08:20 AM EDT, 09/29/2025 (MT Newswires) -- Enanta Pharmaceuticals ( ENTA ) said Monday data from its phase 2 trial of zelicapavir, an oral antiviral treatment for respiratory syncytial virus in high-risk outpatient adults, failed to meet its primary endpoint of effect on the time to resolution of lower respiratory tract disease symptoms in a subset of four symptoms to mild, in the high-risk 3 population.

The high-risk 3 population for the study consisted of elderly patients -- over 75 years old -- with congestive heart failure, chronic obstructive pulmonary disease or asthama. The high-risk 3 population comprised 81% of the efficacy population in the study, the company said.

Despite missing the test's primary endpoint, a 'clinically meaningful' improvement in time to complete resolution of all 13 RSV symptoms was observed for zelicapavir compared with placebo for the high-risk 3 population, and there was a 3-day faster time to complete resolution of lower respiratory tract disease symptoms in the same population.

The company said zelicapavir reduced the time to complete symptom resolution by 2.2 days overall and by 6.7 days in high-risk patients, compared with placebo. The drug met a key secondary endpoint, demonstrating a statistically significant 2-day improvement in the Patient Global Impression of Severity score compared with placebo, the drug developer added.

The study was designed as a proof-of-concept to evaluate symptom-based outcomes and help guide the design of a larger phase 3 trial, the company said.