ESCMID Global 2026: Zelicapavir Demonstrates Benefits for High-Risk Adults with RSV

Why It Matters

Zelicapavir could become the first oral antiviral for RSV, filling a critical treatment gap and potentially reshaping the RSV therapeutic market.

Key Takeaways

• Phase IIb showed up to 7‑day faster symptom relief in high‑risk adults
• Hospitalisation dropped to 0% versus 5% with placebo
• Severe adverse events were markedly lower in zelicapavir group
• Enanta targets Phase III start Q4 2026, expanding to pediatric trials

Pulse Analysis

Respiratory syncytial virus (RSV) remains a leading cause of serious respiratory illness in older adults and those with chronic conditions, despite recent advances in prophylactic antibodies and vaccines. The lack of approved antivirals forces clinicians to rely on supportive care, creating a sizable unmet need for targeted therapies. An oral agent that can be administered early in the disease course would not only improve patient outcomes but also reduce the burden on hospitals during seasonal spikes.

Enanta's Phase IIb trial of zelicapavir, a novel N‑protein replication inhibitor, offers a glimpse of that potential. Although the study did not meet its primary endpoint, secondary analyses revealed clinically meaningful benefits: high‑risk participants experienced symptom resolution up to a week faster, and the treatment arm saw no RSV‑related hospitalisations compared with a 5% rate in the placebo group. Safety data were reassuring, with serious and grade‑3 adverse events occurring far less frequently among those receiving the drug. These findings suggest that zelicapavir may deliver both efficacy and tolerability advantages that are rare in the antiviral space.

Looking ahead, Enanta’s plan to launch a Phase III trial in late 2026 positions the company to capture a largely untapped market for RSV therapeutics. The parallel pediatric program could broaden the drug’s addressable population, while the company’s pipeline includes an L‑protein inhibitor, EDP‑323, that may synergize with zelicapavir for combination regimens. If Phase III confirms the early signals, Enanta could emerge as a dominant player, offering the first oral RSV treatment and potentially reshaping standard of care for vulnerable patients.