BackgroundIn Pakistan, immunization coverage has been quite low since the program’s inception, and the 2012–2013 population-based survey recorded it at 54%. Much has been written about the issues, challenges, and constraints in the implementation of Pakistan’s immunization program. However, there is a need to better understand the health system barriers as well as levers that influence progress. This review aims to bridge the information gaps on system-level barriers that currently impede the optimal delivery and uptake of immunization services to the children of Pakistan through the Expanded Program on Immunization (EPI).MethodsWe conducted a comprehensive literature review, using PubMed and Google Scholar to find peer-reviewed literature, and also reviewed EPI-related international and national reports. Additionally, we consulted government reports, surveys, and publications on the health system. Employing the basic tenets of WHO’s health systems framework for health system strengthening, and a socio-ecological model, this study cataloged the service delivery and the demand side perspective on various pillars of Pakistan’s immunization program.ResultsThemes generated from the literature review included financing, governance, service delivery, human resources, information systems, and supplies and vaccines. Findings suggest that certain areas in the larger health system need to be improved for a more coordinated implementation of EPI in Pakistan. Moreover, it is imperative to understand community behaviors and perceptions as well as demand side issues in order to achieve the desired results.ConclusionFor better immunization coverage and ultimately a reduction in child mortality due to preventable diseases, EPI operations and performance must be improved. Further systematic implementation research could help to develop an even finer understanding of the system-wide bottlenecks encumbering the coverage and efficiency of the program.