This paper presents a socially adaptive virtual agent that can adapt its behaviour according to social constructs (e.g. attitude, relationship) that are updated depending on the behaviour of its interlocutor. We consider the context of job interviews with the virtual agent playing the role of the recruiter. The evaluation of our approach is based on a comparison of the socially adaptive agent to a simple scripted agent and to an emotionally-reactive one. Videos of these three different agents in situation have been created and evaluated by 83 participants. This subjective evaluation shows that the simulation and expression of social attitude is perceived by the users and impacts on the evaluation of the agent’s credibility. We also found that while the emotion expression of the virtual agent has an immediate impact on the user’s experience, the impact of the virtual agent’s attitude expression’s impact is stronger after a few speaking turns.