The Zero-Dose Learning Hub (ZDLH) mechanism is rapidly underway to improve how data and evidence are used to successfully identify and reach the millions of children who have not yet received a single routine vaccine shot, known as “zero-dose” (ZD) children, and the missed communities in which they live. This ZDLH semiannual update informs Gavi, the Vaccine Alliance Board (Gavi Board) and other stakeholders about the mechanism’s work to use evidence to better understand the factors influencing implementation and performance of approaches to identify and reach ZD and under-immunized (UI) children and missed communities.