Undocumented migrants are a vulnerable population group in the context of the COVID-19 pandemic due to increased risk of infection, severe morbidity, and mortality. In this Personal View, we analyze the COVID-19 pandemic responses, particularly vaccination campaigns, vis à vis undocumented migrants, and discuss lessons learned. Our empirical observations as clinicians and public health practitioners in Italy, Switzerland, France, and the United States are supplemented by a literature review, and presented through country case studies focusing on Governance, Service Delivery, and Information. We propose recommendations to capitalize on the COVID-19 pandemic response as an entry point to strengthen migrant-sensitive provisions into health system frameworks, by: providing specific guidance in health policies and plans; developing tailored implementation approaches with outreach and mobile services, with translated and socio-culturally adapted information, and engagement of migrant communities and third sector actors; and developing systematic monitoring & evaluation systems with disaggregated migrant data from National Health Service and third sector providers.