A late-stage trial for chronic hepatitis delta has shown promising results for a combination therapy developed by Vir Biotechnology. The drug pairing of elebsiran and tobevibart met its primary endpoint in the ECLIPSE 1 phase 3 study, with 44% of treated patients achieving undetectable hepatitis delta virus (HDV) RNA levels alongside normalized liver enzyme levels by week 48. By comparison, no patients in the delayed-treatment cohort reached this target at week 12, and the difference carried statistical significance with a P value of less than .0001.
Researchers presented these findings during an oral session at The Liver Meeting 2026 in Denver, Colorado, hosted by the American Association for the Study of Liver Diseases. The trial included 124 adults with chronic hepatitis delta, with 83 assigned to immediate treatment and 41 placed in a delayed-treatment group that began therapy at week 12. The primary goal required both undetectable HDV RNA and normalized alanine aminotransferase (ALT) levels.
Additional data revealed that 79% of treated patients showed undetectable HDV RNA alone, while none in the delayed group did. Liver enzyme normalization occurred in 53% of treated patients versus just 5% in the control group. Among those with cirrhosis, 46 participants in total, 85% achieved undetectable HDV RNA, whereas 73% of the 37 patients without cirrhosis met the same benchmark. An exploratory analysis further showed that 95% of treated patients had hepatitis B surface antigen levels below 10 IU/mL, compared to 0% in the delayed-treatment group.
Vir Biotechnology is now preparing a global regulatory submission for the combination, which already holds Breakthrough Therapy and Fast Track designations from the FDA. The company completed patient enrollment in November 2025 and anticipates results from two additional phase 3 trials, ECLIPSE 2 and ECLIPSE 3, in the first quarter of 2027. A full regulatory filing with the FDA is planned for mid-2027. In Europe, the therapy has received EMA PRIME and orphan drug designations.
Safety data from ECLIPSE 1 identified one grade 3 adverse event, a temporary drop in neutrophil count that resolved within 15 days. No participants discontinued treatment due to side effects. Most adverse events were mild to moderate and transient, with flu-like symptoms being the most common and typically resolving within 24 to 48 hours.