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RSV vaccine candidate

Phase 2

Respiratory Syncytial Virus Infection | Monoclonal antibody | Infectious Disease |Sanofi|Last Updated: Aug 5, 2026

Success Probability

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Market & Valuation

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Trial Design

RandomizedDouble-BlindPLACEBO_CONTROLLED
Total Trials1
Total Enrollment4,541

FDA Designations

No designations recorded

Clinical trial landscape

RSV vaccine candidate · 2 trials · 3 indications

Phase 2 1Phase 1 1
NCT06251024Study of a Respiratory Syncytial Virus Candidate Formulation in Adults Aged 60 Years and OlderRespiratory Syncytial Virus Infection
COMPLETED4,541 Analytics
PHASE2COMPLETED
Study of a Respiratory Syncytial Virus Candidate Formulation in Adults Aged 60 Years and Older
Respiratory Syncytial Virus InfectionUnlock trial analytics

Study Endpoints

Primary Endpoints

Presence of the first episode of RSV-LRTD (RSV A and/or RSV B) ≥ 14 days after vaccination
≥ 14 days after vaccination

Number of participants experiencing RSV-LRTD (RSV A and/or RSV B) ≥ 14 days after vaccination

Stage 1 (Sentinel and Main Cohort) and Stage 2: Number of Participants With Immediate Unsolicited Systemic Adverse Events (AEs)
Up to 30 minutes post-primary vaccination on Day 1

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. Immediate events were recorded to capture medically relevant unsolicited systemic AEs which occurred within the first 30 minutes after vaccination. 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.

Stage 1 (Sentinel and Main Cohort) and Stage 2: Number of Participants With Solicited Injection Site Reactions and Systemic Reactions
From Day 1 (first dose of primary vaccination) up to Day 8 (7 days post-primary vaccination on Day 1)

An injection site reaction was an adverse reaction (AR) at and around the injection site of the study vaccine. Injection site reactions were commonly inflammatory reactions. Solicited injection site reactions were reactions at and around the injection site of the study vaccine observed and reported under the conditions (nature and onset) pre-listed in the protocol and CRF. Solicited systemic reactions were systemic AEs observed and reported under the conditions (nature and onset) pre-listed in the protocol and CRF. Solicited reactions were considered to be related to the study vaccine administered.

Stage 1 (Sentinel and Main Cohort) and Stage 2: Number of Participants With Unsolicited Adverse Events
From Day 1 (first dose of primary vaccination) up to Day 29 (28 days post-primary vaccination on Day 1)

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 CRF in terms of diagnosis and onset window post-vaccination.

Stage 1 (Sentinel and Main Cohort): Number of Participants With Medically Attended Adverse Events (MAAEs)
From Day 1 (first dose of primary vaccination) up to Day 29 (28 days post-primary vaccination on Day 1)

An MAAE was a new-onset or a worsening of a condition that prompted the participant to seek unplanned medical advice at a physician's office or Emergency Department.

Stage 2: Number of Participants With Medically Attended Adverse Events
From Day 1 (first dose of primary vaccination) to Day 180

An MAAE was a new-onset or a worsening of a condition that prompted the participant to seek unplanned medical advice at a physician's office or Emergency Department.

Stage 1 (Sentinel and Main Cohort) and Stage 2: Number of Participants With Serious Adverse Events (SAEs) and Adverse Events of Special Interest (AESIs)
From Day 1 (first dose of primary vaccination) to Day 365 (Stage 1 Sentinel and Main Cohorts); From Day 1 (first dose of primary vaccination) to Day 180 (Stage 2)

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 SAE was defined as any AE that at any dose resulted in death, was life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, was a congenital anomaly/birth defect, or was an important medical event. An AESI (serious or non-serious) was 1 of scientific and medical concern specific to the Sponsor's study vaccine or program, for which ongoing monitoring and rapid communication by the investigator to the Sponsor was appropriate.

Stage 1 (Sentinel and Main Cohort) and Stage 2: Number of Participants With Shifts From Baseline to Out-of-Range Biological Test Results
From baseline (Day -14 to Day -1) up to Day 8 (7 days post-primary vaccination on Day 1)

Clinical evaluation of laboratory parameters (hematology, clinical chemistry and coagulation parameters) was performed to determine out-of-range values (below or above normal range). Number of participants with a shift from baseline to out-of-range value within 7 days after primary vaccination (Day 8) are reported. Laboratory parameters with a notable shift from baseline included: hematology: hemoglobin, white blood cells (WBC), red blood cells (RBC); clinical chemistry: blood urea nitrogen (BUN), potassium, glucose, C-reactive protein (CRP), direct bilirubin, troponin I; and coagulation parameters: partial thromboplastin time (PTT).

Stage 1 (Sentinel and Main Cohort): Geometric Mean Titers (GMTs) of Neutralizing Antibodies Against Respiratory Syncytial Virus A
Day 1 (pre-primary vaccination) and Day 29 (28 days post-primary vaccination on Day 1)

Neutralizing antibodies activity against RSV A was measured using the RSV plaque reduction neutralization test (PRNT) (micro-PRNT). RSV A serum neutralizing antibodies titers were expressed as 1/dilution.

Stage 2: Geometric Mean Titers of Neutralizing Antibodies Against Respiratory Syncytial Virus A and Respiratory Syncytial Virus B
Day 1 (pre-primary vaccination) and Day 29 (28 days post-primary vaccination on Day 1)

Neutralizing antibodies activity against RSV A and RSV B was measured using the RSV PRNT (micro-PRNT). RSV A and RSV B serum neutralizing antibodies titers were expressed as 1/dilution.

Secondary Endpoints

Presence of the first episode of RSV-ARD (RSV A and/or RSV B) ≥ 14 days after vaccination
≥ 14 days after vaccination
Presence of the first episode of RSV MAARD (RSV A and/or RSV B) ≥ 14 days after vaccination
≥ 14 days after vaccination
Presence of the first episode of RSV LRTD (RSV A) occurring ≥ 14 days after vaccination)
≥ 14 days after vaccination
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Study Design & Arms

AllocationRANDOMIZED
MaskingQUADRUPLE
ModelPARALLEL
PurposePREVENTION

Treatment Arms

ArmTypeDescription
Group 1: RSV vaccine candidateEXPERIMENTALParticipants will be enrolled in a 1:1 ratio to receive a single IM administration of the RSV vaccine candidate.
Group 2: placeboPLACEBO_COMPARATORParticipants will be enrolled in a 1:1 ratio to receive a single IM administration of the placebo.
Stage 1: Sentinel Cohort: RSV Vaccine Dose A1EXPERIMENTALParticipants enrolled in the Sentinel Cohort received 0.5 mL RSV vaccine dose A1 as an IM injection on Day 1 of Stage 1.
Stage 1: Sentinel Cohort: RSV Vaccine Dose A2EXPERIMENTALParticipants enrolled in the Sentinel Cohort received 0.5 mL RSV vaccine dose A2 as an IM injection on Day 1 of Stage 1.
Stage 1: Sentinel Cohort: RSV Vaccine Dose B1EXPERIMENTALParticipants enrolled in the Sentinel Cohort received 0.5 mL RSV vaccine dose B1 as an IM injection on Day 1 of Stage 1.
Stage 1: Sentinel Cohort: RSV Vaccine Dose B2EXPERIMENTALParticipants enrolled in the Sentinel Cohort received 0.5 mL RSV vaccine dose B2 as an IM injection on Day 1 of Stage 1.
Stage 1: Sentinel Cohort: RSV Vaccine Dose C1EXPERIMENTALParticipants enrolled in the Sentinel Cohort received 0.5 mL RSV vaccine dose C1 as an IM injection on Day 1 of Stage 1.
Stage 1: Sentinel Cohort: RSV Vaccine Dose C2EXPERIMENTALParticipants enrolled in the Sentinel Cohort received 0.5 mL RSV vaccine dose C2 as an IM injection on Day 1 of Stage 1.
Stage 1: Sentinel Cohort: PlaceboPLACEBO_COMPARATORParticipants enrolled in the Sentinel Cohort received 0.5 mL placebo matched to RSV vaccine as an IM injection on Day 1 of Stage 1.
Stage 1: Main Cohort: RSV Vaccine Dose A1EXPERIMENTALParticipants enrolled in the Main Cohort received 0.5 mL RSV vaccine dose A1 as an IM injection on Day 1 of Stage 1.
Stage 1: Main Cohort: RSV Vaccine Dose A2EXPERIMENTALParticipants enrolled in the Main Cohort received 0.5 mL RSV vaccine dose A2 as an IM injection on Day 1 of Stage 1.
Stage 1: Main Cohort: RSV Vaccine Dose B1EXPERIMENTALParticipants enrolled in the Main Cohort received 0.5 mL RSV vaccine dose B1 as an IM injection on Day 1 of Stage 1.
Stage 1: Main Cohort: RSV Vaccine Dose B2EXPERIMENTALParticipants enrolled in the Main Cohort received 0.5 mL RSV vaccine dose B2 as an IM injection on Day 1 of Stage 1.
Stage 1: Main Cohort: RSV Vaccine Dose C1EXPERIMENTALParticipants enrolled in the Main Cohort received 0.5 mL RSV vaccine dose C1 as an IM injection on Day 1 of Stage 1.
Stage 1: Main Cohort: RSV Vaccine Dose C2EXPERIMENTALParticipants enrolled in the Main Cohort received 0.5 mL RSV vaccine dose C2 as an IM injection on Day 1 of Stage 1.
Stage 1: Main Cohort: PlaceboPLACEBO_COMPARATORParticipants enrolled in the Main Cohort received 0.5 mL placebo matched to RSV vaccine as an IM injection on Day 1 of Stage 1.
Stage 2: RSV Vaccine Dose C2EXPERIMENTALParticipants received 0.5 mL RSV vaccine dose C2 as an IM injection on Day 1 of Stage 2.
Stage 2: RSV Vaccine Dose DEXPERIMENTALParticipants received 0.5 mL RSV vaccine dose D as an IM injection on Day 1 of Stage 2.
Stage 2: PlaceboPLACEBO_COMPARATORParticipants received 0.5 mL placebo matched to RSV vaccine as an IM injection on Day 1 of Stage 2.

Interventions

NameTypeDescription
RSV vaccine candidateBIOLOGICALPharmaceutical form:Suspension for injection-Route of administration:Intramuscular Injection
PlaceboBIOLOGICALPharmaceutical form:Suspension for injection-Route of administration:Intramuscular Injection
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Eligibility Criteria

Age Range60 Years to N/A
SexALL
Healthy VolunteersYes
Study Sites25

Inclusion Criteria: * Aged 60 years or older on the day of inclusion * A female participant is eligible to participate if she is not pregnant or breastfeeding and: • Is of non-childbearing potential. To be considered of non-childbearing potential, a female must be postmenopausal for at least 1 y...

Countries:AustraliaChileColombiaDominican RepublicHondurasMexicoUnited StatesPuerto Rico
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Frequently asked questions about RSV vaccine candidate

What is the RSV vaccine candidate used for?

The RSV vaccine candidate is being developed for Respiratory Syncytial Virus Infection and Respiratory Syncytial Virus Immunization. It is an investigational monoclonal antibody designed to prevent or treat respiratory syncytial virus, a common respiratory pathogen that can cause serious illness in older adults and other vulnerable populations.

Who makes the RSV vaccine candidate?

Sanofi (ticker: SNY) is developing the RSV vaccine candidate. The company is conducting clinical trials to evaluate the investigational product in adult populations, including studies in the United States, Australia, Puerto Rico, and several Latin American countries.

What phase is the RSV vaccine candidate in?

The RSV vaccine candidate is in Phase 1 clinical development. One Phase 1 trial has been completed, and a Phase 2 trial has also been completed. The drug remains investigational and is not yet approved by regulatory authorities.

What clinical trials is the RSV vaccine candidate in?

The RSV vaccine candidate has been studied in two completed trials. NCT05639894 was a Phase 1 study in adults aged 18 to 50 years and 60 years and older, with 865 participants. NCT06251024 was a Phase 2 study in adults aged 60 years and older, with 4,541 participants.

How does the RSV vaccine candidate work?

The RSV vaccine candidate is a monoclonal antibody, a type of biologic drug that targets respiratory syncytial virus. Monoclonal antibodies are designed to bind to specific viral components to neutralize the virus and help prevent infection. The exact molecular target has not been disclosed.

Is the RSV vaccine candidate the same as other RSV vaccines?

The RSV vaccine candidate is a distinct investigational product developed by Sanofi. It is a monoclonal antibody, which differs from traditional vaccines that stimulate the immune system to produce antibodies. This candidate is being studied specifically for respiratory syncytial virus immunization in adult populations.