##1. Definition of Acquired Hemophilia A and new challenges after mRNA vaccine introduction Acquired hemophilia A (AHA) is an extremely rare autoimmune bleeding disorder caused by the development of autoantibodies against coagulation factor VIII. Historically it has been associated with cancer, infection, pregnancy, etc., but after the large‑scale rollout of the COVID‑19 mRNA vaccine (Tozinameran/Pfizer) cases of this disease have been reported, raising the need to elucidate a potential association between vaccination and AHA as a new public‑health task. In particular, the abrupt onset of bleeding symptoms in otherwise healthy adults demands a meticulous review of vaccine safety surveillance systems.

##2. Detailed analysis of 27 cases from the French Pharmacovigilance Database (FPVD) The French drug‑monitoring authority performed real‑time monitoring and analyzed 27 AHA cases that occurred after Tozinameran vaccination. The analysis showed that patients typically manifested symptoms within a median of 23 days after the second dose, with the most common presentation being spontaneous hematomas leading to severe anemia. Fifteen percent of patients experienced a fatal outcome, and despite thorough investigations, no alternative underlying cause for AHA was identified in the majority of cases, strongly suggesting a possible causal relationship with the vaccine.

##3. Symptom aggravation upon re‑exposure as decisive evidence for causality The most noteworthy observation in this dataset is the subset of patients whose symptoms worsened after a subsequent administration of the same mRNA vaccine. The recurrence of hemophilia manifestations following re‑vaccination provides decisive evidence that the immune system mounted a specific autoimmune response to a vaccine component. This indicates that the vaccine can act as a trigger for auto‑antibody production in individuals with a particular immunologic background, rather than representing a random coincidence.

##4. Need for advanced safety‑monitoring systems and precise preventive strategies The true value of this study lies in demonstrating the importance of a “real‑time surveillance system” for rare adverse events. It is essential to educate clinicians to promptly consider AHA when unexplained bleeding or bruising occurs after vaccination and to order coagulation factor assays without delay. Future efforts should use such data to identify high‑risk groups with a predisposition to autoimmune disease, allowing personalized vaccination plans that preserve both confidence in and safety of the vaccine.