Hepatitis B's First Functional Cure Reaches the US Market
GSK's Hibsago won FDA approval as the first functional-cure option for chronic hepatitis B, but only about one in five eligible patients achieved durable control, and the label carries a boxed warning.
The US Food and Drug Administration has approved GSK plc's Hibsago, known generically as bepirovirsen, as the first treatment that can produce a functional cure for chronic hepatitis B. The medicine is also the first FDA-approved antisense oligonucleotide for the disease. It is given with existing nucleos(t)ide analogue antiviral therapy, not in place of it.
Eligibility is tight. The approval covers adults without cirrhosis who have been on hepatitis B antiviral therapy for at least six months, have suppressed HBV levels, and have HBsAg of 3,000 IU/mL or less. The FDA also authorized a Roche Elecsys HBsAg II quant II RxDx assay as a companion diagnostic to select and monitor those patients.
That mix of a real functional-cure option and a narrow gate is the story. In the pivotal B-Well trials, 19% of treated patients achieved durable viral control. Current standard-of-care antiviral therapy alone typically produces a functional cure in less than 1% of patients after one year.
What the B-Well trials showed
GSK ran B-Well 1 and B-Well 2 as randomized, double-blind, placebo-controlled studies across 29 countries. Among 1,220 patients who received bepirovirsen, 233, or 19%, met the functional-cure definition, compared with 0 of 614 on placebo. Functional cure means HBV DNA and HBsAg remain undetectable for at least 24 weeks after all treatment is stopped, so the immune system is controlling the virus without medication.
A key secondary endpoint tightened the picture. Patients with HBsAg of 1,000 IU/mL or less, a group that represents about 45% of diagnosed chronic hepatitis B cases globally, posted a 26% functional cure rate (200 of 768 versus 0 of 393 on placebo).
The FDA separately reported that 24% of patients who received bepirovirsen met the requirements to stop their existing medicine, versus none on placebo, and that 24 weeks later 19% still had the virus under control with HBsAg undetectable.
A six-month course and a boxed warning
Hibsago is injected under the skin for up to 24 weeks, a six-month course, alongside existing antiviral medicine. That antiviral continues for at least 24 weeks after the last injection. Some patients may then stop all treatment. There is an option of self-administration after the first dose.
The label carries real toxicity flags. Hibsago has a boxed warning for serious liver reactions and low platelet counts, which raise bleeding risk. It also has warnings for worsening kidney function and serious inflammatory reactions such as vasculitis. The FDA granted Priority Review, Fast Track, and Breakthrough Therapy designations.
GSK Chief Scientific Officer Tony Wood said, "For the first time, with Hibsago, US patients have the potential to achieve functional cure after a six-month treatment course."
Ionis royalties and a wider filing queue
Chronic hepatitis B affects approximately 1.7 million people in the United States and more than 240 million people worldwide, and causes around 1.1 million deaths per year, according to figures GSK cites from the WHO Global Hepatitis Report 2026. Hepatitis B is the leading cause of liver cancer globally. Chronic infection accounts for roughly 56% of all global liver cancer cases.
Bepirovirsen was licensed by GSK from Ionis Pharmaceuticals in 2019, and Ionis collaborated on development. Under that agreement Ionis receives tiered royalties of 10-12% on net sales plus additional milestone payments. The drug is already approved in Japan. GSK says additional regulatory submissions are advancing, with key decisions anticipated in coming months.
A gated first step
Hibsago puts GSK (LSE/NYSE: GSK) in the first-mover position in the antisense oligonucleotide race for a hepatitis B functional cure. The clinical result is measurable: a 19% durable functional cure rate in the overall labeled population, against a typical rate below 1% on antivirals alone after a year, and a 26% rate in the lower-antigen subgroup.
The opportunity is still bounded by the label. Eligible patients are already on treatment, virologically suppressed, at or below an HBsAg cutoff, and free of cirrhosis. A companion diagnostic is required. A boxed warning flags serious liver reactions and low platelets. Patients who meet those conditions can take a six-month injection course and, in some cases, stop every medicine afterward. The first functional-cure option for chronic hepatitis B is now on the US market as that gated, six-month add-on.
