Objectives - To describe French people’s beliefs regarding how the flu is transmitted and to analyze their relationship with seasonal flu vaccination. Methods - A subsample of 4,749 individuals (aged 15–79) answered questions about the flu during the 2010 Health Barometer survey. The responses were analyzed using ascending hierarchical clustering and logistic regression. Results - The beliefs observed are generally accurate but also socially differentiated, with those deviating from preventive messages being more common among individuals of lower socioeconomic status. Those who attribute transmission to all possible modes are less likely to get vaccinated against seasonal influenza. Conclusions - The beliefs studied here influence vaccination behaviors, but those that are “false” may nonetheless be consistent, and thus difficult to change. These beliefs also reveal social inequalities that must be taken into account by prevention efforts. [author’s abstract]