This paper presents an in-depth analysis of the collaboration between Gavi, the Vaccine Alliance, and “la Caixa” Foundation, illustrating a unique public–private partnership that tackled the grand challenge of childhood immunization in developing countries. Using the framework proposed by George et al. (Academy of Management Journal 59:1880–1895, 2016) to examine grand challenges in management research, the study highlights the complexity, uncertainty, and evaluative nature of such challenges. The Gavi—“la Caixa” partnership, initiated in 2008, aimed to combat child mortality through immunization campaigns in low-income regions, particularly in Africa. Over time, the collaboration evolved to include innovative fundraising methods, corporate engagement, and micro-donations, raising over €46.7 million and vaccinating over 10 million children. The partnership navigated significant organizational and institutional barriers, including stagnating donations exacerbated by the COVID-19 pandemic. Despite these challenges, the alliance remained a model of successful multi-stakeholder engagement. This paper contributes to the growing body of research on grand challenges by offering insights into how strategic alliances between public and private entities can drive societal impact and innovation.