A Study to Investigate the Safety and Immunogenicity of the Quadrivalent Influenza mRNA Vaccines in Adults Aged 18 Years and Above

Study at a glance

From the registry record, last updated by the sponsor on 4 Aug 2026. Recruitment status is as the sponsor reported it: confirm with the study team.

Official title

A Phase I/II Study to Investigate the Safety and Immunogenicity of Quadrivalent Influenza mRNA Vaccines MRT5421, MRT5424, and MRT5429 in Healthy Participants Aged 18 Years and Above

ClinicalTrials.gov ID

NCT06361875

Acronym / sponsor ID

VAV00045

Conditions

Influenza Immunization, Healthy Volunteers

Phase

Phase 1/2

Study type

Interventional

Recruitment status

Completed

Enrolment

908 participants (actual)

Lead sponsor

Sanofi Pasteur, a Sanofi CompanyIndustry (pharma, biotech, devices)

Study start

1 Apr 2024 (actual)

Primary completion

9 Jun 2025 (actual)

Study completion

9 Jun 2025 (actual)

First posted

12 Apr 2024 (actual)

Results

Posted 4 Aug 2026

Clinical summary

The research question as the sponsor registered it. This describes what the study plans to test, not what it found.

Study design

Primary purpose

Prevention

Allocation

Randomised

Intervention model

Parallel groups

Masking

Triple blind (participant, investigator, outcomes assessor)

Number of arms

10

Model description

Parallel with dose escalation for sentinel cohort

Who may qualify

Ages

18 years and older

Sex

All

Healthy volunteers

Accepted

Age groups

Adult, Older adult

Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.

Interventions

Primary outcome

1. Number of Participants With Immediate Unsolicited Systemic Adverse Events (AEs) After Vaccine Administration

   Time frame: 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.

2. Number of Participants With Solicited Injection Site Reactions After Vaccine Administration

   Time frame: 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.

3. Number of Participants With Solicited Systemic Reactions After Vaccine Administration

   Time frame: 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.

4. Number of Participants With Unsolicited Adverse Events After Vaccine Administration

   Time frame: 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.

5. Number of Participants With Medically Attended Adverse Events (MAAEs)

   Time frame: 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.

6. Number of Participants With Serious Adverse Events (SAEs) and Adverse Event of Special Interest (AESIs)

   Time frame: 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.

7. Number of Participants With Abnormal Biological Test Results

   Time frame: 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.

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

   Time frame: 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.

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

   Time frame: 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.

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

    Time frame: 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.

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

    Time frame: 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.

12. Geometric Mean Ratio of Hemagglutination Inhibition Antibody Titer at Day 29

    Time frame: 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.

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

    Time frame: 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.

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

    Time frame: 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.

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

    Time frame: 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.

Results and safety

Loading the posted results from ClinicalTrials.gov…

Research links

• Official record on ClinicalTrials.govLast updated by the sponsor 4 Aug 2026.
• Posted resultsParticipant flow, baseline, all outcome measures and adverse events.
• VAV00045 Plain Language Results SummaryLink provided by the sponsor.
• Individual participant dataSharing planned: Yes. Qualified researchers may request access to patient level data and related study documents including the clinical study report, study protocol with any amendments, blank case report form, statistical analysis plan, and dataset specifications. Patient level data will be anonymized and study documents will be redacted to protect the privacy of trial participants. Further details on Sanofi's data sharing criteria, eligible studies, and process for requesting access can be found at: https://vivli.org

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Referral and contact

AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.

The record lists no contact. Use the official record to reach the sponsor.

13 sites in 3 countries: see every site and its status.