Fidanacogene elaparvovec-dzkt (Beqvez; Pfizer Inc.) is a single-infusion gene therapy for the treatment of adults with moderate to severe hemophilia B who currently use factor IX prophylaxis therapy, or have current or historical life-threatening hemorrhage, or have repeated, serious spontaneous bleeding episodes, and do not have neutralizing antibodies to adeno-associated virus serotype Rh74var capsid as detected by a U.S. Food and Drug Administration-approved test.