EMA Recommends Approval of First Gene Therapy for Hemophilia B — Fidanacogene Elaparvovec
The AAV5-based adeno-associated viral vector therapy, providing long-term expression of clotting factor IX, demonstrated a 96% reduction in annualized bleeding rate in the pivotal BENEGENE-2 study with a follow-up period of over three years.
We are witnessing the moment when gene therapy has ceased to be an experiment and has become a commercial war between two pharmaceutical giants for a market that, within five years, will completely redefine hemophilia B. Fidanacogene elaparvovec is not just the second player after Hemgenix. It is Pfizer entering a territory where CSL Behring and uniQure have spent two years trying to set a price standard of $3.5 million per infusion. Now the market will split, and this is the main invisible storyline that science journalists miss: the war is not over patients, but over insurance budgets that are not ready to pay $3.5 million for each gene therapy twice.
The Essence: What Is Really Happening
The EMA has issued a recommendation for approval of fidanacogene elaparvovec — a gene therapy based on an AAV5 vector carrying a highly active variant of the factor IX gene. After a single infusion, patients with severe and moderately severe hemophilia B begin to produce factor IX on their own, rather than receiving it intravenously once a week or every two weeks. The headline figures — a 96% reduction in annualized bleeding rate — come from the BENEGENE-2 study, where 45 patients received a dose of 5e11 vg/kg. But this is not just a clinical triumph. It is the establishment of a new paradigm: hemophilia transitions from a chronic disease to a condition that can be eliminated with a single infusion.
Why is this important right now? Because Hemgenix (etranacogene dezaparvovec) from CSL Behring and uniQure was approved by the FDA in November 2022 and by the EMA in early 2023. For two years, it was a monopoly, except for the Canadian and US markets, where Pfizer had already launched Beqvez — the same drug under a different brand. Now the monopoly is crumbling. Two drugs with the same AAV5 vector, the same mechanism of action, and nearly identical pricing in the US ($3.5 million) will compete in Europe.
Timeline and Context
The path to May 2026 is paved with strategic patents and quiet deals. Back in December 2014, Pfizer licensed SPK-9001 from Spark Therapeutics, paying a small upfront fee and taking responsibility for Phase 3 and commercialization. At that time, no analyst would have predicted that it would take twelve years to reach European approval. But gene therapy is a marathon of regulatory hurdles, not a sprint.
2022. December. Pfizer announces achievement of the primary endpoint in BENEGENE-2: mean annualized bleeding rate of 1.3 vs. 4.43 in the standard therapy group, a 71% reduction, p<0.0001. Secondary endpoints are equally impressive: a 78% reduction in treated bleeding rate and a 92% reduction in annualized factor IX infusion rate.
2023. BENEGENE-2 data presented at the ASH congress. Particular attention is drawn to a small but critical group of 6 patients who initially responded to therapy but then returned to prophylactic factor IX administration. Time to return varied from 155 to 623 days. Researchers found no predictors — neither age (mean 28.3 years among those who returned), nor region, nor race, nor peak factor IX level after therapy predicted loss of response.
2024-2025. Hemgenix receives approvals and begins penetrating European markets. Norway, Switzerland, Germany, and the UK approve reimbursement. France and Denmark also include the drug in their state guarantee systems. Simultaneously, Pfizer receives approvals in the US and Canada under the brand Beqvez.
2026, April 17. The EMA issues a positive recommendation for Durveqtix — the European brand of fidanacogene elaparvovec. Full approval by the European Commission is expected within the next 8-12 weeks.
Who Wins and Who Loses
Pfizer wins — and it's not just about direct sales of Durveqtix. Pfizer gains leverage over European insurance systems, where Hemgenix has already done the heavy lifting in negotiations. CSL Behring spent two years convincing payers that $3.5 million per infusion is a reasonable price, given that lifelong prophylaxis with factor IX costs between $300,000 and $1 million annually. Now Pfizer can enter with a slightly lower price or a more favorable money-back guarantee for inefficacy — and capture market share without bearing the costs of being first.
CSL Behring/uniQure loses — but not critically. Their Hemgenix has five-year data from the HOPE-B study: mean factor IX level around 36% of normal, 94% of patients discontinued prophylaxis, annualized bleeding rate reduced by approximately 90%. Moreover, Hemgenix has shown efficacy even in patients with pre-existing neutralizing antibodies to AAV5 — a competitive advantage that Durveqtix does not explicitly have.
Unexpected loser — manufacturers of standard clotting factors. The market for recombinant factor IX for hemophilia B prophylaxis is estimated at $3-4 billion annually. When two players enter the market offering a cure with a single infusion, this market begins to shrink. Patients who receive gene therapy no longer purchase factor IX weekly. Within 5-7 years, annual sales of factor IX could decline by 40-60%.
What the Media Isn't Saying
Here is a non-obvious insight that is hardly discussed: the problem of immune-mediated hepatotoxicity, which has emerged with the competitor, also poses risks for fidanacogene elaparvovec. Post-marketing analysis of the FDA FAERS database from 2023 to Q1 2025 revealed a persistent signal of hepatotoxicity for etranacogene dezaparvovec: elevated liver enzymes meeting Evans criteria for probable adverse reaction. This means that AAV vector gene therapy for hemophilia B carries a class-wide risk associated with the immune response against the AAV capsid and transduced hepatocytes.
The mechanism is well described in the literature: the AAV capsid is presented on MHC class I of hepatocytes, CD8+ T cells recognize capsid peptides and destroy transduced hepatocytes, leading to transaminase release and loss of factor IX expression. This is exactly what happened to those 6 patients in BENEGENE-2 who returned to prophylaxis: they all received corticosteroids (presumably in response to ALT elevation), but corticosteroids do not always rescue expression.
Here lies the main risk for Pfizer. In BENEGENE-2, patients with antibodies to AAV5 were excluded, but post-marketing data from the competitor show that even seronegative patients may experience delayed loss of response. If Durveqtix exhibits the same problem, Pfizer will have to activate the money-back guarantee — a direct financial obligation that pressures margins.
A second silent issue: the long-term risk of oncogenicity. A 2026 NIH review indicates that integration of the AAV vector into the hepatocyte genome, although considered predominantly episomal, carries a theoretical risk of insertional mutagenesis. No cases of hepatocellular carcinoma have been reported in BENEGENE-2 or HOPE-B, but the 15-year follow-up mandated by regulators has only just begun. Any signal of carcinogenicity would collapse the entire class of AAV therapies.
Forecast: Next 30 and 90 Days
In the next 30 days, the European Commission will issue formal marketing authorization for Durveqtix. Simultaneously, Pfizer will begin negotiations with key European payers — NICE in the UK, IQWiG in Germany, HAS in France. I expect Pfizer to offer a tiered price: €2.8-3.0 million per infusion with a full refund if factor IX falls below 5% within three years. This will force CSL Behring to either lower the price of Hemgenix or strengthen its guarantee program.
Within a 90-day horizon, an event will occur that redefines the dynamics: the first direct public debate between Pfizer and CSL Behring at the ISTH 2026 congress. Both companies will present updated long-term follow-up data. The key question investors will watch: what percentage of patients maintain factor IX levels above 5% at 4-5 years post-infusion? If Pfizer shows data comparable to Hemgenix's mean level of 36%, the market will consider the two drugs interchangeable. If one shows a significant advantage, the other will lose billions of dollars in projected sales.
Hemophilia B is ceasing to be a chronic disease. The war is not between Pfizer and CSL Behring — the war is between the paradigm of "lifetime treatment" and the paradigm of "one shot." And the second option is winning with the same inexorability with which factor IX, produced by the patient's own hepatocytes, displaces weekly infusions. The only open question remains: who will pay for this transition, and how many years will pass before we know whether a single infusion truly means "forever."
— Editorial Team
