This study will seek to determine the safety, kinetics and efficacy of a single IV infusion of ZS801.~The dose level is 5.0×10^12vg/kg; Dose addition may occur based on the safety and FIX activity on steady state.~Subjects will provide informed consent and then undergo screening assessments up to 6 weeks prior administration of ZS801. All subjects will undergo 52 weeks safety and efficacy observation. Then subjects
A non-randomized, open-label study to evaluate the safety, kinetics and efficacy of a single intravenous infusion of ZS801 in hemophilia B subjects with endogenous FIX ≤2%.