Enanta Pharmaceuticals Announces Advancement of its Zelicapavir Clinical Development Program for the Treatment of Respiratory Syncytial Virus

About this update from Enanta Pharmaceuticals, Inc.

WATERTOWN - Enanta Pharmaceuticals, Inc. (NASDAQ:ENTA), a clinical-stage biotechnology company dedicated to creating small molecule drugs for viral infections and immunological diseases, announced it is advancing zelicapavir into a registrational Phase 2b/3 clinical trial in adults at high risk of severe outcomes from RSV infection after a successful End-of-Phase 2 meeting with the U.S. Food and Drug Administration (FDA). The Phase 2b portion of the trial will confirm the treatment effect with topline data expected in 2027. Enanta also announced plans to initiate a Phase 2b clinical trial of zelicapavir in pediatric patients with RSV, with topline data expected in 2027. 'We are thrilled to move zelicapavir into a single Phase 2b/3 registrational clinical trial in adults with RSV at high risk of progressing to severe disease, following a productive and collaborative End-of-Phase 2 meeting with the FDA. This progress, alongside the planned initiation of our pediatric Phase 2b trial, provides the opportunity for two key Phase 2b datasets next year in two important patient populations and underscores zelicapavir's potential to become the first antiviral therapy for RSV infection,' said Jay R. Luly , Ph.D., President and Chief Executive Officer of Enanta Pharmaceuticals . 'RSV results in a substantial global disease burden, with no available treatment options. We estimate an oral RSV antiviral for children and all high-risk adults represents a global market opportunity of over $2 billion , with a potential total addressable population of greater than 3 million patients in the United States alone. The recent availability of at-home RSV diagnostics is expected to further drive disease awareness and increase earlier diagnosis. As we advance into late-stage development, we are well-positioned to continue our leadership in RSV and remain urgently focused on delivering zelicapavir to patients in need of treatment.' 'We now have a clear and efficient pathway to advance zelicapavir into a registrational program through a single Phase 2b/3 trial. The Phase 2b part is designed to confirm the primary endpoint and treatment effect size in the targeted population and will provide a key dataset to further strengthen the body of evidence supporting the Phase 3 portion of the study. We look forward to beginning the trial in the fourth quarter of 2026, with data from the Phase 2b portion expected in 2027,' said Scott T. Rottinghaus , M.D., Chief Medical Officer of Enanta Pharmaceuticals . 'We are also excited to advance zelicapavir development in children, with a Phase 2b trial to be conducted in collaboration with the Penta Foundation , a leading organization dedicated to pediatric infectious disease research, and the internationally recognized AMS-PHPT Research Unit at Chiang Mai University . This trial will build on the encouraging findings from our first-in-pediatrics study and allow us to assess zelicapavir's treatment effect on symptom resolution using RESOLVE-P, our proprietary tool being developed for use as a registrational endpoint. We plan to initiate this pediatric study in the third quarter of 2026, with topline data expected in 2027.' Adult Registration Study The Phase 2b/3 randomized, double-blind, placebo-controlled, multicenter global trial will evaluate the efficacy and safety of zelicapavir in adult outpatients who test positive for RSV and have had respiratory tract infection symptoms for no more than 3 days. Patients will have at least one of the following risk factors: 75 years of age or older, chronic obstructive pulmonary disease (COPD), or congestive heart failure (CHF). These risk factors are the same as the HR3 population in the Company's previous Phase 2 RSVHR trial where a one-week reduction in time to complete resolution of symptoms and a reduction in hospitalization was observed. Patients will receive an oral dose of 800mg of zelicapavir or placebo once daily for 7 days and be evaluated for 28 days thereafter. The primary endpoint is the time to complete resolution of all 13 RSV symptoms as measured by the RiiQ tool. A key secondary endpoint will evaluate hospitalization rate, with other secondary endpoints of additional clinical efficacy measures, antiviral activity and safety of zelicapavir. The Phase 2b portion of the study will include a minimum of 200 patients and is designed to confirm the primary endpoint and treatment effect size in the targeted population with the optimized dosing duration and will further support the Phase 3 portion of approximately 660 patients. Pediatric Phase 2b Study The Phase 2b, double-blind, placebo-controlled, multicenter trial in pediatric patients is designed to evaluate the efficacy and safety of zelicapavir in hospitalized and non-hospitalized children with up to 72 hours of respiratory tract infection symptoms who test positive for RSV. Approximately 150 participants, 28 days to 36 months of age, will receive 5mg/kg ( (C) 2026 Electronic News Publishing, source ENP Newswire

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