 The article highlights that despite being one of the most cost-effective and potentially equitable public health interventions, approximately 19.9 million children worldwide are under-immunized or not vaccinated at all, with Sub-Saharan Africa bearing a disproportionate burden of vaccine-preventable diseases. The article also discusses the challenges faced in improving vaccination coverage rates in Sub-Saharan Africa, which has stagnated at approximately 72% for completion of the primary series of infant vaccines over the past decade. The reasons for under-immunization in Sub-Saharan Africa are identified as multifactorial and may differ between and within countries, highlighting the need for country-specific, possibly at a district or sub-regional level, interrogation of factors contributing to under-immunization of children to work towards providing universal health coverage as envisioned in the Sustainable Development Goals. This article was authored by Shabir A. Matty and Helen Rees.