The Zero-Dose Learning Hub (ZDLH) established by Gavi, the Vaccine Alliance, is focused on the outcome of timely, increased, and sustainable use of evidence to improve global, regional, and country immunization programs and policies in alignment with the Gavi 5.0 Strategy and Identify, Reach, Monitor, Measure, and Advocate (IRMMA) Framework. The ZDLH Semiannual Update highlights the consortium’s efforts to generate and use evidence, deepening the understanding of factors that influence the implementation and effectiveness of strategies for reaching zero-dose and under-immunized children, and missed communities. This summary provides brief highlights of the ZDLH's activities as the global learning partner from January–June 2025. See the country reports for a detailed summary of each country’s priorities, activities, progress, and learnings to date.