Evolution of the industrialized society had led to a risk management policy in many domains. Assessment of health care risk in the case of infectious diseases often includes mathematical models. Results of modelling were used in France to design emergency plans against flu pandemic. We believe that models cannot predict the features of the future outbreaks because the intrinsic properties of an emergent pathogen and the ecosystem in which it is developing are very complex. Of course, prediction of future outbreaks is not possible without using models, but we think that it is an illusion to presently believe that an emerging phenomenon can be anticipated by using only prediction from models. The recent pandemic caused by the novel A/H1N1 virus has confirmed the unpredictability of infectious diseases. The rapid evolution in several domains such as antimicrobial therapeutics, vaccine and hygiene conditions make comparison with past pandemics hard. The adherence of populations to prevention measures and immunisation campaigns are unpredictable. In addition, the presentation of pessimistic models is deleterious. They impress governments and provoke fears. There is a striking necessity to develop the number and the capacities of sentinel centres to take and adapt decisions based on timely available scientific information.