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Quadrivalent Influenza mRNA Vaccine MRT5421

Phase 1

Influenza Immunization | Monoclonal antibody | Infectious Disease |Sanofi|Last Updated: Aug 4, 2026

Success Probability

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Trial Design

RandomizedDouble-BlindACTIVE_CONTROLLED
Total Trials1
Total Enrollment908

FDA Designations

No designations recorded

Clinical trial landscape

Quadrivalent Influenza mRNA Vaccine MRT5421 · 1 trial · 2 indications

Phase 1 1
NCT06361875A Study to Investigate the Safety and Immunogenicity of the Quadrivalent Influenza mRNA Vaccines in Adults Aged 18 Years and AboveInfluenza Immunization
COMPLETED908 Analytics
PHASE1COMPLETED
A Study to Investigate the Safety and Immunogenicity of the Quadrivalent Influenza mRNA Vaccines in Adults Aged 18 Years and Above
Influenza ImmunizationUnlock trial analytics

Study Endpoints

Primary Endpoints

Number of Participants With Immediate Unsolicited Systemic Adverse Events (AEs) After Vaccine Administration
Within 30 minutes after vaccine administration on Day 1

An AE is 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 is an observed AE that does not fulfill the conditions of solicited reactions, that is, pre-listed in the case report form in terms of diagnosis and onset window post-vaccination. Systemic AEs are all AEs that were not injection or administration site reactions. Immediate events are recorded to capture medically relevant unsolicited systemic AEs which occur within the first 30 minutes after vaccination.

Number of Participants With Solicited Injection Site Reactions After Vaccine Administration
Within 7 days after vaccine administration on Day 1

An adverse reaction (AR) is any noxious and unintended response to a study vaccine related to any dose. Solicited injection site reactions are reactions at and around the injection site of the vaccine observed and reported under the conditions (nature and onset) pre-listed in the protocol and case report form.

Number of Participants With Solicited Systemic Reactions After Vaccine Administration
Within 7 days after vaccine administration on Day 1

An AR is any noxious and unintended response to a study vaccine related to any dose. Solicited systemic reactions are systemic AEs observed and reported under the conditions (nature and onset) pre-listed in the protocol and case report form.

Number of Participants With Unsolicited Adverse Events After Vaccine Administration
Within 28 days after vaccine administration on Day 1

An AE is 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 is an observed AE that does not fulfill the conditions of solicited reactions, that is, pre-listed in the case report form in terms of diagnosis and onset window post-vaccination.

Number of Participants With Medically Attended Adverse Events (MAAEs)
Within 180 days after vaccine administration on Day 1

An MAAE is a new onset or a worsening of a condition that prompts the participant or participant's parent/legally acceptable representative to seek unplanned medical advice at a physician's office or emergency department.

Number of Participants With Serious Adverse Events (SAEs) and Adverse Event of Special Interest (AESIs)
From the vaccine administration (Day 1) until 12 months after vaccine administration, approximately 366 days

An SAE is any untoward medical occurrence that at any dose results in death or is life-threatening or requires inpatient hospitalization or prolongation of existing hospitalization or results in persistent or significant disability/incapacity or is a congenital anomaly/birth defect or is an important medical event. An AESI (serious or non-serious) is 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 can be appropriate. The AESIs was defined as anaphylactic reactions (including bronchospasms, and laryngeal spasms), Guillain-Barré syndrome, neuritis (including Bell's palsy), myocarditis, pericarditis, myopericarditis and vasculitis.

Number of Participants With Abnormal Biological Test Results
Within 8 days after vaccine administration on Day 1

Blood samples were collected for the assessment of abnormal hematology and clinical chemistry parameters. Only participants with outside the normal range hematology and clinical chemistry parameters are reported.

Geometric Mean of Hemagglutination Inhibition (HAI) Antibody (Ab) Titer at Day 1
Day 1

The HAI Ab was measured by hemagglutinin inhibition using quality control sera (sheep, ferret and/or human sera) measurement method. The 95% confidence interval (CI) was based on the Clopper-Pearson method.

Geometric Mean of Hemagglutination Inhibition Antibody Titer at Day 29
Day 29

The HAI Ab was measured by hemagglutinin inhibition using quality control sera (sheep, ferret and/or human sera) measurement method. The 95% CI was based on the Clopper-Pearson method.

Percentage of Participants With Detectable Hemagglutination Inhibition Antibody Titer >=1:10 at Day 1
Day 1

The HAI Ab was measured by hemagglutinin inhibition using quality control sera (sheep, ferret and/or human sera) measurement method. The 95% CI for the single percentage was based on the Clopper-Pearson method. The percentages are rounded off to the tenth decimal place.

Percentage of Participants With Detectable Hemagglutination Inhibition Antibody Titer >=1:10 at Day 29
Day 29

The HAI Ab was measured by hemagglutinin inhibition using quality control sera (sheep, ferret and/or human sera) measurement method. The 95% CI for the single percentage was based on the Clopper-Pearson method. The percentages are rounded off to the tenth decimal place.

Geometric Mean Ratio of Hemagglutination Inhibition Antibody Titer at Day 29
Days 1 and 29

The HAI Ab was measured by hemagglutinin inhibition using quality control sera (sheep, ferret and/or human sera) measurement method. The geometric mean ratio of antibody titer at post-vaccination over pre-vaccination is reported. The 95% CI was based on the Clopper-Pearson method.

Percentage of Participants With Seroconversion of Hemagglutination Inhibition Antibody Titer at Day 29
Day 29

The seroconversion was defined as titer \<10 on Day 1 and post-injection titer \>=40 on Day 29; or defined as titer \>=10 on Day 1 and a \>=4-fold increase in titer on Day 29. The 95% CI for the single percentage was based on the Clopper-Pearson method. The percentages are rounded off to the tenth decimal place.

Percentage of Participants With Hemagglutination Inhibition Antibody Titer >=1:40 at Day 29
Day 29

The HAI Ab was measured by hemagglutinin inhibition using quality control sera (sheep, ferret and/or human sera) measurement method. The 95% CI for the single percentage was based on the Clopper-Pearson method. The percentages are rounded off to the tenth decimal place.

Percentage of Participants With >=2 and >=4 Fold Increase in Hemagglutination Inhibition Antibody Titer at Day 29
Days 1 and 29

The HAI Ab was measured by hemagglutinin inhibition using quality control sera (sheep, ferret and/or human sera) measurement method. The 95% CI for the single percentage was based on the Clopper-Pearson method. The percentages are rounded off to the tenth decimal place.

Secondary Endpoints

Geometric Mean of Neutralization Test (NT) Antibody Titer at Days 1 and 29
Days 1 and 29
Geometric Mean Ratio of Neutralization Test Antibody Titer at Day 29
Days 1 and 29
Percentage of Participants With >=2 and >=4 Fold Increase in Neutralization Test Antibody Titer at Day 29
Days 1 and 29
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Study Design & Arms

AllocationRANDOMIZED
MaskingTRIPLE
ModelPARALLEL
PurposePREVENTION

Treatment Arms

ArmTypeDescription
Quadrivalent Influenza mRNA Vaccine MRT5421 Dose 1EXPERIMENTALparticipants received a single dose of QIV mRNA vaccine MRT5421
Quadrivalent Influenza mRNA Vaccine MRT5429 Dose 1EXPERIMENTALparticipants received a single dose of QIV mRNA vaccine MRT5429
Quadrivalent Influenza mRNA Vaccine MRT5429 Dose 2EXPERIMENTALparticipants received a single dose of QIV mRNA vaccine MRT5429
Quadrivalent Influenza mRNA Vaccine MRT5429 Dose 3EXPERIMENTALparticipants received a single dose of QIV mRNA vaccine MRT5429
Quadrivalent Influenza mRNA Vaccine MRT5429 Dose 4EXPERIMENTALparticipants received a single dose of QIV mRNA vaccine MRT5429
Quadrivalent Influenza mRNA Vaccine MRT5424 Dose 1EXPERIMENTALparticipants received a single dose of QIV mRNA vaccine MRT5424
Quadrivalent Influenza mRNA Vaccine MRT5424 Dose 2EXPERIMENTALparticipants received a single dose of QIV mRNA vaccine MRT5424
Quadrivalent Influenza SD VaccineACTIVE_COMPARATORparticipants received a single dose of QIV-SD vaccine
Quadrivalent Influenza HD VaccineACTIVE_COMPARATORparticipants received a single dose of QIV -HD vaccine (for adults ≥ 65 years of age only)
Quadrivalent Influenza RIV4 VaccineACTIVE_COMPARATORparticipants received a single dose of RIV4 vaccine

Interventions

NameTypeDescription
Quadrivalent Influenza mRNA Vaccine MRT5421BIOLOGICALPharmaceutical form:solution in a vial-Route of administration:Intramuscular injection
Quadrivalent Influenza mRNA Vaccine MRT5424BIOLOGICALPharmaceutical form:solution in a vial-Route of administration:Intramuscular injection
Quadrivalent Influenza mRNA Vaccine MRT5429BIOLOGICALPharmaceutical form:solution in a vial-Route of administration:Intramuscular Injection
Quadrivalent Influenza Standard Dose VaccineBIOLOGICALPharmaceutical form: suspension for injection in prefilled syringe -Route of administration:Intramuscular injection
Quadrivalent Influenza High-Dose VaccineBIOLOGICALPharmaceutical form:suspension for injection in pre filled syringe -Route of administration:Intramuscular injection
Quadrivalent Recombinant Influenza VaccineBIOLOGICALPharmaceutical form:suspension for injection in pre filled syringe-Route of administration:Intramuscular injection
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Eligibility Criteria

Age Range18 Years to N/A
SexALL
Healthy VolunteersYes
Study Sites13

Inclusion Criteria: * Aged from 18 years on the day of inclusion or aged from 21 years on the days of inclusion, depending on the countries. * A female participant was eligible to participate if she was not pregnant or breastfeeding and one of the following conditions applied: * Was of non-child...

Countries:United StatesHondurasPuerto Rico
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Recent Changes (Last 90 Days)

MEDIUMSep 4, 2026NCT06361875TRIAL_REMOVED: changed

Frequently asked questions about Quadrivalent Influenza mRNA Vaccine MRT5421

What is Quadrivalent Influenza mRNA Vaccine MRT5421 used for?

Quadrivalent Influenza mRNA Vaccine MRT5421 is an investigational vaccine being developed for influenza immunization in adults aged 18 years and above. It is designed to provide protection against influenza, though it is still in clinical development and not yet approved for public use.

Who is developing Quadrivalent Influenza mRNA Vaccine MRT5421?

Quadrivalent Influenza mRNA Vaccine MRT5421 is being developed by Sanofi, a global biopharmaceutical company listed on the stock exchange under the ticker SNY. The vaccine is currently in Phase 1 clinical development for influenza immunization.

What phase is Quadrivalent Influenza mRNA Vaccine MRT5421 in?

Quadrivalent Influenza mRNA Vaccine MRT5421 is in Phase 1 clinical development. It is an investigational vaccine, meaning it has not been approved by regulatory authorities and is still undergoing clinical trials to evaluate its safety and immunogenicity.

What clinical trials is Quadrivalent Influenza mRNA Vaccine MRT5421 in?

Quadrivalent Influenza mRNA Vaccine MRT5421 has one completed Phase 1 clinical trial, identified as NCT06361875. This study investigated the safety and immunogenicity of the vaccine in adults aged 18 years and above, enrolling 908 participants across the United States, Honduras, and Puerto Rico.

Is Quadrivalent Influenza mRNA Vaccine MRT5421 the same as MRT5421?

Yes, Quadrivalent Influenza mRNA Vaccine MRT5421 is also known as MRT5421. The vaccine is being developed by Sanofi for influenza immunization and is currently in Phase 1 clinical trials.