BACKGROUND: In England, declining childhood vaccine uptake and related inequalities are causes for concern. Existing evidence suggests challenges accessing services contribute to this decline. This is particularly true for parents facing socioeconomic disadvantage. This study aimed to explore parents' experiences of the vaccination process to generate recommendations for improving the accessibility of childhood vaccination services. METHODS: A longitudinal cohort study was established in May 2023. Sequential interviews were conducted with 22 parents from the birth of their child as they progressed through the vaccination pathway. Data collection comprised life journey interviews and diary keeping. Data were analysed using temporal thematic analysis. RESULTS: Four vaccination trajectories were observed collectively referred to as the 4S Vaccination Trajectory Framework: supported (n = 9), struggled (n = 10), stalled (n = 2), and shunned (n = 1). Three main temporal themes were identified which accounted for the diverging vaccination trajectories: booking systems, the unexpected (e.g., how General Practices managed parents who were late or missed their appointment), and vaccine information provision. For example, many within the 'struggled' trajectory, initiated contact with their General Practice and had considerable difficulty securing appointments due to inflexible booking systems. CONCLUSIONS: To address declining vaccination coverage within England it is vital that vaccine accessibility is improved and that services meet parents' needs. This study deepens our understanding of accessibility issues with the vaccination service and discusses implications for policy and practice.