The Uganda National Expanded Program on Immunisation (UNEPI) has made great strides in improving immunization coverage over the last 20 years. Despite these efforts, challenges in reaching every child with vaccines remain. These challenges are illustrated by the observed increase in the number of zero-dose children (ZDC). To characterize and understand the challenges of reaching the ZDC, under-immunized children, and missed communities, the Uganda Learning Hub for Immunisation Equity conducted a rapid assessment between August 2023 and March 2024 in three districts with high burden of ZDC (Wakiso, Mubende, and Kasese) in Uganda.