Four cases of acquired hemophilia A following immunization with mRNA BNT162b2 SARS-CoV-2 vaccine

Acquired hemophilia A (AHA) is a rare autoimmune disease caused by neutralizing autoantibodies against coagulation Factor VIII. Immunomodulatory effects of SARS-CoV-2 vaccination are still poorly understood, with reports of immune-mediated conditions developing after immunization. In the province of Reggio Emilia, Northern Italy, we observed four cases of AHA following SARS-CoV-2 immunization with mRNA BNT162b2 vaccine (produced by Pfizer-BioNTech) during the first eight months from the beginning of SARS-CoV-2 vaccination campaign. During this time frame, 235,597 people received at least one dose of BNT162b2 vaccine. The total population of Reggio Emilia province is 526,349. The unusual observation of four cases of AHA in our province could be of interest and could sensitize healthcare personnel toward a possible complication of SARS-Cov-2 immunization. Nonetheless, vaccination benefits exceed potential side effects and play a central role in individual and public health to effectively protect people from COVID-19 and to stop the pandemic.