Introduction: Existing evidence on why children miss vaccines after infancy has focused on the demand side, focusing on the attitudes and circumstances of caregivers. The supply side, meaning the system’s capacity to make vaccines available, accessible, and deliverable, has received less attention, even though it determines whether a willing caregiver can be served. This study examined the supply-side determinants of second-year and newer vaccine uptake in Malawi through a coverage-cascade and bottleneck analysis. Methods: A mixed-methods study drew on a caregiver survey, a survey of frontline health workers, a facility checklist and data quality assessment, and key-informant interviews at facility, district, and national level. Findings were organised through the Tanahashi coverage framework, which follows the steps from the availability of commodities and staff, through geographic access, to service contact and effective coverage. Supply-side constraints in uptake were profiled at each step and set against the coverage achieved for each antigen. Results: Effective coverage fell across the antigen sequence, from 95.9 percent for the second dose of measles-rubella vaccine and 93.1 percent for the second dose of polio vaccine, to 74.6 percent for typhoid, to 63 percent for HPV. Commodity availability was high, with cold chain and vaccines present in every checklist facility, and stock records in 47 of 50, yet a quarter of caregivers had been turned away due to stockouts. Human-resource readiness was weaker, with over half of frontline workers never receiving refresher training. Geographic access constrained a fifth of caregivers, and outreach, though present everywhere, was limited by fuel and, in staff accounts, reduced by the 2025 withdrawal of external funding. The bottleneck was not commodity availability but the contact step and the maintenance of frontline capacity. National respondents placed these constraints within a financing system that is partly donor-dependent and fragmented across separate partner plans. Conclusions: The supply system delivered the established second-year antigens well and faltered for the newer ones and at the point of contact. Sustaining uptake will require protecting stock at the point of need, resourcing outreach, maintaining frontline capacity, and adapting supply for the newer vaccines.