Enanta Pharmaceuticals (ENTA) investor relations material

Study design and patient population

• Phase 2b, randomized, double-blind, placebo-controlled study evaluated zelicapavir in 186 high-risk, non-hospitalized adults with acute RSV infection, focusing on those with CHF, COPD, asthma, or age ≥65/75.

• Enrollment prioritized the highest-risk group (HR3: CHF, COPD, or age ≥75), comprising 80–81% of the efficacy population.

• Patients were randomized within 72 hours of symptom onset to receive zelicapavir or placebo for five days, with follow-up through day 28–33.

• Baseline characteristics and demographics were well balanced between groups, with most enrolled within 48 hours of symptom onset.

• Most patients had not received RSV vaccination; mean baseline symptom scores and viral loads were similar across groups.

Efficacy and clinical outcomes

• Zelicapavir significantly reduced the duration of all RSV symptoms, with up to 6.7 days improvement in HR3 and 2.2 days overall; 35% improvement in HR3 population.

• Statistically significant two-day faster time to symptom resolution by PGI-S in both overall and HR3 populations.

• No effect on primary endpoint (time to mild LRTD symptoms) in the overall efficacy population.

• Hospitalization rates were lower with zelicapavir (1.7% vs. 5% for placebo), with no RSV-attributed hospitalizations in the zelicapavir group.

• No deaths occurred in the zelicapavir group, and no patients required ICU admission or mechanical ventilation.

Virology results

• Zelicapavir showed a robust antiviral effect, with a 0.6–0.7 log drop in viral load and a faster median time to undetectable viral load (four to five days faster than placebo).

• A higher proportion of patients had undetectable viral load at end of treatment: 23.5% vs 10.0% (p = 0.0198) in the efficacy population.