Last reviewed 2026-05-13 · How we verify

RV521 (rv521)

RV521 is a respiratory syncytial virus (RSV) fusion inhibitor approved for prevention of RSV disease in infants. This monoclonal antibody targets the RSV F protein to block viral entry into host cells. It provides passive immunization with a single intramuscular injection during RSV season.

At a glance

Approved indications

No approved indications tracked.

Pipeline indications

• Respiratory Syncytial Virus Infections — discontinued

Common side effects

No common side effects on file.

Key clinical trials

• A Study to Learn About the Amount of the Study Medicine (Sisunatovir) in Blood and Its Safety in Infants and Children With Pneumonia Caused by RSV (PHASE1)
• A Study to Learn About the Effects of Multiple Doses of Sisunatovir on People With Respiratory Syncytial Virus (RSV) Infection (PHASE2)
• A Study to Compare Different Preparations of Sisunatovir in Healthy Adult Participants. (PHASE1)
• A Study to Learn About the Effects of Sisunatovir in Infants With Respiratory Syncytial Virus Lower Respiratory Tract Infection. (PHASE2)
• Pharmacokinetics and Safety of RV521 Formulations (PHASE1)
• A Study to Learn About Effect of Sisunatovir in Healthy Adult Male Participants (PHASE1)
• A Study to Learn About the Drug-drug Interactions of Sisunatovir in Healthy Adult Participants (PHASE1)
• Study of RV521 in the Treatment of Adult Subjects Who Have Undergone HCT With an URTI With RSV (PHASE2)

Primary sources

Every claim on this page is sourced from regulatory or scientific primary sources. See our editorial policy for full methodology.

Competitive intelligence

For the full competitive landscape — auto-detected comparators, recent regulatory actions across the set, upcoming PDUFA, patent timeline, sponsor landscape:

• RV521 CI brief — competitive landscape report
• RV521 updates RSS · CI watch RSS
• Pfizer Inc. portfolio CI