The increasing democratisation of the public health decision-making process and the opening-up of debate to new actors heavily rely upon procedures which provide a platform to enable informed groups such as practitioners or consumer associations and other NGOs to express their opinions. Using the example of a public hearing on BCG vaccination that was organised in November 2006 by the French Society of Public Health, this study questions the role of these new actors in the decision-making process, their weight with regard to expert opinions and their influence on decision-makers. The qualitative thematic analysis of the debates held throughout the public hearing and hearing committee’s deliberations highlights that despite the diversity of the actors present and their level of participation in the debate, the varied nature of the themes addressed and the diverse stance on issues, the consultation process is held according to a relatively restricted format under certain noticeable constraints. Only a well-informed audience, composed of doctors (either clinicians or public health doctors) is apt and capable of contributing to the debate with the full capacity to react to the technical interventions. Their participation is largely dependant on using their own experience from the field as a form of expertise on the subject of vaccination. This study discusses the notion of expertise within public debate, which in order to be truly legitimate, must be accompanied by recognition of the affiliation of the actor as an expert as such.