural/communication strategies were each reported in five studies (15.2%). Strategies were adapted through community participation, engagement of local leaders, household mobilization, geospatial planning, and use of local data. Outcomes ranged from improved implementation processes and programme capacity to gains in vaccination uptake, immunization completeness, and identification or vaccination of zero-dose and under-immunized children.
Conclusion: Findings indicate that reaching zero-dose and under-immunized children requires context-specific combinations of strengthened, extended, and adapted routine immunization strategies, rather than a single universally applicable approach.
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