Phase 2, Randomized, Double-blind, Placebo-controlled Study to Evaluate the Efficacy and Safety of Zelicapavir in Participants ≥28 Days to ≤36 Months of Age Infected With Respiratory Syncytial Virus

Zelicapavir is a novel, orally administered, nonfusion replication inhibitor of RSV. It is being investigated in this Phase 2 study (EDP 938-203) as a potential treatment for RSV infection in both hospitalized and non-hospitalized children aged ≥28 days to ≤36 months who present with symptomatic RSV infection.

Start Date09 Jul 2026

Sponsor / Collaborator

Enanta Pharmaceuticals, Inc.

[+1]

NCT06601192

/ CompletedPhase 1

Phase 1, Randomized, Double-Blind Four-Period Crossover, Thorough QT/QTc Study to Evaluate the Effects of EDP-938 on Cardiac Repolarization in Healthy Adults

The purpose of the study is to assess the effect of a therapeutic and supratherapeutic dose of zelicapavir on the corrected cardiac QT interval relative to a placebo and positive control in healthy participants.

Start Date15 Jul 2024

Sponsor / Collaborator

Enanta Pharmaceuticals, Inc.

NCT05568706

/ CompletedPhase 2

A Phase 2b, Randomized, Double-Blind, Placebo-Controlled Study to Evaluate the Efficacy and Safety of EDP-938 in Non-hospitalized Adults With Acute Respiratory Syncytial Virus Infection Who Are at High Risk for Complications

This is a Phase 2b, randomized, double-blind, placebo-controlled study of EDP-938 administered orally for the treatment of non-hospitalized adult subjects with confirmed RSV infection who are at high risk for complications after RSV infection.

Start Date29 Nov 2022

Sponsor / Collaborator

Enanta Pharmaceuticals, Inc.

100 Clinical Results associated with Zelicapavir

100 Translational Medicine associated with Zelicapavir

100 Patents (Medical) associated with Zelicapavir

Literatures (Medical) associated with Zelicapavir

01 Feb 2026·RESPIRATORY MEDICINE

Respiratory syncytial virus in high-risk adults: A critical appraisal of therapeutic options and unmet needs

Review

Author: Ranellou, Kyriaki ; Panagiotopoulos, Antonios-Periklis ; Anastassopoulou, Cleo ; Mariolis, Ilias ; Tsakris, Athanasios

Respiratory syncytial virus (RSV) has traditionally been viewed as a causative agent of pediatric illness, yet accumulating evidence shows substantial morbidity and mortality among adults, particularly older individuals, those with cardiopulmonary comorbidities, and the immunocompromised. Although recent vaccine approvals for older adults represent major progress in prevention, effective therapeutic options for established infection remain limited. Herein we provide a critical analysis of existing and emerging antiviral and monoclonal antibody (mAb) therapies for the management of RSV infection in adults, highlighting current options and compounds in clinical development. At present, ribavirin remains the only antiviral recommended for treatment in adults, and no mAb has received regulatory authorization for prophylaxis or therapy in this population. Several development programs for direct-acting antivirals have been discontinued for reasons unrelated to safety or efficacy in adults, contributing to an ongoing treatment gap. Nevertheless, newer drug candidates, including ziresovir, EDP-938, and S-337395, have shown encouraging antiviral activity and acceptable safety in adult studies. By examining both the scientific evidence and the structural factors shaping the current landscape, we emphasize the need for sustained adult-focused clinical development to complement preventive vaccination. Addressing this therapeutic gap will be essential to reduce the burden of RSV disease in high-risk adult populations, particularly as the global population ages.

20 Feb 2025·JOURNAL OF INFECTIOUS DISEASES

EDP-938 Has a High Barrier to Resistance in Healthy Adults Experimentally Infected with Respiratory Syncytial Virus

Article

Author: Levene, Rachel Emily ; DeVincenzo, John ; Or, Yat Sun ; Conery, Annie L ; Ahmad, Alaa ; Rhodin, Michael H J

Abstract:

Background:

EDP-938 is an oral once-daily RSV nucleoprotein (N) inhibitor with potent antiviral activity. In a human RSV challenge trial, EDP-938 significantly reduced viral load and symptom severity. During antiviral development, it is critical to understand the propensity for resistance to develop. In vitro studies of EDP-938 suggest a higher barrier to resistance as compared to RSV fusion inhibitors. We evaluated the development of viral resistance to EDP-938 in a human challenge trial.

Methods:

A subset of the 124 participants with RSV infection were chosen for genetic analysis; 159 nasal wash samples from 48 participants were analyzed using next-generation sequencing of the N gene of RSV. Of the 48 participant sampled, 37 were from EDP-938–treated and 11 were placebo-treated participants, representing 45% and 26% of the participants, respectively. The effects of treatment-emergent mutations on viral load, EDP-938 efficacy, and viral fitness were evaluated.

Results:

Two of the 37 EDP-938–treated participants with samples sequenced had treatment-emergent mutations: N:L139I and N:E112G. From in vitro analysis, N:L139I reduced sensitivity to EDP-938 by approximately 10-fold, while N:E112G had no effect. However, N:L139I was associated with a reduction in viral fitness, suggesting clinical resistance is associated with fitness costs. Neither of these variants were associated with reduced viral clearance.

Conclusions:

In human RSV infections treated with EDP-938, emergence of RSV variants with reduced sensitivity to EDP-938 occurred in only 1 participant and was associated with reduced viral fitness. EDP-938's high barrier to resistance highlights its robust mechanism of action.

Clinical Trials Registration:

NCT03691623.

16 Dec 2024·JOURNAL OF INFECTIOUS DISEASES

Correction to: EDP-938 Has a High Barrier to Resistance in Healthy Adults Experimentally Infected with Respiratory Syncytial Virus

News (Medical) associated with Zelicapavir

18 Jun 2026

·www.biospace.com

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

Registrational Ph2b/3 Trial of Zelicapavir to Initiate in High-Risk Adults with RSV in 4Q 2026, with Topline Phase 2b Data Expected in 2027 Phase 2b Trial of Zelicapavir to Initiate in Pediatric Patients with RSV in 3Q 2026, with Topline Data Expected in 2027 WATERTOWN, Mass.--(BUSINESS WIRE)-- Enanta Pharmaceuticals, Inc. (NASDAQ:ENTA), a clinical-stage biotechnology company dedicated to creating small molecule drugs for viral infections and immunological diseases, today 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 (<12 months old) or 7.5 mg/kg (≥12 months old) 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 clinical signs of RSV as measured by the RESOLVE-P clinical scoring scale. Secondary endpoints will evaluate additional clinical efficacy measures, antiviral activity, and safety of zelicapavir. The trial is being conducted in Thailand in collaboration with the Penta Foundation, and the AMS-PHPT Research Unit at Chiang Mai University, which has deep expertise and decades of experience in conducting infectious disease trials. In addition, its network is comprised of clinical trial sites in geographies where the RSV season begins in the summer, making them an ideal partner to execute a timely start for this trial. Enanta plans to initiate this Phase 2b study in the third quarter of 2026 with topline data expected in 2027. About Zelicapavir Zelicapavir is being developed for the treatment of RSV infection and has been granted Fast Track designation by the U.S. Food and Drug Administration. Zelicapavir inhibits the RSV N-protein with nanomolar activity against both RSV-A and RSV-B. This mechanism is differentiated from RSV fusion inhibitors as targeting the N-protein inhibits viral replication versus viral entry and has a high barrier to resistance in vitro . In a Phase 2 trial of hospitalized and non-hospitalized pediatric RSV patients aged 28 days to 3 years old, zelicapavir demonstrated an antiviral effect and shortened time to complete resolution of RSV symptoms. In a Phase 2 trial of high-risk adults, a clinically meaningful improvement in time to complete resolution of all 13 RSV symptoms was observed for zelicapavir compared to placebo, with a benefit of 6.7 days for patients with congestive heart failure, chronic obstructive pulmonary disease, or age 75 years or older, termed the HR3 population. Importantly, zelicapavir treatment resulted in a lower hospitalization rate, with an RSV-related hospitalization rate of 5% in placebo, compared to 0% in patients who received zelicapavir. Throughout its clinical development program, zelicapavir has demonstrated a good safety pro has been well-tolerated in more than 700 subjects to date. About RSV RSV is the most common cause of bronchiolitis (inflammation of the small airways in the lung) and pneumonia in children under one year of age in the United States and a significant cause of respiratory illness in older adults and immunocompromised individuals. 1,2 According to the Centers for Disease Control and Prevention, virtually all children in the United States get an RSV infection by the time they are two years old. 3 RSV represents a significant health threat for adults older than 50 years of age, with up to 180,000 hospitalizations associated with RSV infections annually in the United States. 2 Overall, in the United States, RSV accounts for up to 6.8 million outpatient visits and approximately 370,000 hospitalizations, with 24,000 deaths. 4 About Enanta Pharmaceuticals, Inc. Enanta is using its robust, chemistry-driven approach and drug discovery capabilities to become a leader in the discovery and development of small molecule drugs for viral infections and immunological diseases. In virology, Enanta’s clinical programs are focused on the development of first-in-disease and best-in-disease treatments for RSV. The Company’s immunology pipeline aims to develop treatments for inflammatory diseases by targeting key drivers of the type 2 immune response, with KIT, STAT6 and MRGPRX2 inhibition. Glecaprevir, a protease inhibitor discovered by Enanta, is part of one of the leading treatment regimens for curing hepatitis C virus (HCV) infection and is sold by AbbVie in numerous countries under the tradenames MAVYRET ® (U.S.) and MAVIRET ® (ex-U.S.) (glecaprevir/pibrentasvir). A portion of Enanta’s royalties from HCV products developed under its collaboration with AbbVie contribute ongoing funding to Enanta’s operations. Please visit for more information. Forward Looking Statements This press release contains forward-looking statements, including statements with respect to the timeline and prospects for advancement of zelicapavir for the treatment of RSV. Statements that are not historical facts are based on management’s current expectations, estimates, forecasts and projections about Enanta’s business and the industry in which it operates and management’s beliefs and assumptions. The statements contained in this release are not guarantees of future performance and involve certain risks, uncertainties and assumptions, which are difficult to predict. Therefore, actual outcomes and results may differ materially from what is expressed in such forward-looking statements. Important factors and risks that may affect actual results include: clinical drug development involves a lengthy and expensive process with uncertain timelines and uncertain outcomes, Enanta’s clinical trials, including its Phase 2b/3 trial, may fail to demonstrate sufficient safety and efficacy and, if that occurs, it may be unable to commercialize our product candidates on a timely basis or ever, the impact of development, regulatory and marketing efforts of others with respect to vaccines and competitive treatments for RSV; the discovery and development risks of Enanta’s programs in virology and immunology; Enanta’s limited clinical development experience; Enanta’s ability to partner its RSV or other programs; Enanta’s need to attract and retain senior management and key research and development personnel; Enanta’s need to obtain and maintain patent protection for its product candidates and avoid potential infringement of the intellectual property rights of others; and other risk factors described or referred to in “Risk Factors” in Enanta’s Form 10-K for the fiscal year-ended September 30, 2025, and any other periodic reports filed more recently with the Securities and Exchange Commission. Enanta cautions investors not to place undue reliance on the forward-looking statements contained in this release. These statements speak only as of the date of this release, and Enanta undertakes no obligation to update or revise these statements, except as may be required by law. References 1. Centers for Disease Control & Prevention – About RSV . Last accessed: June 2026. 2. Centers for Disease Control & Prevention – RSV In Adults . Last accessed: June 2026. 3. Centers for Disease Control & Prevention – RSV in Infants and Young Children . Last accessed: June 2026. 4. CDC Preliminary Estimates of RSV Burden for 2024-2025 ; for period: 9/29/24-9/27/25. Last accessed June 2026. Contacts Media and Investor Contact Jennifer Viera 617-744-3848 jviera@enanta.com

Phase 2Fast TrackClinical Result

11 May 2026

·ir.enanta.com

Enanta Pharmaceuticals Reports Financial Results for its Fiscal Second Quarter Ended March 31, 2026

Dosing Initiated in a Phase 1 Trial of EDP-978, an Oral, Once-Daily KIT Inhibitor in Development for the Treatment of Chronic Urticaria; On Track to Report Topline Data in 4Q 2026 Conducting Enabling Activities for a Pivotal Study of Zelicapavir in High-Risk Adults with Respiratory Syncytial Virus (RSV) On Track to File an IND for EPS-3903, an Oral, Once-Daily STAT6 Inhibitor Development Candidate and to Select an MRGPRX2 Development Candidate, in 2H 2026 Cash and Marketable Securities Totaling $227 Million at March 31, 2026 , as well as Continuing Retained Royalties, with Cash Runway Expected to Fund Operations into Fiscal 2029 WATERTOWN, Mass. --(BUSINESS WIRE)--May 11, 2026-- Enanta Pharmaceuticals, Inc. (NASDAQ:ENTA), a clinical-stage biotechnology company dedicated to creating small molecule drugs for viral infections and immunological diseases, today reported financial results for its fiscal second quarter ended March 31, 2026 . “Since the inception of our immunology portfolio targeting type 2 diseases, our team has worked diligently to advance highly selective inhibitors of KIT, STAT6 and MRGPRX2 designed to enable convenient oral dosing and best-in-class profiles,” said Jay Luly , Ph.D., President and Chief Executive Officer of Enanta. “This quarter, we achieved a key milestone with dosing initiation in our Phase 1 trial of EDP-978, an oral KIT inhibitor in development for chronic urticaria. Along with advancing EDP-978 into the clinic, we remain on track to file an IND for EPS-3903, our oral STAT6 inhibitor, and to nominate an MRGPRX2 development candidate, in the second half of 2026. In parallel, we are continuing to conduct enabling activities for a pivotal study of zelicapavir in adults at high risk of serious complications from RSV infection and look forward to providing an update on the development path later this quarter. With a strong balance sheet and ongoing royalty revenues, we are well-positioned to execute on our strategy and to deliver multiple value-driving milestones over the coming year.” Fiscal Second Quarter Ended March 31, 2026 Financial Results Total revenue for the three months ended March 31, 2026 was $17.2 million and consisted of royalty revenue from worldwide net sales of MAVYRET®/MAVIRET® (glecaprevir/pibrentasvir), AbbVie’s treatment for hepatitis C virus, compared to $14.9 million for the three months ended March 31, 2025 . The increase in revenue is due to an increase in AbbVie’s product sales quarter over quarter. A portion (54.5%) of Enanta’s ongoing royalty revenue from AbbVie’s net sales of MAVYRET®/MAVIRET® is paid to OMERS, one of Canada’s largest defined benefit pension plans, pursuant to a royalty sale transaction affecting royalties earned after June 2023 . For financial reporting purposes, the transaction was treated as debt, with the upfront purchase payment of $200.0 million recorded as a liability. Each quarter, Enanta records 100% of the royalty earned as revenue and then amortizes the debt liability proportionally as 54.5% of the cash royalty payments are paid to OMERS through June 30, 2032 , subject to a cap of 1.42 times the purchase payment, after which point 100% of the cash royalty payments will be retained by Enanta. Interest expense was $3.3 million for the three months ended March 31, 2026 , as compared to $1.7 million for the three months ended March 31, 2025 . The increase was due to the increase in royalty revenue from AbbVie’s net sales of MAVYRET®/MAVIRET®. Research and development expenses totaled $19.4 million for the three months ended March 31, 2026 , compared to $28.1 million for the three months ended March 31, 2025 . The decrease was due to a decrease in clinical trial expenses for Enanta’s RSV programs, partially offset by increased costs associated with the Company’s immunology programs. General and administrative expenses totaled $9.6 million for the three months ended March 31, 2026 , compared to $11.4 million for the three months ended March 31, 2025 . The decrease was primarily due to a decrease in stock-based compensation expenses. Interest and investment income, net, totaled $2.1 million for the three months ended March 31, 2026 , compared to $2.3 million for the three months ended March 31, 2025 . The decrease in interest and investment income was due to lower interest rates year over year. Enanta recorded an income tax expense of less than $0.1 million for the three months ended March 31, 2026 compared to an income tax benefit of $1.3 million for the three months ended March 31, 2025 . Enanta recorded an additional federal income tax refund of $0.9 million during the three months ended March 31, 2025 . The federal income tax refund of $33.8 million , including interest, was received in April 2025 . Net loss for the three months ended March 31, 2026 was $13.1 million , or a loss of $0.45 per diluted common share, compared to a net loss of $22.6 million , or a loss of $1.06 per diluted common share, for the corresponding period in 2025. Enanta’s cash, cash equivalents and short-term and long-term marketable securities totaled $227.0 million at March 31, 2026 . Enanta expects that its current cash, cash equivalents and marketable securities, as well as its retained portion of future royalty revenue will be sufficient to meet the anticipated cash requirements of its existing business and development programs into fiscal 2029. Virology Enanta’s virology pipeline includes the leading portfolio of RSV treatments in clinical development, consisting of zelicapavir, a once-daily N-protein inhibitor, and EDP-323, a once-daily L-protein inhibitor, both of which received Fast Track designation from the U.S. Food and Drug Administration (FDA). Zelicapavir was most recently evaluated in a high-risk adult outpatient population, including the elderly and those with asthma, chronic obstructive pulmonary disease, or congestive heart failure. In RSVHR, a Phase 2b study, zelicapavir demonstrated a clinically meaningful improvement in time to complete resolution of all 13 RSV symptoms compared to placebo, with an improvement of 6.7 days for patients with congestive heart failure, chronic obstructive pulmonary disease or age 75 or older, termed the HR3 population. Zelicapavir also showed an improvement in time to complete resolution on the 29-parameter total RiiQ™ symptom scale of 7.2 days for the HR3 population compared to placebo. The study met key secondary endpoints, including a reduction in hospitalization and antiviral effects. Previously, the Company reported positive data from a Phase 2 study in pediatric patients which demonstrated that treatment with zelicapavir was associated with shortened time to complete resolution of RSV symptoms. Overall, zelicapavir has been dosed in more than 700 people to date and continues to be well-tolerated with a favorable safety profile. Enanta presented data on zelicapavir at the European Society of Clinical Microbiology & Infectious Diseases (ESCMID) Global 2026 which was held April 17-21, 2026 , in Munich, Germany . The poster and presentation are available on the Company’s website here. Enanta will present an oral presentation highlighting zelicapavir at the American Thoracic Society (ATS) International Conference 2026, being held May 15-20, 2026 , in Orlando, Florida . Enanta continues to conduct enabling activities for a pivotal study of zelicapavir in high-risk patients with RSV, including engaging with the FDA on the registrational development path. The Company plans to provide an update on the study design and development path in the second quarter of 2026. In parallel, Enanta is exploring potential business development opportunities related to its RSV program. Enanta’s second RSV candidate, EDP-323, can be used alone or in combination with other agents, such as zelicapavir, to potentially broaden the treatment window or addressable patient populations. Previously, the Company reported positive results from a Phase 2a challenge study of healthy adults infected with RSV, in which treatment with EDP-323 achieved highly statistically significant reductions in both viral load and clinical symptoms compared to placebo. Enanta presented data on zelicapavir at the European Society of Clinical Microbiology & Infectious Diseases (ESCMID) Global 2026 which was held April 17-21, 2026 , in Munich, Germany . The poster and presentation are available on the Company’s website here. Enanta will present an oral presentation highlighting zelicapavir at the American Thoracic Society (ATS) International Conference 2026, being held May 15-20, 2026 , in Orlando, Florida . Enanta continues to conduct enabling activities for a pivotal study of zelicapavir in high-risk patients with RSV, including engaging with the FDA on the registrational development path. The Company plans to provide an update on the study design and development path in the second quarter of 2026. In parallel, Enanta is exploring potential business development opportunities related to its RSV program. Immunology Enanta’s immunology pipeline is focused on designing and developing highly potent and selective oral inhibitors for the treatment of inflammatory diseases, by targeting key drivers of the type 2 immune response. Enanta’s lead immunology program, EDP-978, is a potent and selective once-daily oral KIT inhibitor in development for the treatment of chronic urticaria and potentially other mast cell-mediated diseases. In April, the Company announced the first participant was dosed in a randomized, double-blind, placebo-controlled, first-in-human Phase 1 clinical trial. The trial is expected to enroll approximately 98 healthy adult volunteers ranging in age from 18 to 65 years old to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics, including serum tryptase, of EDP-978. The trial includes a single ascending dose phase, with a two-part food-effect cohort, and a multiple ascending dose phase with a 14-day treatment period. The Company expects to report topline data from the trial in the fourth quarter of 2026. Enanta presented two posters featuring pre-clinical data related to EDP-978 at the American Academy of Allergy , Asthma & Immunology (AAAAI) 2026 Annual Meeting which was held February 27-March 2, 2026 . The posters are available on the Company’s website here. Enanta’s second immunology program EPS-3903, is a novel, potent, and selective oral STAT6 inhibitor, in development for the treatment of atopic dermatitis and other diseases currently treated by dupilumab. The Company is currently performing scale-up and IND enabling activities and is targeting an IND filing in the second half of 2026. Enanta presented four posters highlighting pre-clinical data related to EPS-3903 at IMMUNOLOGY2026TM, hosted by the American Association of Immunologists (AAI), held April 15-19, 2026 . The posters are available on the Company’s website here. Enanta will present two posters highlighting data on EPS-3903 at the ATS International Conference 2026, being held May 15-20, 2026 , in Orlando, Florida . Enanta’s third immunology program targets MRGPRX2, a non-canonical G-Protein-Coupled-Receptor (GPCR) expressed predominantly on mast cells, as well as peripheral neurons. Inhibiting MRGPRX2 may have potential to address multiple chronic inflammatory diseases including urticaria, asthma, prurigo nodularis and others, as well as migraine. Currently, the Company is evaluating multiple compounds in pre-clinical studies and expects to select a development candidate in the second half of 2026. Enanta presented two posters featuring pre-clinical data related to EDP-978 at the American Academy of Allergy , Asthma & Immunology (AAAAI) 2026 Annual Meeting which was held February 27-March 2, 2026 . The posters are available on the Company’s website here. Enanta presented four posters highlighting pre-clinical data related to EPS-3903 at IMMUNOLOGY2026TM, hosted by the American Association of Immunologists (AAI), held April 15-19, 2026 . The posters are available on the Company’s website here. Enanta will present two posters highlighting data on EPS-3903 at the ATS International Conference 2026, being held May 15-20, 2026 , in Orlando, Florida . Corporate Today, the United States Court of Appeals for the Federal Circuit held oral arguments in Enanta’s lawsuit against Pfizer Inc., seeking damages for infringement of U.S. Patent No. 11,358,953 in the manufacture, use and sale of Pfizer’s COVID-19 antiviral, PAXLOVID® (nirmatrelvir tablets; ritonavir tablets). Based on the current schedule, Enanta anticipates a decision on the appeal from the Federal Circuit by the end of September 2026 . A hearing for the patent infringement action against Pfizer Inc. and certain of its subsidiaries in the Unified Patent Court (UPC) of the European Union , and Pfizer’s counterclaim for revocation, has been scheduled for September 29, 2026 . Enanta expects a decision from the UPC within weeks after the hearing. Enanta plans to issue its fiscal third quarter financial results press release on August 10, 2026 . About Enanta Pharmaceuticals, Inc. Enanta is using its robust, chemistry-driven approach and drug discovery capabilities to become a leader in the discovery and development of small molecule drugs for viral infections and immunological diseases. In virology, Enanta’s clinical programs are focused on the development of first-in-disease and best-in-disease treatments for respiratory syncytial virus (RSV). The Company’s immunology pipeline aims to develop treatments for inflammatory diseases by targeting key drivers of the type 2 immune response, with KIT, STAT6 and MRGPRX2 inhibition. Glecaprevir, a protease inhibitor discovered by Enanta, is part of one of the leading treatment regimens for curing hepatitis C virus (HCV) infection and is sold by AbbVie in numerous countries under the tradenames MAVYRET® ( U.S. ) and MAVIRET® (ex- U.S. ) (glecaprevir/pibrentasvir). A portion of Enanta’s royalties from HCV products developed under its collaboration with AbbVie contribute ongoing funding to Enanta’s operations. Please visit www.enanta.com for more information. Forward Looking Statements This press release contains forward-looking statements, including statements with respect to the timeline and prospects for advancement of Enanta’s clinical programs in RSV and KIT inhibition and its pre-clinical immunology programs, including its programs targeting STAT6 and MRGPRX2 inhibition, as well as statements regarding Enanta’s ongoing litigation matters. Statements that are not historical facts are based on management’s current expectations, estimates, forecasts and projections about Enanta’s business and the industry in which it operates and management’s beliefs and assumptions. The statements contained in this release are not guarantees of future performance and involve certain risks, uncertainties and assumptions, which are difficult to predict. Therefore, actual outcomes and results may differ materially from what is expressed in such forward-looking statements. Important factors and risks that may affect actual results include: the impact of development, regulatory and marketing efforts of others with respect to vaccines and competitive treatments for RSV; the discovery and development risks of Enanta’s programs in virology and immunology; Enanta’s limited clinical development experience; Enanta’s ability to partner its RSV or other programs; Enanta’s need to attract and retain senior management and key research and development personnel; Enanta’s need to obtain and maintain patent protection for its product candidates and avoid potential infringement of the intellectual property rights of others; the timing and outcome of Enanta’s ongoing litigation matters; and other risk factors described or referred to in “Risk Factors” in Enanta’s Form 10-K for the fiscal year-ended September 30, 2025 , and any other periodic reports filed more recently with the Securities and Exchange Commission. Enanta cautions investors not to place undue reliance on the forward-looking statements contained in this release. These statements speak only as of the date of this release, and Enanta undertakes no obligation to update or revise these statements, except as may be required by law. Tables to Follow ENANTA PHARMACEUTICALS, INC. Three Months Ended Six Months Ended March 31 , March 31 , 2026 2025 2026 2025 $ 17,159 $ 14,926 $ 35,774 $ 31,885 19,443 28,065 40,302 55,721 9,568 11,388 18,577 24,234 29,011 39,453 58,879 79,955 (11,852 ) (24,527 ) (23,105 ) (48,070 ) (3,316 ) (1,714 ) (6,399 ) (3,676 ) 2,084 2,292 4,506 5,091 (13,084 ) (23,949 ) (24,998 ) (46,655 ) (7 ) 1,305 (31 ) 1,721 $ (13,091 ) $ (22,644 ) $ (25,029 ) $ (44,934 ) $ (0.45 ) $ (1.06 ) $ (0.87 ) $ (2.11 ) $ (0.45 ) $ (1.06 ) $ (0.87 ) $ (2.11 ) 29,040 21,355 28,892 21,295 29,040 21,355 28,892 21,295 UNAUDITED (in thousands) March 31 , September 30 , 2026 2025 $ 34,928 $ 32,298 128,846 156,566 7,809 6,882 6,810 8,590 19 — 178,412 204,336 63,238 — 33,114 35,395 36,436 37,549 3,360 3,360 144 92 $ 314,704 $ 280,732 $ 4,363 $ 1,948 6,859 12,751 31,461 30,710 3,759 3,146 46,442 48,555 97,309 111,132 52,777 54,757 1,311 1,311 278 260 198,117 216,015 116,587 64,717 $ 314,704 $ 280,732 View source version on businesswire.com: https://www.businesswire.com/news/home/20260511989798/en/ Media and Investors Contact: Jennifer Viera jviera@enanta.com Source: Enanta Pharmaceuticals, Inc.

04 May 2026

·www.biospace.com

Enanta Pharmaceuticals to Present Data for its Respiratory Syncytial Virus and STAT6 Inhibitor Programs at the American Thoracic Society International Conference 2026

WATERTOWN, Mass.--(BUSINESS WIRE)-- Enanta Pharmaceuticals, Inc. (NASDAQ:ENTA), a clinical-stage biotechnology company dedicated to creating small molecule drugs for viral infections and immunological diseases today announced that the Company will have an oral presentation highlighting zelicapavir and two posters with data on EPS-3903, a novel, potent and selective oral STAT6 inhibitor, at the American Thoracic Society (ATS) International Conference 2026 being held May 15-20, 2026 in Orlando, Florida. Details of the presentations are as follows: Title: Zelicapavir Reduces Symptom Duration and Hospitalization in a Randomized, Double-Blind, Placebo-Controlled, International, Phase 2 Trial Abstract Number: 12336 Session C96: Lung-Specific Immunity in Viral Infection: From Real-Time Host Responses to Novel Antiviral Strategies Session Type: Mini Symposium Date and Time: Tuesday, May 19, 2026, from 2:15 PM – 2:27 PM EDT Presenter: Christopher Harris, M.D. Title: EPS-3903 is a Potent and Selective Oral STAT6 Inhibitor That Blocks Th2 Inflammation in a House Dust Mite-Induced Asthma Mouse Model Poster Number: P72 Session C34: Asthma Unveiled: A Thematic Journey from Omics to Precise Characterization of Phenotype and Therapies Session Type: Thematic Poster Session Date and Time: Tuesday, May 19, 2026, from 11:30 AM – 1:15 PM EDT Presenter: Yaohui Nie, Ph.D. Title: EPS-3903, a Potent, Oral STAT6 Inhibitor, Exhibits Preferential Lung and Alveolar Macrophage Distribution with Low Drug–Drug Interaction Potential for the Treatment of Asthma Poster Number: P75 Session Type: Thematic Poster Session Session C34: Asthma Unveiled: A Thematic Journey from Omics to Precise Characterization of Phenotype and Therapies Date and Time: Tuesday, May 19, 2026, from 11:30 AM – 1:15 PM EDT Presenter: Lisha Xu and Yang Li, Ph.D. Further information about ATS 2026 can be found here . Presentations will be available on the Company’s website here following each presentation. About Enanta Pharmaceuticals, Inc. Enanta is using its robust, chemistry-driven approach and drug discovery capabilities to become a leader in the discovery and development of small molecule drugs for viral infections and immunological diseases. In virology, Enanta’s clinical programs are focused on the development of first-in-disease and best-in-disease treatments for respiratory syncytial virus (RSV). The Company’s immunology pipeline aims to develop treatments for inflammatory diseases by targeting key drivers of the type 2 immune response, with KIT, STAT6 and MRGPRX2 inhibition. Glecaprevir, a protease inhibitor discovered by Enanta, is part of one of the leading treatment regimens for curing hepatitis C virus (HCV) infection and is sold by AbbVie in numerous countries under the tradenames MAVYRET® (U.S.) and MAVIRET® (ex-U.S.) (glecaprevir/pibrentasvir). A portion of Enanta’s royalties from HCV products developed under its collaboration with AbbVie contribute ongoing funding to Enanta’s operations. Please visit for more information. Contacts Media and Investors: Jennifer Viera 617-744-3848 jviera@enanta.com

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Indication	Highest Phase	Country/Location	Organization	Date
Respiratory Syncytial Virus Infections	Phase 2	United Kingdom	Enanta Pharmaceuticals, Inc.	15 Oct 2018

Clinical Result

Indication

Phase

Evaluation

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Study	Phase	Population	Analyzed Enrollment	Group	Results	Evaluation	Publication Date


NCT05568706 (RSVHR, Company_Website) Manual	Phase 2	Respiratory Syncytial Virus Infections	186	Zelicapavir	pqrcdodblz(qzfdtpduve) = No effect was observed on the time to resolution of symptoms (defined as mild), including the primary endpoint of time to resolution of the LRTD subset of four symptoms in the efficacy population. oezuuxygol (xidhsgbnxv ) Not Met View more	Positive	29 Sep 2025
				Placebo
NCT04816721 (Company_Website) Manual	Phase 2	Respiratory Syncytial Virus Infections	96	zelicapavir	cjoceozuif(iudsyzfppp) = qodvopqrks qauaktyxsg (gdceppepxz ) View more	Positive	09 Dec 2024
				placebo	cjoceozuif(iudsyzfppp) = jnurcvlatg qauaktyxsg (gdceppepxz ) View more
NCT04633187 (RSVTx, CTgov)	Phase 2	Respiratory Syncytial Virus Infections	9	EDP-938 (EDP-938)	ooodkysdai = tahcbszrtn bqiesfiigw (gxynvvbizr, neamqnnfuc - ubnvzqawaq) View more	-	22 Aug 2024
				Placebo (Placebo)	ooodkysdai = ezrhgikggk bqiesfiigw (gxynvvbizr, rqyvhtmpns - gwuznlujoj) View more
NCT04196101 (RSVP, CTgov)	Phase 2	Respiratory Syncytial Virus Infections	82	EDP-938 (EDP-938)	kqjozkigpn(aydepqdqky) = vcbddtcmgn segvprcnrj (cvwtpdnsge, 97.180) View more	-	30 Oct 2023
				Placebo (Placebo)	kqjozkigpn(aydepqdqky) = fpgtmmfkhr segvprcnrj (cvwtpdnsge, 40.310) View more
NCT04196101 (RSVP, Biospace) Manual	Phase 2	Respiratory Syncytial Virus Infections	81	EDP-938	rohujplnkr(uomnwegxgm) = The AUC for the mean total symptom score (days x score) was not statistically different between the two groups jjmmzhdwuw (izarneknsa ) View more	Negative	18 May 2022
				Placebo
NCT03691623 (CTgov)	Phase 2	Respiratory Syncytial Virus Infections	179	EDP-938 (Part 1: EDP-938 600 mg)	wmmhixgkoi(ffrrszsuda) = lgexugcuka adtecyhleb (bgwsjlmasw, 85.1) View more	-	03 May 2022
				EDP-938 (Part 1: EDP-938 500 mg Then 300 mg)	wmmhixgkoi(ffrrszsuda) = krjqmqphzy adtecyhleb (bgwsjlmasw, 99.9) View more
NCT03691623 (Pubmed \| N Engl J Med)	Phase 2	Respiratory Syncytial Virus Infections	-	EDP-938	ywheiyelvx(vtyrqcslfe) = ysdddcqped kbwyvmbqwr (okjbxbnhto ) View more	Positive	17 Feb 2022
				Placebo	ywheiyelvx(vtyrqcslfe) = pwngxebuwj kbwyvmbqwr (okjbxbnhto ) View more

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