In 2008, the Commission on Social Determinants of Health at the World Health Organisation published a report demonstrating the existence of a socio- economic gradient for health. Though health inequalities had been apparent since at least the 19th century, the report introduced a bio-psycho-social aetiological model that was absent from 19th century social medicine, as well as from former WHO documents. To bio-psycho-social epidemiologists stress associated with social status is the main cause of morbidity and death. Here I begin by noting that the history social epidemiologists have written for their field tends to inscribe their work in continuity with 19th century social medicine. This contributes towards minimizing the epistemological and contextual transformations that led bio-psycho-social epidemiology to initiate a profound transformation in international health policy. Adopting an epistemological and transnational perspective, I firstly argue that bio-psycho- social epidemiology emerged from René Dubos’ historical and epistemological critique of the foundation of 19th century social medicine. I secondly show how the political and epistemological research program elaborated by Dubos developed in the US context, which was characterized both by a growing concern for chronic diseases and for racial inequalities. Finally, I show that through its transnational circulation in the United Kingdom, bio-psycho-social epidemiology was “de-racialized”. This step was a prerequisite for its aetiological model to be integrated into international public health strategies and to transform them.