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NCT05687279

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)

Completed Phase 1, PHASE2 Results posted Last updated 26 January 2026
What this trial tests

Phase 1, PHASE2 trial testing RSVt Vaccine in Respiratory Syncytial Virus Infection in 80 participants. Completed in 27 December 2024.

Timeline
6 February 2023
Primary endpoint
27 December 2024
27 December 2024

Quick facts

Lead sponsorSanofi Pasteur, a Sanofi Company
PhasePhase 1, PHASE2
StatusCompleted
Study typeINTERVENTIONAL
Allocationrandomized
Designparallel
Maskingquadruple
Primary purposeprevention
Enrollment80
Start date6 February 2023
Primary completion27 December 2024
Estimated completion27 December 2024
Sites6 locations across Puerto Rico, United States

Drugs / interventions tested

Conditions studied

Sponsor

Sanofi Pasteur, a Sanofi Company — full company profile →

Who can join

Adults 6 Months to 23 Months, any sex, with Respiratory Syncytial Virus Infection. Patients with the condition only — healthy volunteers not accepted.

Results — posted to ClinicalTrials.gov

Per-arm endpoint measurements with 95% confidence intervals where reported. Source: trial results section.

Percentage of Placebo Receiving Pediatric Participants With Vaccine Virus Detected in Nasal Swabs After the First Vaccination Primary · 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.

Day 1
GroupValue95% CI
Placebo00 – 10.9
Day 4
GroupValue95% CI
Placebo00 – 9.7
Day 8
GroupValue95% CI
Placebo00 – 9.7
Day 11
GroupValue95% CI
Placebo00 – 9.7
Day 15
GroupValue95% CI
Placebo00 – 10.0
Day 18
GroupValue95% CI
Placebo00 – 9.7
Day 22
GroupValue95% CI
Placebo00 – 10.3
Titer of Vaccine Virus Shedding in All Pediatric Participants Detected in Nasal Swabs Primary · 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).

Day 8
GroupValue95% CI
RSVt4.33± 0.649
Day 11
GroupValue95% CI
RSVt4.33± 0.617
Day 22
GroupValue95% CI
RSVt4.72
Day 64
GroupValue95% CI
RSVt3.55± 0.014
Geometric Mean Titers (GMTs) of RSV A Serum Neutralizing Antibody (nAb) Titers Secondary · Pre-vaccination on Day 1 (first vaccination) and Day 57 (second vaccination) and up to 28 days after second vaccination, Day 85

Serum samples were collected at specified timepoints for immunogenicity assessments. RSV A serum neutralizing antibody titers were evaluated by microneutralization (MN) assay.

Day 1
GroupValue95% CI
RSVt53.429.7 – 95.9
Placebo47.925.2 – 90.8
Day 57
GroupValue95% CI
RSVt16795.5 – 294
Placebo65.330.8 – 138
Day 85
GroupValue95% CI
RSVt219126 – 382
Placebo60.026.6 – 135
Secondary: Geometric Mean Titers of RSV Serum Anti-F Immunoglobulin G (IgG) Enzyme-linked Immuno-adsorbant Assay (ELISA) Antibody Secondary · Pre-vaccination on Day 1 (first vaccination) and Day 57 (second vaccination) and up to 28 days after second vaccination, Day 85

Serum samples were collected at specified timepoints for immunogenicity assessments. Antibodies to RSV F antigen were measured using the anti RSV F IgG ELISA method.

Day 1
GroupValue95% CI
RSVt92.245.5 – 187
Placebo85.639.3 – 186
Day 57
GroupValue95% CI
RSVt249130 – 475
Placebo11549.7 – 265
Day 85
GroupValue95% CI
RSVt383205 – 714
Placebo12952.6 – 317
Number of Participants With Immediate Unsolicited Adverse Events (AEs) Secondary · Up to 30 minutes after each vaccination (Days 1 and 57)

An AE was any untoward medical occurrence in a clinical study participant temporally associated with the use of study vaccine, whether or not considered related to the study vaccine. An unsolicited AE was an observed AE that did not fulfill the conditions of solicited reactions, i.e., pre-listed in the case report form (CRF) in terms of diagnosis and onset window post-vaccination. All participants were observed for 30 minutes after each vaccination and any unsolicited AEs that occurred during that time were recorded as immediate unsolicited AEs.

GroupValue95% CI
RSVt0
Placebo0
Number of Participants With Solicited Administration Site Reactions and Systemic Reactions Secondary · Up to 21 days after each vaccination (Day 1 to Day 22 and Day 57 to Day 78)

A solicited reaction was an expected adverse reaction (AR) (sign or symptom) observed and reported under the conditions (nature and onset) pre-listed in the protocol and CRF and considered as related to the study vaccine administered. An administration site reaction was an AR at and around the administration/injection site and were commonly inflammatory reactions. Solicited systemic reactions were systemic AEs and those occurring during the specified collection period were always considered related to the vaccine even if there was evidence of alternative etiology.

Solicited administration site reaction
GroupValue95% CI
RSVt30
Placebo32
Solicited systemic reaction
GroupValue95% CI
RSVt26
Placebo25
Number of Participants With Unsolicited Adverse Events Secondary · Up to 28 days after each vaccination (Day 1 to Day 29 and Day 57 to Day 85)

An AE was any untoward medical occurrence in a clinical study participant temporally associated with the use of study vaccine, whether or not considered related to the study vaccine. An unsolicited AE was an observed AE that did not fulfill the conditions of solicited reactions, that is, pre-listed in the CRF in terms of diagnosis and onset window post-vaccination.

GroupValue95% CI
RSVt8
Placebo12

Adverse events — posted to ClinicalTrials.gov

Time frame: From date of first vaccination (Day 1) up to 6 months after the last study vaccination, approximately 237 days. Reporting threshold: 5%. Adverse-event reports describe events observed during the trial — not all are caused by the drug.

RSVt
Serious: 2/39 (5%)
Deaths: 0/39
Placebo
Serious: 4/39 (10%)
Deaths: 0/39

Serious adverse events (4 terms)

ReactionSystemRSVtPlacebo
BronchiolitisInfections and infestations——
GastroenteritisInfections and infestations——
InfluenzaInfections and infestations——
Oral HerpesInfections and infestations——
Other adverse events (1 terms — click to expand)

ReactionSystemRSVtPlacebo
Decreased AppetiteMetabolism and nutrition disorders——

Most-reported serious reactions: Bronchiolitis, Gastroenteritis, Influenza, Oral Herpes.

Data from ClinicalTrials.gov NCT05687279 adverse events section.

Sponsor's own description

The primary purpose of the study is to assess the shedding, transmission, and genetic stability of the live-attenuated RSVt vaccine after each intranasal vaccination (56 days apart) in infants and toddlers 6 to \< 24 months of age.

Publications & conference data

6 peer-reviewed publications reference this trial (live from Europe PMC):

  1. Clinical research on RSV prevention in children and pregnant women: progress and perspectives.
    Gong X, Luo E, Fan L, Zhang W, et al · · 2023 · cited 9× · PMID 38327765 · DOI 10.3389/fimmu.2023.1329426
  2. Global progress in clinical research on human respiratory syncytial virus vaccines.
    Peng R, Chen C, Chen Q, Zhang Y, et al · · 2024 · cited 8× · PMID 39286350 · DOI 10.3389/fmicb.2024.1457703
  3. Recent advances in the prevention of respiratory syncytial virus in pediatrics.
    Lipp MA, Empey KM. · · 2024 · cited 7× · PMID 38299987 · DOI 10.1097/mop.0000000000001336
  4. Nanotechnology-driven advances in intranasal vaccine delivery systems against infectious diseases.
    Zhang Z, Yang Y, Huang L, Yuan L, et al · · 2025 · cited 4× · PMID 40416956 · DOI 10.3389/fimmu.2025.1573037
  5. Combating respiratory diseases with mucosal vaccines.
    Tang PCH, Ling Z, Lee M, King NJC, et al · · 2026 · PMID 41983630 · DOI 10.1128/jvi.00146-26
  6. Respiratory Syncytial Virus (RSV): A Comprehensive Overview From Basic Biology to Clinical Prevention and Control.
    Shi J, Huang X, Ye C, Lu Y, et al · · 2026 · PMID 41261734 · DOI 10.1002/med.70025

Verify or expand the search:

Other trials of RSVt Vaccine

Trials testing the same drug.

Other recruiting trials for Respiratory Syncytial Virus Infection

Currently open trials in the same condition.

Other Sanofi Pasteur, a Sanofi Company trials

Trials by the same sponsor.

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Primary sources · FDA · ClinicalTrials.gov · EMA · SEC EDGAR · ChEMBL · Wikidata · full sourcing