This clinical trial is being conducted to learn more about a potential treatment (valoctocogene roxaparvovec) for people with severe hemophilia A. This research study will test and confirm the safety and effectiveness of the 6E13 vg/kg dose of the study drug (valoctocogene roxaparvovec) that contains the correct gene to make Factor VIII so that the body can make its own Factor VIII that functions properly. Only one dose of valoctocogene roxaparvovec is being given in this study, and this dose has been previously studied in another clinical trial in patients with hemophilia A. This is a phase 3 study which is meant to show that the study drug is safe and works to help treat hemophilia A. The study will see if liver cells are able to make Factor VIII that functions properly after receiving this study drug. The study will also examine the effects that the study drug has on how much Factor VIII concentrates patients have to inject into their veins and on their bleeding episodes after the study drug has been administered. Finally, the study will see if and how the body responds to the study drug - for example, whether liver cells become inflamed or whether the body makes antibodies (something the immune system makes to protect itself against things like bacteria and viruses) against the vector or the new Factor VIII gene.