A Phase 2 Study to Investigate the Efficacy and Safety of Zelicapavir in Participants Aged ≥28 Days to ≤36 Months of Age Infected With Respiratory Syncytial Virus

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.

Study Overview

• Status: Not yet recruiting
• Conditions: Respiratory Syncytial Virus (RSV); RSV Infection; RSV
• Intervention / Treatment: Drug: zelicapavir; Drug: Placebo

• Study Type: Interventional
• Enrollment (Estimated): 150
• Phase: Phase 2

Contacts and Locations

• Study Contact: Name: Enanta Pharmaceuticals, Inc; Phone Number: 617 607-0800; Email: charris@enanta.com

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Participants diagnosed with RSV infection using an approved diagnostic assay, without known and/or documented coinfection with SARS-CoV-2 or influenza
• Participant has signs of RSV infection with onset ≤3 days (72 hours) at the time of randomization
• In the Investigator's opinion, the participant's caregiver understands and is able to comply with protocol requirements, instructions, and restrictions, and the participant is likely to complete the study as planned. The caregiver(s) should be of legal age.

Exclusion Criteria:

• Participant has any condition that in the opinion of the Investigator would interfere with the evaluation of the study drug or participant safety.
• Participant has underlying immune deficiency. Participants with immunoglobulin A deficiency are not excluded.
• Participant has had major surgery within 6 weeks prior to randomization or has major surgery planned during the course of the study.
• Participant is currently taking either chronically or has taken within 7 days prior to randomization, or is anticipated to receive during the course of the study, systemic medications that are known to cause immunosuppression other than corticosteroids for >5 days.
• Participant has received an investigational agent within the last 30 days or 5 half-lives of the investigational agent, whichever is longer.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Triple

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: zelicapavir; zelicapavir, oral suspension, once daily for 7 days	Drug: zelicapavir; Oral suspension
Placebo Comparator: Placebo; Matching placebo, orally, once daily for 7 days	Drug: Placebo; Placebo oral suspension to match zelicapavir

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
Time to complete resolution of clinical signs of RSV as measured by RESOLVE-P	Day 1 through Day 14

Secondary Outcome Measures

Outcome Measure	Time Frame
Time to sustained resolution of clinical signs of RSV as measured by RESOLVE-P	Day 1 through Day 14
Change in severity of clinical signs of RSV from Baseline to D7 as measured by RESOLVE-P	Day 1 through Day 7
Proportion of participants with Lower Respiratory Tract Infection (LRTI)	D1 through D14
Change in severity of RSV from Baseline to D7 and D14	Baseline to D7 and D14
Proportion of outpatient participants who were hospitalized due to RSV or other causes during the study period	Day 1 through Day 35
Change in RSV viral load as measured by RT-qPCR	Baseline to D7
Proportion of participants with viral load Target Not Detected (TND)	Day 4, Day 7 and Day 14
Time to viral load TND	Day 1 through Day 14
Plasma PK Concentrations of zelicapavir	Up to Day 7
Safety as measured by frequency of adverse events (AEs)	Up to Day 35

Collaborators and Investigators

• Sponsor: Enanta Pharmaceuticals, Inc
• Investigators: Study Director: Enanta Pharmaceuticals, Inc, Enanta Pharmaceuticals, Inc

Study record dates

Study Major Dates

• Study Start (Estimated): July 1, 2026
• Primary Completion (Estimated): December 1, 2026
• Study Completion (Estimated): December 1, 2026

Study Registration Dates

• First Submitted: March 16, 2026
• First Submitted That Met QC Criteria: March 16, 2026
• First Posted (Actual): March 19, 2026

Study Record Updates

• Last Update Posted (Actual): March 19, 2026
• Last Update Submitted That Met QC Criteria: March 16, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Keywords: children; RSV; Respiratory Syncytial Virus; Pediatric study
• Additional Relevant MeSH Terms: Infections; RNA Virus Infections; Virus Diseases; Pneumovirus Infections; Paramyxoviridae Infections; Mononegavirales Infections; Respiratory Syncytial Virus Infections
• Other Study ID Numbers: EDP 938-203

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: Yes