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Shocks effects are under-theorised in the growing literature on health system resilience. Existing work has focused on the effects of single shocks on discrete elements within the health system, typically at national level. Using qualitative system dynamics, we explored how effects of multiple shocks interacted across system levels and combined with existing vulnerabilities to produce effects on essential health services delivery, through the prism of a case study on childhood vaccination in Lebanon. Lebanon has experienced a series of shocks in recent years, including large-scale refugee arrivals from neighbouring Syria, the COVID-19 pandemic and a political-economic crisis. We developed a causal loop diagram (CLD) to explore the effects of each shock individually, and in combination. The CLD was developed and validated using qualitative data from interviews with 38 stakeholders working in Lebanon's vaccination delivery system, in roles ranging from national level policy to facility-level service delivery, conducted between February 2020 and January 2022. We found that each of the shocks had different effects on service demand- and supply-side dynamics. These effects cascaded from national through to local levels. Both Syrian refugee movement and the COVID-19 pandemic primarily exposed vulnerabilities in service demand, mainly through slowly emerging knock-on effects on vaccination uptake behaviour among host communities, and fear of contracting infection in crowded health facilities respectively. The economic crisis exposed wider system vulnerabilities, including demand for vaccination as household income collapsed, and supply-side effects such as reduced clinic time for vaccination, declining workforce retention, and reduced availability of viable vaccine doses, among others. Finally, important pathways of interaction between shocks were identified, particularly affecting the balance between demand for vaccination through publicly supported facilities and private clinics. Future research should incorporate dynamic approaches to identifying within-system vulnerabilities and their potential impacts under different scenarios, as a precursor to improved resilience measurement, system preparedness, and intervention targeting. • Shocks effects are under-theorised in the health systems literature. • Sequential shocks had interacting effects on vaccination delivery in Lebanon. • These shocks also exposed both demand- and supply-side system vulnerabilities. • Stability in human resourcing and funding flows is key for system resilience. • Dynamic methods can help identify resilience-promoting measures and their effects. [ABSTRACT FROM AUTHOR]