This is a Phase 3, global, randomized, open-label, multicenter, trial evaluating brelovitug (BJT-778) vs bulevirtide for the treatment of chronic hepatitis delta infection (CHD). The main goal of this study is to test the effectiveness of brelovitug compared to bulevirtide as a long-term treatment in patients with chronic HDV infection.

Study consists of 2 arms. Approximately 172 participants will be randomized 3:1 to one of the following treatment arms:

Arm 1: Participants will receive brelovitug 300 mg subcutaneously once weekly for 96 weeks.

Arm 2: Participants will receive bulevirtide 2 mg subcutaneously once daily for 48 weeks, followed by brelovitug 300 mg subcutaneously once weekly for the next 48 weeks.

Key Inclusion Criteria:

1. Willing and able to provide written informed consent
2. Chronic HDV infection
3. HDV RNA >500 IU/mL at Screening
4. ALT >ULN at Screening
5. Willing to take or already taking HBV neucleos(t)ide therapy.

Key Exclusion Criteria:

1. Pregnant or nursing females
2. Unwilling to comply with contraception requirements during the study
3. Difficulty with blood collection and/or poor venous access for the purposes of phlebotomy
4. Clinical hepatic decompensation (i.e., ascites, encephalopathy variceal hemorrhage).
5. Solid organ or bone marrow transplantation
6. Presence of other liver disease(s) (non-HBV/HDV), such as nonalcoholic steatohepatitis (NASH), alcohol associated hepatitis, cholestatic liver disease, hepatocellular carcinoma.

Note - Other protocol-defined Inclusion/Exclusion criteria apply.