This is a multicenter, open label, randomized Phase 3 clinical study to evaluate tobevibart + elebsiran in participants with Chronic HDV Infection not virologically suppressed with bulevirtide

Inclusion Criteria:

1. Male or female ages 18 to 70 years at screening
2. HDV RNA ≥ 500 IU/mL at screening
3. Receiving BLV 2 mg SC QD for ≥ 24 weeks at Day 1
4. Noncirrhotic or compensated cirrhotic liver disease at screening
5. On NRTI therapy against HBV for at least 12 weeks prior to day 1 or have HBV DNA < 10 IU/ml at screening, currently on locally approved NRTI therapy

Exclusion Criteria:

1. Serum ALT ≥ 5 × ULN
2. Any clinically significant chronic or acute medical or psychiatric condition that makes the participant unsuitable for participation.
3. History of significant liver disease from non-HBV or non-HDV etiology
4. History of allergic reactions, hypersensitivity, or intolerance to study drug, its metabolites, or excipients.
5. History of anaphylaxis
6. History of immune complex disease
7. History of autoimmune disorder
8. Current therapy or therapy within 24 weeks of screening with an immunomodulatory agent, immune checkpoint inhibitors, immunosuppressants, cytotoxic or chemotherapeutic agent, or chronic systemic corticosteroids.