Is RSV a Live Virus?
Yes, Respiratory Syncytial Virus (RSV) is a live virus—specifically, it is a single-stranded RNA virus that actively replicates in human respiratory epithelial cells and causes infection. 1
Viral Characteristics
RSV is classified as an enveloped, negative-sense, single-stranded RNA virus belonging to the Pneumoviridae family. 1, 2 The virus contains 10 genes encoding 11 distinct proteins, including attachment protein (G), fusion protein (F), and various structural and non-structural proteins. 1
- RSV exists in two subtypes (RSV-A and RSV-B) based on variations in the G protein, with alternating patterns of predominance between seasons. 1, 3
- The virus is highly contagious and spreads through droplet transmission, affecting persons of all ages. 4, 5
- RSV is known for its unique ability to induce fusion of respiratory epithelial cells into multinucleated giant cells (syncytia), which is the origin of its name. 1
Clinical Significance of Live Viral Replication
The fact that RSV is a live, replicating virus has important clinical implications:
- Viral shedding typically continues for 1-3 weeks in infants and young children during active infection, requiring isolation precautions throughout hospitalization. 3
- Reinfection is common because the immune response against RSV is short-lived, with protective antibodies and T cells waning within weeks or months, even without antigenic variation. 1, 6
- Natural immunity does not normally follow infection, and reinfection may even occur within a single season. 6
Important Distinction: RSV Vaccines Are NOT Live Virus Vaccines
The currently approved RSV vaccines do NOT contain live virus. 7 This is a critical distinction for clinical practice:
- All three FDA-approved RSV vaccines (Arexvy, Abrysvo, and mResvia) use recombinant protein or mRNA technology, not live attenuated virus. 7, 8
- Arexvy contains recombinant RSV pre-fusion F protein adjuvanted with AS01E. 8
- Abrysvo contains recombinant bivalent RSV-A and RSV-B pre-fusion F protein. 8
- mResvia is an mRNA-based vaccine. 8
This means these vaccines can be safely administered to immunocompromised patients without risk of vaccine-strain viral replication or disease. 8