FDA Approves Hibsago: A New Chronic Hepatitis B Treatment Aims for a “Functional Cure”
The FDA has approved Hibsago (bepirovirsen), a new chronic hepatitis B treatment from GSK and Ionis Pharmaceuticals. It is the first antisense medicine for the disease. In two Phase 3 trials, about one in five eligible patients reached a “functional cure”: the virus stayed suppressed six months after they stopped all hepatitis B medicine.
The U.S. Food and Drug Administration announced the approval on October 20, 2026. Hibsago is the first FDA-approved antisense oligonucleotide for chronic hepatitis B. Today’s standard pills keep the virus in check but usually have to be taken for years, often for life. Hibsago is a six-month course added to that therapy, and its goal is to let some patients stop treatment altogether. Below we explain how it works, who qualifies, what the trials showed, and the safety warnings that come with it.
At a Glance: The Hibsago Approval
| Item | Detail |
|---|---|
| Drug | Hibsago (bepirovirsen), subcutaneous injection |
| Companies | GSK plc (LSE/NYSE: GSK); developed with Ionis Pharmaceuticals (NASDAQ: IONS) |
| Approved | October 20, 2026 (FDA); also approved in Japan |
| Drug class | Antisense oligonucleotide (ASO), the first approved for hepatitis B |
| Treatment length | Up to 24 weeks, given alongside existing antiviral pills |
| FDA designations | Fast Track, Breakthrough Therapy, Priority Review |
| Safety label | Boxed warning for serious liver reactions and low platelet counts |
How the New Chronic Hepatitis B Treatment Works
Hepatitis B virus (HBV) infects liver cells. In chronic infection, it leaves behind a durable genetic template that keeps producing viral proteins. The most important of these is the hepatitis B surface antigen (HBsAg). Current antivirals, known as nucleos(t)ide analogues (for example entecavir and tenofovir), block the virus from copying its DNA. They do little to stop HBsAg production, and HBsAg is thought to help the virus dodge the immune system. That is one reason relapse is common when people stop the pills.
Bepirovirsen takes a different approach. An antisense oligonucleotide is a short, synthetic strand of genetic material built to bind specific RNA messages. According to the FDA, Hibsago targets the genetic instructions the virus uses to copy itself and make its proteins. That lowers both the amount of virus and the amount of HBsAg in the body. The aim is a “functional cure”: the virus stays undetectable and HBsAg disappears from the blood even after all treatment stops. Functional cure is not the same as eradication, because traces of viral DNA can remain in liver cells.
Who Is Eligible
The FDA approved Hibsago for use together with existing antiviral therapy in adults with chronic HBV infection who:
- do not have cirrhosis;
- have taken HBV antiviral therapy for at least six months;
- have suppressed HBV levels in the blood; and
- have an HBsAg level of 3,000 IU/mL or lower, measured with an FDA-authorized test.
Alongside the drug, the FDA authorized a companion diagnostic, the Roche Elecsys HBsAg II quant II RxDx assay, to select patients and monitor them during treatment. The companies’ prescribing information says Hibsago is not recommended for people with hepatitis D coinfection. Safety and effectiveness have not been established in people under 18.
The Evidence: B-Well 1 and B-Well 2 Phase 3 Results
Verified facts (FDA)
The FDA reviewed two placebo-controlled trials. In its announcement, the agency reported that:
- 24% of patients given Hibsago met the criteria to stop their existing HBV medicine. No placebo patients did.
- 19% of patients given Hibsago still had the virus controlled, with HBsAg undetectable in the blood, 24 weeks after stopping all HBV treatment.
Company-reported trial data (GSK/Ionis)
In their October 20 approval release, the companies said that B-Well 1 (NCT05630807) and B-Well 2 (NCT05630820) were global, randomized, double-blind trials run in 29 countries. Both met their primary endpoint. The pooled figures they reported:
| Group (baseline HBsAg) | Hibsago: functional cure | Placebo: functional cure |
|---|---|---|
| ≤3,000 IU/mL (primary population) | 233 of 1,220 (19%) | 0 of 614 (0%) |
| ≤1,000 IU/mL (key secondary) | 200 of 768 (26%) | 0 of 393 (0%) |
Source: GSK/Ionis company statement. Functional cure was defined as HBV DNA and HBsAg both undetectable for at least 24 weeks after stopping all treatment.
The companies also said that, in their estimate, standard antiviral therapy alone usually produces functional cure in fewer than 1% of patients per year. Headline Phase 3 results were first announced in May 2026.
What the numbers mean
Analysis: A cure rate near 20% means most treated patients will not reach functional cure and will keep taking antiviral pills. Still, the trials compared Hibsago against a placebo group in which nobody reached the endpoint. The results also suggest people who start with lower HBsAg levels do better. That pattern is why patients are selected with an HBsAg test.
Safety: A Boxed Warning and Close Monitoring
The FDA label includes a boxed warning, the agency’s most serious, for two risks:
- Serious liver reactions. The companies describe on-treatment liver “flares” with sharp rises in the liver enzyme ALT, mostly within the first 12 weeks.
- Low platelet counts (thrombocytopenia). These can raise the risk of potentially life-threatening bleeding. The prescribing information calls for platelet checks at least weekly.
Other warnings include worsening kidney function, serious inflammatory reactions such as vasculitis, and serious risks if the injection is not given correctly. According to the FDA, the most common side effects were injection-site reactions, fever, fatigue, and headache. Patients need regular blood tests before and during treatment, plus monitoring after they stop antivirals in case the hepatitis returns.
Who Could Benefit
According to GSK and Ionis, about 1.7 million people in the U.S. and more than 240 million worldwide live with chronic hepatitis B. The World Health Organization lists hepatitis B as a leading cause of liver cirrhosis and liver cancer. For the patients who qualify, a fixed six-month course that could end daily medication would be a significant change.
What Officials, Companies, and Experts Are Saying
- FDA: Wendy Carter, DO, Acting Director of the Office of Infectious Diseases in the FDA’s Center for Drug Evaluation and Research, said Hibsago “provides a new treatment approach that gives some patients the possibility of maintaining control of the virus” after chronic HBV treatment ends.
- Company statement: Ionis CEO Brett P. Monia, Ph.D., said, “We believe Hibsago will bring new hope to people living with chronic hepatitis B.”
- Expert commentary (in the company release): Norah Terrault, MD, MPH, Chief of Gastroenterology & Hepatology at USC Keck Medicine, called it “the start of a new era in treating people living with CHB.”
Next Steps
- Launch and access: GSK will commercialize Hibsago in the U.S. The release says some doses may be given at home after the first one. Pricing and insurance coverage were not detailed in the materials we reviewed.
- Global filings: GSK says more regulatory decisions are expected “in the coming months.” Bepirovirsen has Breakthrough Therapy and Priority Review designations in China.
- Economics for Ionis: GSK licensed bepirovirsen from Ionis in 2019. Ionis is eligible for further milestones and tiered royalties of 10–12% on net sales, according to the company.
- Open questions (developing): how long functional cures last beyond the trial follow-up, how the drug performs in routine practice given its monitoring requirements, and whether combining it with other investigational therapies could raise cure rates.
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Sources
- FDA: FDA Approves First-of-Its-Kind Chronic Hepatitis B Treatment (Oct. 20, 2026)
- Ionis/GSK approval press release (via BioSpace)
- Ionis/GSK Phase 3 headline results (May 2026, Business Wire)
- ClinicalTrials.gov: B-Well 1 (NCT05630807) and B-Well 2 (NCT05630820)
- World Health Organization: Hepatitis B fact sheet
This article is for general information and is not medical advice. People with hepatitis B should talk with their healthcare provider about whether any treatment is right for them.
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