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RSVt Vaccine

Phase 1

Respiratory Syncytial Virus Infection | Monoclonal antibody | Infectious Disease |Sanofi|Last Updated: Jan 26, 2026

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Trial Design

RandomizedDouble-BlindPLACEBO_CONTROLLED
Total Trials1
Total Enrollment80

FDA Designations

No designations recorded

Clinical trial landscape

RSVt Vaccine · 1 trial · 1 indication

Phase 1 1
NCT05687279Study on a Live-attenuated Respiratory Syncytial Virus Vaccine for Assessment of Safety, Transmissibility, and Genetic Stability of the Vaccine Virus Among Close Contacts in Infants and Toddlers 6 to < 24 Months of Age in Puerto Rico (USA)Respiratory Syncytial Virus Infection
COMPLETED80 Analytics
PHASE1COMPLETED
Study on a Live-attenuated Respiratory Syncytial Virus Vaccine for Assessment of Safety, Transmissibility, and Genetic Stability of the Vaccine Virus Among Close Contacts in Infants and Toddlers 6 to < 24 Months of Age in Puerto Rico (USA)
Respiratory Syncytial Virus InfectionUnlock trial analytics

Study Endpoints

Primary Endpoints

Percentage of Placebo Receiving Pediatric Participants With Vaccine Virus Detected in Nasal Swabs After the First Vaccination
Pre-vaccination on Day 1 and post-vaccination on Days 4, 8, 11, 15, 18 and 22

Nasal swabs were collected to assess the presence of vaccine virus after first vaccination. Vaccine virus transmission was defined as presence of detected vaccine virus confirmed by RSVt quantitative reverse transcription polymerase chain reaction (qRT-PCR) assay (vaccine virus shedding \>=lower limit of detection \[LOD=2.80 log10 copies/mL\]) in pediatric participants receiving placebo. Percentages are rounded off to the tenth decimal place.

Titer of Vaccine Virus Shedding in All Pediatric Participants Detected in Nasal Swabs
Pre-vaccination on Day 1 and post-vaccination on Days 4, 8, 11, 15, 18, 22, 64 and 71

Nasal swabs were collected to assess the shedding of the attenuated RSV vaccine strain and quantified by RSVt qRT PCR assay. Quantified virus shedding was defined as vaccine virus shedding \>=lower limit of quantification (LLOQ=3.37 log10 copies/mL).

Percentage of Placebo Receiving Pediatric Participants With Detected Shedding Who Showed Any Genetic Sequence Variation After Each Vaccination
Up to 21 days after each vaccination (Day 1 to Day 22 and Day 57 to Day 78)

Nasal swabs were collected to identify the difference in genetic sequence of mutated vaccine virus segments compared to the reference strain vaccine virus isolates in the vaccine virus positive swabs from pediatric participants receiving placebo after each vaccination. Detected virus shedding was defined as vaccine virus shedding \>=LOD (2.80 log10 copies/mL).

Secondary Endpoints

Geometric Mean Titers (GMTs) of RSV A Serum Neutralizing Antibody (nAb) Titers
Pre-vaccination on Day 1 (first vaccination) and Day 57 (second vaccination) and up to 28 days after second vaccination, Day 85
Secondary: Geometric Mean Titers of RSV Serum Anti-F Immunoglobulin G (IgG) Enzyme-linked Immuno-adsorbant Assay (ELISA) Antibody
Pre-vaccination on Day 1 (first vaccination) and Day 57 (second vaccination) and up to 28 days after second vaccination, Day 85
Number of Participants With Immediate Unsolicited Adverse Events (AEs)
Up to 30 minutes after each vaccination (Days 1 and 57)
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Study Design & Arms

AllocationRANDOMIZED
MaskingQUADRUPLE
ModelPARALLEL
PurposePREVENTION

Treatment Arms

ArmTypeDescription
RSVt Vaccine GroupEXPERIMENTAL2 intranasal administrations (56 days apart) of the RSVt vaccine at D01 and D57
Control GroupPLACEBO_COMPARATOR2 intranasal administrations (56 days apart) of the placebo at D01 and D57

Interventions

NameTypeDescription
RSVt VaccineBIOLOGICALPharmaceutical Form: Suspension of virus in a nasal spray Route of Administration: Intranasal
Control GroupOTHERPharmaceutical Form: Suspension of virus in a nasal spray Route of Administration: Intranasal
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Eligibility Criteria

Age Range6 Months to 23 Months
SexALL
Healthy VolunteersYes
Study Sites6

Inclusion Criteria: * Aged 6 months to \< 24 months on the day of inclusion (from the day of the 6 months after birth to the day before the 2nd birthday) * Participants who are healthy as determined by medical evaluation including medical history. * Born at full term of pregnancy (≥ 37 weeks) or bo...

Countries:United StatesPuerto Rico
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Frequently asked questions about RSVt Vaccine

What is RSVt Vaccine used for?

RSVt Vaccine is an investigational live-attenuated vaccine being studied for the prevention of Respiratory Syncytial Virus (RSV) infection in infants and toddlers aged 6 to less than 24 months. It is currently in Phase 1 clinical development and is not yet approved for use.

Who makes RSVt Vaccine?

RSVt Vaccine is being developed by Sanofi, a biopharmaceutical company listed on the stock exchange under the ticker SNY. The vaccine is in Phase 1 clinical development for Respiratory Syncytial Virus infection.

What phase is RSVt Vaccine in?

RSVt Vaccine is in Phase 1 clinical development. It is an investigational vaccine and has not been approved by regulatory authorities. One Phase 1 clinical trial has been completed to assess its safety, transmissibility, and genetic stability.

What clinical trials is RSVt Vaccine in?

RSVt Vaccine has one completed Phase 1 clinical trial, identified as NCT05687279. This study enrolled 80 participants and evaluated the safety, transmissibility, and genetic stability of the vaccine virus among close contacts in infants and toddlers aged 6 to less than 24 months in Puerto Rico, USA.

Is RSVt Vaccine a monoclonal antibody?

No, RSVt Vaccine is a live-attenuated vaccine, not a monoclonal antibody. It is designed to prevent Respiratory Syncytial Virus infection by using a weakened form of the virus to stimulate an immune response. It is currently in Phase 1 clinical development.