Background Healthcare workers (HCW) are a priority group for COVID-19 vaccination. The start of the COVID-19 campaign among French HCW offered an opportunity to explore the psychological antecedents of vaccine hesitancy (VH), in particular their extension from the 5C model (complacency, confidence, convenience, calculation, collective benefit) to a 7C model including social conformism and confidence in the system. Methods We developed a knowledge and attitude (KA) questionnaire with 30 items relating to the 7 components of psychological antecedents. The questionnaire was administered online among a snowballing sample of French HCW, recruited December 2020 through January 2021 via professional organizations. We used multivariate logistic regression to explore the association of 7C components and individual KA items with COVID-19 vaccine intention. Results Among the 5234 participants, the vaccine intention model fits (pseudo R-squared values (R2)) of individual components ranged from R2=0.48 for Calculation to R2=0.07 for Convenience, with R2=0.29 for Confidence in System and R2=0.26 for Social Conformism. In nested models including the initial 5C components, adding Confidence in System or Social Conformism increased the model fit significantly. In a multivariate model including a shortlist of items, the strongest associations with vaccine intention were observed for a positive attitude on the vaccine’s benefit-risk balance (strongly agree vs. strongly disagree: odds ratio 16.81, 95%-confidence interval 9.66-29.25). Discussion The results suggest that social conformism and confidence in the system are essential independent antecedents of VH. This questionnaire can be used to explore COVID-19 VH accompanying the transition into a long-term vaccination strategy.