Recent developments in the United States, the United Kingdom and the European Union suggest that public health is undergoing a crisis that is both infrastructural and epistemic. Taking the 2026 revision of US childhood vaccination recommendations as a focal case, this commentary examines how vaccination has become a privileged terrain for the political weaponisation of scientific uncertainty. We argue that the wider pressures on public health infrastructures cannot be understood only as external attacks on science or as problems of misinformation. They also reflect longer-standing transformations in how evidence is produced, hierarchised and mobilised. Drawing on critiques of evidence-based medicine and evidence-oriented approaches to policy, we show how formal hierarchies of evidence, the privileging of randomised controlled trials, assumptions of generalisability and the authority of quantification can narrow what counts as legitimate knowledge in public health. While these approaches have enhanced rigour, transparency and accountability, they can also marginalise contextual, experiential, historical and social forms of evidence. This restricted epistemic configuration creates openings through which political actors can selectively amplify uncertainty—gaps in trial design, questions of generalisability, or limits in surveillance systems—to undermine collective interventions such as vaccination. We conclude that responding to the current crisis requires more than defending science against misinformation. It requires rebuilding the social, institutional and epistemic conditions through which evidence can be produced, scrutinised, trusted and acted upon as part of a collective public project. Inter- and transdisciplinary collaborations, including meaningful engagement with affected communities and civil society organisations, are essential to generating more plural, reflexive and socially grounded forms of evidence capable of sustaining public health in common.