Enanta Pharmaceuticals’ RSV Trial Misses Primary Endpoint but Stock Surges

Enanta Pharmaceuticals reported that its Phase IIb RSVHR trial (NCT05568706) of zelicapavir failed to meet the primary endpoint, showing no significant reduction in time to resolution of the lower respiratory tract disease (LRTD) symptom subset. Patients treated with zelicapavir improved by just 0.5 days versus placebo.

Despite this, the trial demonstrated clinically meaningful benefits in secondary endpoints. Zelicapavir reduced the time to complete resolution of all 13 RSV symptoms by 2.2 days in the overall population and 6.7 days in high-risk patients with CHF, COPD, or age ≥75. Hospitalisation rates decreased, Patient Global Impression of Severity scores improved faster, and virology endpoints confirmed a robust antiviral effect. The therapy was well-tolerated.

Enanta cited these results as supporting Phase III development, with multiple potential registrational endpoints identified. The stock more than doubled, closing at $15.16, up 112% on strong market reaction. Zelicapavir has FDA Fast Track designation, and sales are projected at $209 million by 2030.

30-09-2025