Enanta’s Antiviral Drug, Zelicapavir, Shows Positive Results in Pediatric RSV Phase 2 Study

Enanta Pharmaceuticals, Inc., a biotech company focused on developing minor molecule treatments for virology and immunology. The firm has announced encouraging topline results from its Phase 2 trial of zelicapavir in young children with respiratory syncytial virus (RSV). The study involved hospitalised and non-hospitalized patients aged 28 days to 36 months.

Scott T. Rottinghaus, M.D., Chief Medical Officer of Enanta Pharmaceuticals, said in a statement, “We are excited to share these positive results from our first-in-pediatric Phase 2 study of zelicapavir, which we believe confirm a strong profile for our lead RSV antiviral and strengthen Enanta’s position as a leader in developing treatments for RSV. Zelicapavir demonstrated an antiviral effect on both primary and secondary virology endpoints. Furthermore, patients who joined the study within 3 days of symptom onset showed a robust 1.2 log reduction in viral load on Day 5. 

He further added, “These data provide us with continued confidence in Zelicapavir and valuable insights to inform the design of a potential registration-enabling trial. There is a substantial need for safe and effective oral treatments for RSV, and we believe that these important antiviral data, along with the favorable safety profile observed in this young, vulnerable population support further clinical evaluation of zelicapavir.”

Results showed significant antiviral effects across primary and secondary virology endpoints in the combined efficacy group. In Part 2 of the trial, which focused on virology outcomes, zelicapavir reduced viral load by 1.4 logs at Day 5 compared to placebo. Additionally, a subgroup of patients treated within three days of symptom onset experienced a 1.2 log viral load reduction by Day 5, highlighting the treatment's rapid and strong antiviral impact.

“In my practice, I see many children requiring hospitalization for severe RSV infection during the RSV season. The impact of RSV is felt not only by patients and caregivers, but also broadly by public health. I believe that a safe and effective antiviral therapeutic is critical in addressing this significant and unmet need. These results support further evaluation of zelicapavir and suggest the potential for zelicapavir to improve patient outcomes. I’m excited to see this compound move forward, to possibly deliver the first safe and effective antiviral to treat children with RSV infection,” said Jaime Deville, MD, FAAP, a Principal Investigator in the Phase 2 pediatric clinical trial of zelicapavir and Professor of Clinical Infectious Diseases in the Department of Pediatrics at the David Geffen School of Medicine, University of California, Los Angeles and UCLA Mattel Children’s Hospital. 

The study found that zelicapavir was well-tolerated, with a favourable safety profile in this pediatric population. As a novel N-protein inhibitor, zelicapavir is designed for once-daily oral use to treat RSV. The drug has received Fast Track designation from the FDA, emphasising its potential to address an unmet medical need.