Résumé
Aim/Objective: This study aimed to characterize nocebo responses and their associated factors following COVID-19 vaccination. Methods: We conducted a case-control study using pharmacovigilance records from a regional pharmacovigilance centre in France, supplemented by a cross-sectional self-administered questionnaire study. Patients reporting allergy-like symptoms without fever and without a diagnosis of anaphylaxis were considered nocebo cases. Controls reported reactogenic or localised reactions. Data on demographics, medical history, vaccinations and psychological factors were collected and analysed using multivariate logistic regression to identify risk factors associated with nocebo effects. Results: We included 1038 patients: 320 nocebo cases (mean age 49.7 [SD: 16.2], 75.3% female) and 718 controls (mean age 48.5 [SD: 15.1], 75.3% female). Allergy-like symptoms in cases were predominantly cutaneous (71.8%) and respiratory (38.8%), occurring immediately in 38.1% and after the first dose in 43.4%. In multivariate analysis, nocebo responses were positively associated with age (OR 1.01, 95% CI: 1-1.02, p = 0.13), history of allergy (OR 1.62, 95% CI: 1.22-2.16, p = 0. 001) and BNT162b2 mRNA vaccine (Comirnaty) (OR 1.60, 95% CI: 1.20-2.14, p = 0.001) and negatively correlated with the perceived vaccine effectiveness score (OR 0.92, 95% CI: 0.87-0.97, p = 0.002). Conclusion: This study suggests that the nocebo effect differs according to the type of vaccine and is more common in older people, those with a history of allergy, and those with a poorer perception of vaccine effectiveness. The influence of these clinical and psychological factors on the nocebo effect needs to be further confirmed in order to better understand this phenomenon.