Hemophilia B Clinical Trials

• Considered legally an adult, as defined by country regulations.

• Has congenital hemophilia B with known severe or moderately severe FIX deficiency (less than or equal to \[\<=\] 2% of normal circulating FIX) for which the participant is on continuous routine FIX prophylaxis.

• Has 2 consecutive detectable AAV5 NAb titer results between Screening and Visit L-Final using a validated AAV5 NAb assay (based on central laboratory results).

• Has greater than (\>) 150 previous exposure days to FIX replacement therapy.

• Has been on stable FIX prophylaxis for at least 2 months before Screening.

• Has demonstrated capability to independently, accurately, and in a timely manner complete the eDiary during the Lead-in Period, as judged by the investigator.

• Acceptance to adhere to contraception guidelines.

• Able to provide informed consent after receipt of verbal and written information about the study.

• Investigator believes that the participant (or the participant's legally acceptable representative\[s\]) understands the nature, scope, and possible consequences of the study and is able to adhere to the study procedures.