(1) Background: Immunisation is a crucial and effective method for preventing infectious diseases, with its success dependent on high immunisation rates to protect under-immunised individuals and promote herd immunity. This qualitative descriptive study is part of a larger explanatory sequential mixed method design that aims to explore factors influencing parents' decision making to complete childhood immunisation in the Eastern Province of Saudi Arabia, a country experiencing disparities in immunisation coverage across its population. (2) Methods: The sample consisted of a subset of participants from the initial quantitative phase, which included a survey on the immunisation attitudes of parents living in Qatif. This initial phase included n = 350 participants, who were over 18, had access to one of the 27 Primary Health Care (PHC) Centres in Qatif, and had a child under 24 months. This paper presents the qualitative-descriptive phase, which used a qualitative survey to gain open-ended responses from parents (n = 20) and analysed using thematic analysis. (3) Results: Participants identified certain vaccines, particularly MMR, as influencing their immunisation practices. Specific factors identified as deterring parents from immunising their children included fear of autism and other developmental delays, concerns about risks and side effects, mistrust in vaccine efficacy, and discouraging information from the media. Parents' immunisation decisions were evidently affected by policy compliance, family and friends, and social networking sites. These factors are explained through the socio-ecological model. Moreover, the COVID-19 pandemic influenced parents' decisions on vaccine completion in terms of perceived barriers, perceived benefits, and perceived trust. (4) Conclusions: By examining the social-ecological factors shaping parents' decisions to immunise their children in the Eastern Province of Saudi Arabia, this research contributes to the literature and informs the Saudi National Childhood Immunisation Programme about factors contributing to childhood immunisation hesitancy, helping to address a critical healthcare issue.
Keywords: Saudi Arabia; childhood immunisation; childhood vaccination; delayed vaccination; public healthcare; vaccine hesitancy.