A drug that lets patients stop treatment entirely

Chronic hepatitis B has always demanded a grim trade-off from patients: stay on antiviral medication indefinitely, often for the rest of your life, or risk the virus rebounding and eventually causing cirrhosis, liver cancer, or liver failure. Existing nucleoside and nucleotide antivirals like tenofovir and entecavir control the virus well, but they almost never eliminate it enough for patients to stop taking them safely. A new experimental drug from GSK just demonstrated it can break that cycle for a meaningful share of patients, and the results were significant enough that Medscape Medical News reported them under the headline that a functional cure for hepatitis B is now "achievable."

The drug, bepirovirsen, is an antisense oligonucleotide — a synthetic molecule engineered to bind to and block specific viral genetic sequences, in this case targeting hepatitis B virus transcripts directly. Phase 3 results from two replicate trials, called B-Well 1 and B-Well 2, were published in The New England Journal of Medicine, with the lead investigator, Dr. Jinlin Hou of Southern Medical University in Guangzhou, China, describing findings that represent what one independent commentator called a "landmark" moment for the field.

The numbers behind a one-in-five cure rate

The trial design itself was demanding by design. Researchers enrolled 1,834 adults with noncirrhotic chronic HBV infection across both studies, randomly assigning them in a 2-to-1 ratio to receive either weekly subcutaneous bepirovirsen injections or a placebo, alongside their existing antiviral therapy, for 24 weeks. Patients who met specific criteria — undetectable HBV DNA and hepatitis B surface antigen, known as HBsAg, sustained from week 24 through week 46 — were then allowed to discontinue all conventional antiviral treatment at week 48, with researchers tracking outcomes through week 72 to see whether the virus stayed suppressed without ongoing medication.

The results were consistent across both trials. In B-Well 1, 127 of 650 patients receiving bepirovirsen, or 20%, achieved what researchers defined as a functional cure at week 72 — meaning undetectable HBV DNA and HBsAg with no need for rescue therapy — compared to zero of 328 patients in the placebo group. B-Well 2 produced nearly identical results: 106 of 570 patients, or 19%, achieved functional cure versus zero of 286 placebo recipients. Not a single patient in either placebo arm achieved the outcome, which is what makes the bepirovirsen results statistically unambiguous rather than a marginal improvement open to interpretation.

What "functional cure" actually means, and what it doesn't

It's worth being precise about the terminology here, because "cure" can mean different things depending on the disease. Dr. Joseph K. Lim, a professor of medicine and director of clinical hepatology at Yale School of Medicine, who wasn't involved in the trials, praised the results as "unequivocally groundbreaking" while cautioning that this represents a functional cure rather than a sterilizing one. A functional cure means the virus is suppressed to undetectable levels and the patient can safely stop treatment — it does not mean every trace of the virus has been eliminated from the body's cells, since hepatitis B can persist in a dormant form even when surface antigen and viral DNA drop below detection thresholds.

That distinction matters practically because it shapes what patients should expect. A functional cure dramatically lowers the risk of the disease's worst long-term outcomes — cirrhosis, liver cancer, liver-related death — and frees patients from a lifetime of daily medication. But it isn't necessarily permanent immunity from ever needing treatment again, and long-term monitoring beyond the 72-week trial window will be needed to confirm how durable these outcomes actually are.

The safety trade-off patients will need to weigh

No effective drug arrives without costs, and bepirovirsen's side-effect profile is a real part of this story. In a pooled analysis at 72 weeks, adverse events occurred in 91% of patients receiving bepirovirsen compared to 73% of those on placebo, according to results reported by CIDRAP, the Center for Infectious Disease Research and Policy. Serious adverse events were less common but still elevated: 7% in the bepirovirsen groups versus 4% in placebo groups. During the active treatment period specifically, grade 3 or higher adverse events — considered severe or medically significant, though not immediately life-threatening — occurred in 16% of bepirovirsen recipients compared to just 3% of placebo patients, with elevated liver enzyme levels, specifically ALT, being the most common serious side effect, affecting 6% of treated patients.

Treatment discontinuation due to adverse events occurred in 3% of the bepirovirsen group. That's a meaningful number in absolute terms, though it needs to be weighed against a treatment that offers a real chance of freedom from lifelong daily medication — a trade-off patients and their doctors will need to navigate individually rather than treat as settled by the topline cure rate alone.

Where the drug goes from here, and who stands to benefit most

Bepirovirsen is currently under priority review by the U.S. Food and Drug Administration, holding both Breakthrough Therapy and Fast Track designations, according to GSK's own announcement of the results. The drug is simultaneously under review by regulators in Europe, Japan — where it holds SENKU designation — and China, where it has received Breakthrough Therapy and Priority Review status. GSK has said it anticipates first regulatory decisions arriving in the third quarter of 2026, and the company entered a strategic collaboration with Sino Biopharmaceutical in May 2026 specifically aimed at accelerating patient access in China at launch.

One detail from the trial data deserves particular attention for how this drug will eventually be used in clinics: functional cure rates were higher among patients who started treatment with lower baseline HBsAg levels, according to reporting from aidsmap. That suggests bepirovirsen isn't likely to become a universal one-size-fits-all replacement for existing antivirals, but rather a targeted option best suited to patients whose viral markers are already trending toward control. Dr. Seng Gee Lim of Singapore's National University Health System, another independent researcher who reviewed the data, called the phase 3 results "a major step forward in the search for a finite treatment for chronic hepatitis B" — a description that captures both the genuine significance of a 20% cure rate in a disease that has resisted finite treatment for decades, and the reality that four out of five patients in these trials still didn't achieve that outcome.

*This article was researched using publicly available reporting from The New England Journal of Medicine, GSK, Medscape Medical News, CIDRAP, aidsmap, AJMC, and Cancer Health's coverage of the B-Well 1 and B-Well 2 phase 3 clinical trials. It is intended for informational purposes and is not medical advice.*