Enanta Pharmaceuticals plans to initiate trials for high-risk adults and pediatric patients in 2026, targeting a population with no current antiviral treatment options.
RT’s Three Key Takeaways:
- Clinical Trial Expansion: Enanta Pharmaceuticals is advancing zelicapavir into late-stage clinical trials for both high-risk adults and pediatric patients, with topline data from both programs expected in 2027.
- High-Risk Patient Focus: The adult registrational study will target individuals with chronic obstructive pulmonary disease, congestive heart failure, or those aged 75 and older who have tested positive for respiratory syncytial virus.
- Hospitalization Reduction: Previous Phase 2 data showed zelicapavir treatment resulted in a 0% hospitalization rate in high-risk adults compared to 5% in the placebo group, according to the company.
Enanta Pharma advanced zelicapavir into a registrational Phase 2b/3 clinical trial for adults at high risk of severe outcomes from respiratory syncytial virus (RSV) following a meeting with the USFDA. The company also plans to initiate a Phase 2b clinical trial of the antiviral in pediatric patients, according to the company.
The Phase 2b/3 trial for adults will evaluate outpatients who test positive for RSV and have had respiratory tract infection symptoms for no more than three days. Eligible patients must have at least one risk factor, including being 75 years of age or older, having chronic obstructive pulmonary disease (COPD), or having congestive heart failure (CHF). Participants will receive an oral dose of 800mg of zelicapavir or a placebo once daily for seven days.
“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,” said Jay R Luly, PhD, president and CEO of Enanta Pharmaceuticals. “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.”
The adult study will include a minimum of 200 patients in the Phase 2b portion to confirm the primary endpoint and treatment effect size, followed by a Phase 3 portion of approximately 660 patients. Participants will be evaluated for 28 days following the treatment period.
In the pediatric population, Enanta plans to initiate a Phase 2b trial in the third quarter of 2026. The study will include approximately 150 participants between 28 days and 36 months of age, including both hospitalized and non-hospitalized children.
“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,” said Scott T Rottinghaus, MD, chief medical officer of Enanta Pharmaceuticals.
Zelicapavir is an oral treatment that inhibits the RSV N-protein, a mechanism that targets viral replication rather than viral entry. According to the news release, the drug has demonstrated a good safety profile and has been well-tolerated in more than 700 subjects to date.
In a previous Phase 2 trial of high-risk adults, zelicapavir treatment resulted in a 6.7-day benefit in symptom resolution for patients with CHF, COPD, or those aged 75 and older. The study also reported an RSV-related hospitalization rate of 0% for patients receiving the drug compared to 5% for those receiving a placebo.
RSV is a leading cause of bronchiolitis and pneumonia in children under one year of age and represents a significant health threat for older adults, according to the CDC. In the US, the virus accounts for approximately 370,000 hospitalizations and 24,000 deaths annually.
