Vaccine coverage for children is an important indicator of the performance of national health and immunization systems. Most of the existing literature has targeted mothers’ low educational level, living in underserved districts and/or remote rural areas and economic poverty that are correlated with low immunization coverage but the supply- and demand-side constraints to immunization in low- and middle- income countries (LMICs) are not well understood. The reliability of claimed administrative immunization coverage in these contexts is questionable. To address these barriers within the present Expanded Programme on Immunization (EPI), the difficulties related to inadequate vaccination uptake must be addressed in more depth. Building on already produced literature, this study aims to determine the extent of immunization coverage among children in LMICs, as well as to fill in the gaps in awareness about system-level obstacles that currently hinder the effective delivery and uptake of immunization services through EPI. By two reviewers, a literature search using PubMed and Google Scholar along with targeted grey literature was conducted on the 2nd of June 2021 by following PRISMA guidelines. The search techniques for electronic databases used both Medical Subject Headings (Mesh) and free-text words were tailored to each database's specific needs using a controlled vocabulary that was limited to the English language from 2000 and 2020. Of the 689 records, eleven articles were included in this review meeting the inclusion criteria. In total, five articles related to vaccination coverage, four studies on components of the routine immunization system, one article on the implementation of new and under-utilized vaccines and one were on vaccines financing. We evaluated the quality of the included studies and extracted into tables created by one investigator and double-checked by another. Review findings suggest that specific strategies to reduce inequality may be required. Vaccine procurement and pricing strategies, as well as vaccine customization to meet the needs of LMICs, are all critical components in strengthening immunization systems. Our findings could be used to establish practical strategies for countries and development partners to address coverage gaps and improve vaccination system effectiveness.