Three and a half years after U.S. approval, Canada on May 20, 2026, treated its first patient with Hemgenix. With a list price of 3.5 million dollars, the drug is considered the world's most expensive. For hemophilia B patients who otherwise inject clotting factor multiple times weekly for decades, a single infusion should suffice.
What Is Hemophilia B?
Hemophilia B is an inherited bleeding disorder affecting almost exclusively males. Patients produce too little or no functional factor IX protein, essential for blood clotting. Without treatment, even mild bruising can trigger internal bleeding that permanently damages joints or becomes life-threatening. Roughly 42,000 people with hemophilia B are estimated worldwide.
Standard therapy is cumbersome: severely affected patients inject factor IX two to three times weekly, meaning 104 to 156 infusions annually. Modern prolonged-half-life preparations reduce this to approximately 52 annual injections. In the U.S., such prophylaxis costs an average 700,000 to 800,000 dollars yearly; lifetime costs exceed 20 million dollars.
How Hemgenix Works
Hemgenix targets the cause, not symptoms. The active ingredient etranacogene dezaparvovec uses a harmless adeno-associated virus type 5 (AAV5) as a transport vehicle. It delivers an optimized FIX gene copy directly into patient liver cells. Liver cells then produce factor IX themselves, in a variant CSL Behring states is five to eight times more active than natural protein.
On November 22, 2022, the FDA approved Hemgenix as the world's first hemophilia B gene therapy. CSL Behring and biotech company uniQure jointly developed the drug. The list price totals 3.5 million dollars, making Hemgenix the world's most expensive medication at approval.
What the HOPE-B Trial Shows
The approval trial HOPE-B has documented efficacy over five years. Long-term data published in the New England Journal of Medicine are unequivocal: four years after single infusion, 94 percent of study participants were free from any prophylactic ongoing treatment. Blood factor IX activity averaged 36.1 percent of normal, a level sufficient for most patients to prevent spontaneous bleeding. Bleeding rate dropped roughly 65 percent versus prior standard therapy.
Over five years, study authors reported no serious long-term side effects. Early theoretical concern about liver cancer from the viral vector was not confirmed by five-year data.
Other Gene Therapies as Comparison
Hemgenix is not the first step in this direction, but the most far-reaching approved. In December 2023, FDA approved Casgevy, a CRISPR-based therapy for sickle cell disease, another inherited blood disorder. For hemophilia A, the more common sister disease, BioMarin deployed Roctavian gene therapy in multiple markets. Approved gene therapies for inherited diseases have significantly increased in the past three years.
Another comparison point: hepatitis C cure. Since 2014, directly-acting antivirals cure the disease in over 95 percent of cases. Previously, chronic hepatitis C was deemed incurable. Hemgenix could mean a similar turning point for hemophilia B, with the difference that antiviral hepatitis drug prices fell rapidly post-launch, while structural features of gene therapies—complex manufacturing and small patient populations—tend to sustain high costs.
Who Pays 3.5 Million Dollars?
Price is the critical bottleneck. In the U.S., many major health insurers have included Hemgenix in their reimbursement lists, some with outcome-based agreements: if the therapy doesn't achieve promised bleeding rates, the insurer receives partial refund. CSL Behring argues that therapy saves up to 20 million dollars lifetime in treatment costs, economically justifying the 3.5 million list price.
Scientists note the equation doesn't work for health systems in low- and middle-income countries. There, even conventional factor IX prophylaxis is often inaccessible. Therapy costing more per treatment than many nations spend annually on entire medication supply structurally deepens existing inequalities.
Three Conditions for Broad Availability
How quickly hemophilia B patients elsewhere benefit depends on three factors. First, national regulators must approve the drug, still pending or under review in Europe and elsewhere. Second, insurance systems must develop reimbursement models accommodating a single payment of this magnitude. Third, patients need access to specialized centers for safe infusion.
How slowly this process moves is shown by the U.S.: despite Hemgenix approval since November 2022, only roughly 135 patients worldwide had received such therapy by mid-2024. For 42,000 hemophilia B patients globally, approval is a breakthrough. Broad market access is not yet.