TMPRSS2 and COVID-19: Notably, aprotinin, another Kunitz‐type inhibitor, reached phase III trials as a COVID‐19 therapy and demonstrated the ability to inhibit TMPRSS2 and exhibit antiviral activity in vitro.[71, 72, 73, 74] However, aprotinin, derived from bovine lung tissue, was temporarily withdrawn from the European market due to severe side effects, including immunogenicity, allergic reactions, and off‐target effects associated with its broad‐spectrum antiprotease activity.[75] These limitations emphasize the need for safer and more targeted alternatives.