Hepatitis Delta Phase 3 Results: Vir’s Elebsiran and Tobevibart Meet Primary Goal in ECLIPSE 1
Vir Biotechnology (NASDAQ: VIR) says its two-drug combination for chronic hepatitis delta met the main goal of a pivotal Phase 3 trial. In the ECLIPSE 1 study, 44% of patients who got monthly elebsiran plus tobevibart had no detectable virus and normal liver enzymes at week 48. None of the patients in the delayed-treatment group did. The hepatitis delta Phase 3 results were presented on November 8, 2026, as a late-breaker at The Liver Meeting, the American Association for the Study of Liver Diseases (AASLD) annual meeting in Denver. Here is what the data show, why the disease matters, and what comes next.
Key Takeaways
- Primary endpoint met (company-reported): 44% vs. 0% reached undetectable HDV RNA plus ALT normalization (P < .0001).
- Virus undetectable: 79% of treated patients vs. 0% in the delayed arm.
- Safety: Most treatment-related side effects were mild to moderate and short-lived. Vir reported no treatment interruptions or discontinuations.
- Next steps: Two more Phase 3 readouts (ECLIPSE 2 and 3) are expected in Q1 2027, and Vir plans a U.S. regulatory filing in mid-2027.
What Is Hepatitis Delta?
Hepatitis delta virus (HDV) is an incomplete virus. It can only infect people who already have hepatitis B, because it uses the hepatitis B surface antigen (HBsAg) to build its own viral particles. The World Health Organization estimates that HDV affects about 5% of people living with chronic hepatitis B, or roughly 12 million people worldwide, as reported by HCPLive.
Chronic hepatitis delta is considered the most severe form of viral hepatitis. Co-infection speeds progression to serious liver disease in 70% to 90% of cases. In June 2025, the International Agency for Research on Cancer classified HDV as a Group 1 carcinogen, citing sufficient evidence that it causes liver cancer (hepatocellular carcinoma).
Treatment options are limited. In May 2026, the FDA granted accelerated approval to Gilead’s bulevirtide (Hepcludex), a once-daily injection that blocks the virus from entering liver cells. It is the first U.S. treatment for chronic HDV.
How the Elebsiran and Tobevibart Combination Works
Vir’s regimen pairs two drugs with complementary mechanisms, according to the company:
- Elebsiran is a small interfering RNA (siRNA). It is designed to silence hepatitis B genetic instructions in liver cells so they make less HBsAg, the protein HDV depends on.
- Tobevibart is a broadly neutralizing monoclonal antibody that targets HBsAg. It is designed to block the virus from entering liver cells and help clear viral particles from the blood.
In plain terms, one drug cuts off the supply of the protein the virus needs, and the other mops up what is already circulating. In ECLIPSE 1, patients received elebsiran 200 mg and tobevibart 300 mg as two subcutaneous injections every four weeks.
ECLIPSE 1 Trial Design
ECLIPSE 1 (NCT06903338) is a randomized, open-label Phase 3 trial. According to HCPLive:
- 124 adults were enrolled at 39 sites in 10 countries.
- Patients were randomized 2:1 to immediate treatment (83 patients) or delayed treatment starting at week 12 (41 patients).
- Participants had either no cirrhosis or compensated cirrhosis. About 55% had compensated cirrhosis. All were on nucleos(t)ide therapy for hepatitis B.
- The primary endpoint combined two measures: HDV RNA “target not detected” plus normal ALT (a liver-injury marker). It was measured at week 48 in the treatment arm and week 12 in the delayed arm.
The comparison group received no active treatment for the first 12 weeks. It was not a placebo or an active drug comparison.
Hepatitis Delta Phase 3 Results: The Numbers
The following figures are company-reported topline data from Vir’s November 8 release and AASLD presentation, as reported by HCPLive and Contagion Live. They have not yet appeared in a peer-reviewed journal.
| Measure | Immediate treatment (wk 48) | Delayed treatment (wk 12) |
|---|---|---|
| Undetectable HDV RNA + ALT normalization (primary) | 44% | 0% |
| Undetectable HDV RNA (key secondary) | 79% | 0% |
| Virologic response (undetectable or ≥2 log10 drop) | 100% | 0% |
| ALT normalization | 53% | 5% |
| HBsAg below 10 IU/mL (exploratory) | 95% | 0% |
The virus became undetectable in 85% of treated patients with compensated cirrhosis and 73% of those without cirrhosis.
Safety
Vir reported that most treatment-related adverse events were mild to moderate and transient. The most common was flu-like symptoms, mainly after the first dose, which usually resolved within 48 hours. One patient had a grade 3 event (a drop in neutrophil count) that resolved within 15 days. There were no treatment interruptions or discontinuations.
What the Evidence Does and Does Not Show
Verified facts: The trial is registered as NCT06903338. The data were presented as a late-breaking abstract at The Liver Meeting 2026. Bulevirtide holds U.S. accelerated approval.
Scientific evidence: The comparison is large (44% vs. 0%). But the trial is open-label, relatively small, and compares against a short no-treatment period rather than an active drug. A delayed-treatment arm shows that the drugs do something compared with nothing. It cannot show whether they beat existing therapy. HCPLive cautioned against cross-trial comparisons with bulevirtide. In bulevirtide’s separate MYR301 trial, 20% of patients had undetectable HDV RNA at week 48.
Supporting data: In the earlier Phase 2 SOLSTICE study, published in the New England Journal of Medicine in 2026, 66% of patients had undetectable HDV RNA at week 48, according to HCPLive.
What Researchers, the Company and Analysts Say
Investigator commentary: Nancy Reau, MD, of Rush University Medical Center, who presented the results, said in a statement: “For people living with CHD, the goal is not simply to reduce the amount of virus, but to drive it to levels where it is no longer detectable.”
Company statement: Vir CEO Marianne De Backer said: “Our ambition in hepatitis delta has always been to fundamentally change what patients can expect from treatment.”
Analyst commentary: Evercore ISI analyst Cory Kasimov wrote in a note to clients, as reported by BioPharma Dive, that “cross-trial caveats apply, but the gap is wide.” BioPharma Dive reported that Vir shares rose about 12% in early trading on November 9.
Who Could Benefit?
If approved, the combination could offer a monthly option for adults with chronic hepatitis delta, including those with compensated cirrhosis, who face a high risk of liver failure and cancer. A monthly injection could be easier for some patients than a daily one, but that has not been tested directly.
Next Steps and Regulatory Path
- Designations: The combination has FDA Breakthrough Therapy and Fast Track designations. Contagion Live reports it also holds EMA PRIME and orphan designations.
- ECLIPSE 2 (NCT07128550) is testing a switch to the combination in patients whose virus was not suppressed on bulevirtide.
- ECLIPSE 3 (NCT07142811) is a head-to-head comparison against bulevirtide in patients who have not taken it before. Both readouts are expected in Q1 2027.
- Filing: Vir plans to submit a U.S. regulatory package in mid-2027. Norgine holds the license for Europe, Australia and New Zealand.
- Competition (developing): Mirum Pharmaceuticals reported a successful Phase 3 trial (AZURE-1) of its HDV antibody brelovitug in September 2026, according to BioPharma Dive.
ECLIPSE 3 will matter most. It is the trial that can show whether the combination works better than the current standard.
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Sources
- HCPLive — Elebsiran Plus Tobevibart Suppresses HDV RNA in Phase 3 ECLIPSE 1 Trial (Nov. 8, 2026)
- Contagion Live — Elebsiran and Tobevibart Meet Primary End Point in Hepatitis Delta Study (Nov. 9, 2026)
- BioPharma Dive — Vir chronic hepatitis D drug results (Nov. 9, 2026)
- Vir Biotechnology — AASLD 2026 ECLIPSE 1 Oral Presentation (PDF)
- ClinicalTrials.gov — NCT06903338 (ECLIPSE 1)
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