Influenza, HumanPhase 2NCT05501561

Safety and Immunogenicity of Different Formulations of an MF59-Adjuvanted Influenza Vaccine in Older Adults ≥50 Years of Age

A Phase 2 study testing Experimental: IIV-A Investigational IIV-A administered as a single dose intramuscularly on Day 1, Experimental: aIIV-B Investigational aIIV-B administered as a single dose intramuscularly on Day 1 and Experimental: aIIV-C Investigational aIIV-C administered as a single dose intramuscularly on Day 1 in people with Influenza, Human, run by Seqirus at 47 sites in United States.

Completed

Finished. The study has ended and is not enrolling. Results may be posted on the official record.

Official record

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Trial summary

Who is it for?: Ages 50 years and olderHealthy volunteers can take part
Conditions the study is for: Influenza, Human
What is being tested?: Experimental: IIV-A Investigational IIV-A administered as a single dose intramuscularly on Day 1, Experimental: aIIV-B Investigational aIIV-B administered as a single dose intramuscularly on Day 1 and Experimental: aIIV-C Investigational aIIV-C administered as a single dose intramuscularly on Day 1
Type of treatment: Vaccines, Injection or infusion
Could I receive a placebo?: No, everyone receives an active treatment
How many people: 1,056 participants
Where: 47 sitesUnited States
Study dates: 25 Aug 2022to 31 Mar 2023
Phase: Phase 2
Are there results?: Yes, posted in the registrySummary in the doctors' view

Key requirements

Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.

Ages 50 years and older
All sexes
Healthy volunteers accepted
Adult, Older adult

Who may be able to join

In order to participate in this study, all subjects must meet ALL of the inclusion criteria described.
Individuals ≥50 years of age on the day of informed consent.
Individuals who have voluntarily given written consent after the nature of the study has been explained according to local regulatory requirements, prior to study entry.
Individuals who can comply with study procedures including follow-up .
Males, females of non-childbearing potential or females of childbearing potential who are using an effective birth control method, at least 30 days prior to informed consent, which they intend to use for at least 2 months after the study vaccination.
-

Who cannot join

In order to participate in this study, all subjects must not meet ANY of the exclusion criteria described below:
Females of childbearing potential who are pregnant, lactating, or who have not adhered to a specified set of contraceptive methods from at least 30 days prior to informed consent and who do not plan to do so for at least 2 months after the study vaccination.
Progressive, unstable or uncontrolled clinical conditions.
Hypersensitivity, including allergy, to any component of vaccines whose use is foreseen in this study.
History of any medical condition considered an adverse event of special interest (AESI).
Known history of Guillain-Barré syndrome or another demyelinating disease such as encephalomyelitis and transverse myelitis.

Show all 20Show fewer

Clinical conditions representing a contraindication to intramuscular administration of vaccines or blood draw.
Abnormal function of the immune system resulting from:
Clinical conditions.
Systemic administration of corticosteroids (PO/IV/IM) at a dose of ≥20 mg/day of prednisone or equivalent for more than 14 consecutive days within 90 days prior to informed consent5.
Administration of antineoplastic and immunomodulating agents or radiotherapy within 90 days prior to informed consent.
Receipt of immunoglobulins or any blood products within 180 days prior to informed consent.
Receipt of an investigational or non-registered medicinal product within 30 days prior to informed consent.
Receipt of any COVID-19 vaccine within 14 days (non-replicating vaccines) or 28 days (replicating vaccines) prior to informed consent or plan to receive any COVID-19 vaccine within 7 days from study vaccination
Individuals who received any other vaccines within 14 days (for inactivated vaccines) or 28 days (for live vaccines) prior to informed consent or who are planning to receive any vaccine within 28 days from the study vaccines.
Study personnel or immediate family or household member of study personnel.
Receipt of any influenza vaccine within 6 months prior to informed consent, or plan to receive an influenza vaccine during the study period.
Acute (severe) febrile illness,
Any other clinical condition that, in the opinion of the investigator, might interfere with the results of the study or pose additional risk to the subject due to participation in the study.
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Trial locations and contacts

47 sites in 1 country.

City, postcode or hospital

47 sites in 1 country

United States47 sites

Meridian Clinical Research
Baton Rouge, Louisiana, 70808
Meridian Clinical Research
Bellevue, Nebraska, 68005
MedPharmics LLC
Biloxi, Mississippi, 39531
Meridian Clinical Research (Binghamton, NY)
Binghamton, New York, 13901
CVS pharmacy - Charlottesville
Charlottesville, Virginia, 22902
Meridian Clinical Research, LLC
Cincinnati, Ohio, 45219
Meridian Clinical Research, LLC
Cincinnati, Ohio, 45246
Innovative Research of West Florida, Inc.
Clearwater, Florida, 33756
The Lynn Institute of The Rockies
Colorado Springs, Colorado, 80920
Aventiv Research, Inc. Columbus
Columbus, Ohio, 43213
Meridian Clinical Research - Dakota Dunes
Dakota Dunes, South Dakota, 57049
Velocity Clinical Research - New Smyrna Beach
Edgewater, Florida, 32132
AMR El Dorado
El Dorado, Kansas, 67042
Meridian Clinical Research, LLC
Endwell, New York, 13760
Velocity Clinical Research, Gaffney
Gaffney, South Carolina, 29340
Meridian Clinical Research
Grand Island, Nebraska, 68803
Velocity Clinical Research - Greenville
Greenville, South Carolina, 29615
Healthcare Research Network
Hazelwood, Missouri, 63042
CenExel RCA
Hollywood, Florida, 33024
Marvel Clinical Research
Huntington Beach, California, 92647
Health Awareness INC
Jupiter, Florida, 33458
The Center for Pharmaceutical Research
Kansas City, Missouri, 64114
AMR Coastal Clinical Research
Knoxville, Tennessee, 37920
Alliance for Multispecialty Research, LLC, Las Vegas
Las Vegas, Nevada, 89119
AMR Lexington
Lexington, Kentucky, 40509
Meridian Clinical Research, LLC
Lincoln, Nebraska, 68510
Velocity Clinical Research - Medford
Medford, Oregon, 97504
Medpharmics, LLC
Metairie, Louisiana, 70006
Global Health Research Center
Miami Lakes, Florida, 33016
Clinical Research Consulting, LLC
Milford, Connecticut, 06460
Lynn Health Science Institute
Oklahoma City, Oklahoma, 73112
M3 Wake Research, Inc.
Raleigh, North Carolina, 27612
CVS pharmacy - Reston
Reston, Virginia, 20190
CVS pharmacy - Richmond
Richmond, Virginia, 23235
Rockville Internal Medicine Group
Rockville, Maryland, 20854
JBR Clinical Research
Salt Lake City, Utah, 84107
California Research Center
San Diego, California, 92123
Platinum Research Network, LLC
Savannah, Georgia, 31405
Meridian Clinical Research - Savannah
Savannah, Georgia, 31406
Velocity Clinical Research, Spartanburg
Spartanburg, South Carolina, 29303
Sundance Clinical Research, LLC
St Louis, Missouri, 63141
Precision Clinical Research
Sunrise, Florida, 33351
Velocity Clinical Research - Syracuse
Syracuse, New York, 13057
Global Health Research Center
Tampa, Florida, 33615
AMR Tempe
Tempe, Arizona, 85281
DM Clinical Research
Tomball, Texas, 77375
Velocity Clinical Research - West Jordan
West Jordan, Utah, 84088

Other trials in United States

About this study

Official title: A Phase 2b, Randomized, Observer-Blind, Antigen and Adjuvant Dose-Confirmation Clinical Study to Evaluate Safety and Immunogenicity of Different Formulations of MF59-Adjuvanted Quadrivalent Subunit Inactivated Cell-derived Influenza Vaccine (aQIVc) in Older Adults ≥50 Years of Age

This Phase 2, randomized, observer-blind, dose-confirmation clinical study evaluated different formulations of MF59-Adjuvanted Quadrivalent Subunit Inactivated Influenza Vaccine. Approximately 1000 subjects were randomized into 1 of 4 possible treatment groups with approximately 250 participants per group. Every participant received an influenza vaccine injection on Day 1 and were to be followed up for approximately 6 months following injection. The primary immunogenicity analysis is based on Day 29 serology data.

Conditions: Influenza, Human
Being tested: Experimental: IIV-A Investigational IIV-A administered as a single dose intramuscularly on Day 1, Experimental: aIIV-B Investigational aIIV-B administered as a single dose intramuscularly on Day 1, Experimental: aIIV-C Investigational aIIV-C administered as a single dose intramuscularly on Day 1, Active Comparator: Licensed IIV IIV administered as a single dose intramuscularly on Day 1
Keywords: influenza, vaccine, MF59, adjuvant
Medical subject headings: Influenza, Human

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

Experimental: IIV-A Investigational IIV-A administered as a single dose intramuscularly on Day 1Biological
Biological/Vaccine: Investigational IIV-A Investigational Quadrivalent Influenza vaccine (higher hemagglutinin [HA] dose), containing four influenza virus strains (A/H1N1, A/H3N2, B/Yamagata and Victoria lineage) recommended by the WHO (World Health Organization) for quadrivalent vaccines for the respective season.
Experimental: aIIV-B Investigational aIIV-B administered as a single dose intramuscularly on Day 1Biological
Biological/Vaccine: Investigational aIIV-B Investigational MF59 Adjuvanted Quadrivalent Influenza vaccine (higher HA dose, standard dose MF59), containing four influenza virus strains (A/H1N1, A/H3N2, B/Yamagata and Victoria lineage) recommended by the WHO (World Health Organization) for quadrivalent vaccines for the respective season.
Experimental: aIIV-C Investigational aIIV-C administered as a single dose intramuscularly on Day 1Biological
Biological/Vaccine: Investigational aIIV-C Investigational MF59 Adjuvanted Quadrivalent Influenza vaccine (higher HA dose, higher dose MF59), containing four influenza virus strains (A/H1N1, A/H3N2, B/Yamagata and Victoria lineage) recommended by the WHO (World Health Organization) for quadrivalent vaccines for the respective season.
Active Comparator: Licensed IIV IIV administered as a single dose intramuscularly on Day 1Biological
Biological/Vaccine: Licensed IIV Licensed Non-adjuvanted Quadrivalent Influenza vaccine (standard HA dose), containing four influenza virus strains (A/H1N1, A/H3N2, B/Yamagata and Victoria lineage) recommended by the WHO (World Health Organization) for quadrivalent vaccines for the respective season.

Study groups in NCT05501561
Study group	Role	What they receive
IIV-A Investigational	Experimental	Not described Receives: Biological: Experimental: IIV-A Investigational IIV-A administered as a single dose intramuscularly on Day 1
aIIV-B Investigational	Experimental	Not described Receives: Biological: Experimental: aIIV-B Investigational aIIV-B administered as a single dose intramuscularly on Day 1
aIIV-C Investigational	Experimental	Not described Receives: Biological: Experimental: aIIV-C Investigational aIIV-C administered as a single dose intramuscularly on Day 1
Licensed IIV	Active comparator	Not described Receives: Biological: Active Comparator: Licensed IIV IIV administered as a single dose intramuscularly on Day 1

What is being measured

The primary outcome is the main question the study is designed to answer.

Immunogenicity Endpoint: Geometric Mean Titer (GMT): Geometric Mean of Hemagglutination Inhibition (HI) Antibodies at Day 1 and Day 29
GMTs on Day 1 (prior to vaccination) and Day 29 as determined by HI assay against each of the 4 vaccine strains.
No hypothesis testing was performed for the primary immunogenicity objectives.
Measured: Day 1 and Day 29
Immunogenicity Endpoint: Geometric Mean Fold Increase (GMFI) (HI Assay)
Geometric mean of the fold increase in serum HI titer postvaccination (Day 29) compared to prevaccination (Day 1) for each of the 4 vaccine strains.
Measured: Day 1 to Day 29
Immunogenicity Endpoint: Percentages of Subjects With HI Titers ≥1:40 at Day 1 and Day 29
Percentages of subjects with HI titers ≥1:40 at Day 1 and Day 29 for each of the 4 vaccine strains.
Measured: Day 1 and Day 29
Immunogenicity Endpoint: Percentage of Subjects With Seroconversion at Day 29 (HI Assay)
Seroconversion is defined as ≥4-fold increase in titer postvaccination in those with prevaccination titer equal to or above the lower limit of quantitation (LLOQ; 1:10), or a postvaccination titer ≥1:40 for subjects with baseline titer below the LLOQ (1:10) for HI antibodies.
Measured: Day 1 to Day 29
Immunogenicity Endpoint: GMT Ratio (HI Assay)
The GMT ratio is the geometric mean of the postvaccination HI titer for the investigational vaccine over the geometric mean of the postvaccination HI titer for the licensed IIV vaccine.
The Day 29 GMT ratios are calculated for the investigational vaccines with reference to the licensed vaccine, ie, the Day 29 GMT ratios are the ratio of the Day 29 GMTs in the Investigational group (IIV-A Investigational, aIIV-B Investigational, or aIIV-C Investigational) compared with the Day 29 GMTs in the Licensed IIV group (ie, Investigational group/Licensed IIV group). As the licensed vaccine is the reference for the GMT ratio, this parameter is presented as "1" for the Licensed IIV group (ie, Licensed IIV group/Licensed IIV group).
Measured: Day 29
Solicited Local or Systemic AEs
Number and percentage of subjects with solicited local or systemic AEs for 7 days following vaccination, based on the subject reported data (electronic Diary [eDiary]).
No hypothesis testing was performed for the primary safety objectives.
Measured: Day 1 through Day 7
Severe Solicited Local or Systemic AEs
Number and percentage of subjects with severe solicited local or systemic AEs for 7 days following vaccination, based on the subject reported data (eDiary).
Measured: Day 1 through Day 7
Unsolicited AEs
Number and percentage of subjects with unsolicited AEs for 28 days following vaccination
Measured: Day 1 to Day 29
Subjects With Serious Adverse Events (SAEs), AEs Leading to Withdrawal, Adverse Events of Special Interest (AESIs) and Medically-attended Adverse Events (MAAEs)
Number and percentage of subjects with SAEs, AEs leading to withdrawal from the study, AESIs and non-serious MAAEs
Measured: Day 1 to Day 181

Secondary outcomes (4)

Immunogenicity Endpoint: GMT: Geometric Mean of Microneutralization (MN) Antibodies Titer at Days 1 and 29
GMTs on Day 1 (prior to vaccination) and Day 29 as determined by MN assay against each of the 4 vaccine strains.
Measured: Day 1 and Day 29
Immunogenicity Endpoint: GMFI (MN Assay)
Geometric mean of the fold increase in serum MN titer postvaccination (Day 29) compared to prevaccination (Day 1) for each of the 4 vaccine strains.
Measured: Day 1 to Day 29
Immunogenicity Endpoint: Percentages of Subjects With Seroconversion at Day 29 (MN Assay)
Seroconversion is defined as ≥4-fold increase for subjects with prevaccination MN titers ≥LLOQ (1:10) or as ≥4*LLOQ (1:10) for subjects with prevaccination MN titer <LLOQ.
Measured: Day 1 to Day 29
Immunogenicity Endpoint: GMT Ratio (MN Assay)
The GMT ratio is the geometric mean of the postvaccination HI titer for the investigational vaccine over the geometric mean of the postvaccination HI titer for the licensed IIV vaccine.
The Day 29 GMT ratios are calculated for the investigational vaccines with reference to the licensed vaccine, ie, the Day 29 GMT ratios are the ratio of the Day 29 GMTs in the Investigational group (IIV-A Investigational, aIIV-B Investigational, or aIIV-C Investigational) compared with the Day 29 GMTs in the Licensed IIV group (ie, Investigational group/Licensed IIV group). As the licensed vaccine is the reference for the GMT ratio, this parameter is presented as "1" for the Licensed IIV group (ie, Licensed IIV group/Licensed IIV group).
Measured: Day 29

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

25 Aug 202231 Mar 2023

First posted15 Aug 2022
Study start25 Aug 2022
Primary completion31 Mar 2023
Study completion31 Mar 2023

Resources

Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
Posted resultsParticipant flow, outcome measures and adverse events reported by the sponsor.
Publications (1)Papers the sponsor has linked to this study.
Other trials for Influenza, HumanStudies of the same condition, open and under way.
What the trial phases meanHow a treatment moves from first tests in people to approval.

More details

For doctors and researchers: how the study is designed, who runs it, and its registry IDs.

Study design

Study type: Interventional
Phase: Phase 2
Primary purpose: Prevention
Allocation: Randomised
Intervention model: Parallel groups
Masking: Quadruple blind
Who is masked: Participant, Care provider, Investigator, Outcomes assessor
Enrolment: 1,056 participants (actual)

IDs, dates and publications

ClinicalTrials.gov ID: NCT05501561
Sponsor's protocol ID: V201_07
Status last verified: Mar 2026
First submitted: 11 Aug 2022
Last updated: 30 Jun 2026
Results posted: Yes, on ClinicalTrials.gov
Data monitoring committee: No
FDA-regulated drug: Yes
FDA-regulated device: No
Individual data sharing: Yes: SEQIRUS supports the release of anonymized subject-level and study-level data in compliance with regulatory requirements, including Clinical Documents which are part of the CTD modules submitted to regulatory agencies for public release. Summary results disclosure is either in document form (e.g., ICH E3 Clinical Study Report synopsis) or structured data form (such as summary results in ClinicalTrials.gov (United States) or eudract.ema.europa.eu (EU Clinical Trial Registry \[EU CTR\])

Publications

de Looze F, Essink BJ, van Boxmeer J, Andrade C, de Rooij R, Casula D, Xing R, Tovar MP, Albano FR. Immunogenicity and safety of higher-dose cell-based adjuvanted quadrivalent influenza vaccines: Combined results of randomised, controlled dose-finding and dose-confirmation studies. Vaccine. 2026 Apr 19;79:128436. doi: 10.1016/j.vaccine.2026.128436. Epub 2026 Mar 19.
PubMed 41855648

Want to know more?

The sponsor has not listed a contact. The official record may have more details.

Talk to your doctor first and take this page with you. Only the study team can confirm whether you can join.

Questions to ask the study team

What is the study trying to find out?
What would I need to do, and how often would I visit?
Could I receive a placebo instead of the treatment?
What are the possible risks and benefits for me?
Will it cost me anything? Are travel or time paid for?
Can I keep seeing my own doctor during the study?
What happens when the study ends?

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Study at a glance

From the registry record, last updated by the sponsor on 30 Jun 2026. Recruitment status is as the sponsor reported it: confirm with the study team.

Official title: A Phase 2b, Randomized, Observer-Blind, Antigen and Adjuvant Dose-Confirmation Clinical Study to Evaluate Safety and Immunogenicity of Different Formulations of MF59-Adjuvanted Quadrivalent Subunit Inactivated Cell-derived Influenza Vaccine (aQIVc) in Older Adults ≥50 Years of Age
ClinicalTrials.gov ID: NCT05501561
Acronym / sponsor ID: V201_07
Conditions: Influenza, Human
Keywords: influenza, vaccine, MF59, adjuvant
Phase: Phase 2
Study type: Interventional
Recruitment status: Completed
Enrolment: 1,056 participants (actual)
Lead sponsor: SeqirusIndustry (pharma, biotech, devices)
Study start: 25 Aug 2022 (actual)
Primary completion: 31 Mar 2023 (actual)
Study completion: 31 Mar 2023 (actual)
First posted: 15 Aug 2022 (actual)
Results: Posted 30 Jun 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: Quadruple blind (participant, care provider, investigator, outcomes assessor)
Number of arms: 4

Arm	Type	Receives
IIV-A Investigational	Experimental	Biological: Experimental: IIV-A Investigational IIV-A administered as a single dose intramuscularly on Day 1
aIIV-B Investigational	Experimental	Biological: Experimental: aIIV-B Investigational aIIV-B administered as a single dose intramuscularly on Day 1
aIIV-C Investigational	Experimental	Biological: Experimental: aIIV-C Investigational aIIV-C administered as a single dose intramuscularly on Day 1
Licensed IIV	Active comparator	Biological: Active Comparator: Licensed IIV IIV administered as a single dose intramuscularly on Day 1

Who may qualify

Ages: 50 years and older
Sex: All
Healthy volunteers: Accepted
Age groups: Adult, Older adult

Key inclusion criteria (6 listed)

In order to participate in this study, all subjects must meet ALL of the inclusion criteria described.
Individuals ≥50 years of age on the day of informed consent.
Individuals who have voluntarily given written consent after the nature of the study has been explained according to local regulatory requirements, prior to study entry.
Individuals who can comply with study procedures including follow-up .
Males, females of non-childbearing potential or females of childbearing potential who are using an effective birth control method, at least 30 days prior to informed consent, which they intend to use for at least 2 months after the study vaccination.

Key exclusion criteria (20 listed)

In order to participate in this study, all subjects must not meet ANY of the exclusion criteria described below:
Females of childbearing potential who are pregnant, lactating, or who have not adhered to a specified set of contraceptive methods from at least 30 days prior to informed consent and who do not plan to do so for at least 2 months after the study vaccination.
Progressive, unstable or uncontrolled clinical conditions.
Hypersensitivity, including allergy, to any component of vaccines whose use is foreseen in this study.
History of any medical condition considered an adverse event of special interest (AESI).

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

Interventions

Intervention	Type	Arms
Experimental: IIV-A Investigational IIV-A administered as a single dose intramuscularly on Day 1Biological/Vaccine: Investigational IIV-A Investigational Quadrivalent Influenza vaccine (higher hemagglutinin [HA] dose), containing four influenza virus strains (A/H1N1, A/H3N2, B/Yamagata and Victoria lineage) recommended by the WHO (World Health Organization) for quadrivalent vaccines for the respective season.	Biological	IIV-A Investigational
Experimental: aIIV-B Investigational aIIV-B administered as a single dose intramuscularly on Day 1Biological/Vaccine: Investigational aIIV-B Investigational MF59 Adjuvanted Quadrivalent Influenza vaccine (higher HA dose, standard dose MF59), containing four influenza virus strains (A/H1N1, A/H3N2, B/Yamagata and Victoria lineage) recommended by the WHO (World Health Organization) for quadrivalent vaccines for the respective season.	Biological	aIIV-B Investigational
Experimental: aIIV-C Investigational aIIV-C administered as a single dose intramuscularly on Day 1Biological/Vaccine: Investigational aIIV-C Investigational MF59 Adjuvanted Quadrivalent Influenza vaccine (higher HA dose, higher dose MF59), containing four influenza virus strains (A/H1N1, A/H3N2, B/Yamagata and Victoria lineage) recommended by the WHO (World Health Organization) for quadrivalent vaccines for the respective season.	Biological	aIIV-C Investigational
Active Comparator: Licensed IIV IIV administered as a single dose intramuscularly on Day 1Biological/Vaccine: Licensed IIV Licensed Non-adjuvanted Quadrivalent Influenza vaccine (standard HA dose), containing four influenza virus strains (A/H1N1, A/H3N2, B/Yamagata and Victoria lineage) recommended by the WHO (World Health Organization) for quadrivalent vaccines for the respective season.	Biological	Licensed IIV

Primary outcome

Immunogenicity Endpoint: Geometric Mean Titer (GMT): Geometric Mean of Hemagglutination Inhibition (HI) Antibodies at Day 1 and Day 29
Time frame: Day 1 and Day 29
GMTs on Day 1 (prior to vaccination) and Day 29 as determined by HI assay against each of the 4 vaccine strains. No hypothesis testing was performed for the primary immunogenicity objectives.
Immunogenicity Endpoint: Geometric Mean Fold Increase (GMFI) (HI Assay)
Time frame: Day 1 to Day 29
Geometric mean of the fold increase in serum HI titer postvaccination (Day 29) compared to prevaccination (Day 1) for each of the 4 vaccine strains.
Immunogenicity Endpoint: Percentages of Subjects With HI Titers ≥1:40 at Day 1 and Day 29
Time frame: Day 1 and Day 29
Percentages of subjects with HI titers ≥1:40 at Day 1 and Day 29 for each of the 4 vaccine strains.
Immunogenicity Endpoint: Percentage of Subjects With Seroconversion at Day 29 (HI Assay)
Time frame: Day 1 to Day 29
Seroconversion is defined as ≥4-fold increase in titer postvaccination in those with prevaccination titer equal to or above the lower limit of quantitation (LLOQ; 1:10), or a postvaccination titer ≥1:40 for subjects with baseline titer below the LLOQ (1:10) for HI antibodies.
Immunogenicity Endpoint: GMT Ratio (HI Assay)
Time frame: Day 29
The GMT ratio is the geometric mean of the postvaccination HI titer for the investigational vaccine over the geometric mean of the postvaccination HI titer for the licensed IIV vaccine. The Day 29 GMT ratios are calculated for the investigational vaccines with reference to the licensed vaccine, ie, the Day 29 GMT ratios are the ratio of the Day 29 GMTs in the Investigational group (IIV-A Investigational, aIIV-B Investigational, or aIIV-C Investigational) compared with the Day 29 GMTs in the Licensed IIV group (ie, Investigational group/Licensed IIV group). As the licensed vaccine is the reference for the GMT ratio, this parameter is presented as "1" for the Licensed IIV group (ie, Licensed IIV group/Licensed IIV group).
Solicited Local or Systemic AEs
Time frame: Day 1 through Day 7
Number and percentage of subjects with solicited local or systemic AEs for 7 days following vaccination, based on the subject reported data (electronic Diary [eDiary]). No hypothesis testing was performed for the primary safety objectives.
Severe Solicited Local or Systemic AEs
Time frame: Day 1 through Day 7
Number and percentage of subjects with severe solicited local or systemic AEs for 7 days following vaccination, based on the subject reported data (eDiary).
Unsolicited AEs
Time frame: Day 1 to Day 29
Number and percentage of subjects with unsolicited AEs for 28 days following vaccination
Subjects With Serious Adverse Events (SAEs), AEs Leading to Withdrawal, Adverse Events of Special Interest (AESIs) and Medically-attended Adverse Events (MAAEs)
Time frame: Day 1 to Day 181
Number and percentage of subjects with SAEs, AEs leading to withdrawal from the study, AESIs and non-serious MAAEs

4 secondary outcomes

Immunogenicity Endpoint: GMT: Geometric Mean of Microneutralization (MN) Antibodies Titer at Days 1 and 29
Time frame: Day 1 and Day 29
Immunogenicity Endpoint: GMFI (MN Assay)
Time frame: Day 1 to Day 29
Immunogenicity Endpoint: Percentages of Subjects With Seroconversion at Day 29 (MN Assay)
Time frame: Day 1 to Day 29
Immunogenicity Endpoint: GMT Ratio (MN Assay)
Time frame: Day 29

Results and safety

Results posted to the registry on 30 Jun 2026, as reported by the sponsor. Figures are copied from the record, not re-analysed. Full results on ClinicalTrials.gov.

Participant flow

Group	Started	Completed
IIV-A Investigational	264	255
aIIV-B Investigational	265	252
aIIV-C Investigational	264	253
Licensed IIV	263	254

Primary outcome: Immunogenicity Endpoint: Geometric Mean Titer (GMT): Geometric Mean of Hemagglutination Inhibition (HI) Antibodies at Day 1 and Day 29

Time frame: Day 1 and Day 29. Geometric mean (95% Confidence Interval). Unit: Geometric mean titer

Measure	IIV-A Investigational n = 256	aIIV-B Investigational n = 257	aIIV-C Investigational n = 259	Licensed IIV n = 250
A/H1N1 Day 1 HI GMT	29.79 (25.54 to 34.74)	33.09 (28.39 to 38.56)	31.78 (27.26 to 37.04)	39.29 (33.63 to 45.90)
A/H1N1 Day 29 HI GMT	286.95 (248.32 to 331.60)	302.30 (261.92 to 348.92)	369.57 (320.08 to 426.71)	198.84 (171.89 to 230.02)
A/H3N2 Day 1 HI GMT	37.81 (32.89 to 43.46)	35.11 (30.57 to 40.32)	43.33 (37.72 to 49.78)	39.80 (34.57 to 45.82)
A/H3N2 Day 29 HI GMT	140.71 (124.12 to 159.52)	149.75 (132.15 to 169.69)	171.38 (151.25 to 194.18)	133.43 (117.54 to 151.47)
B/Yamagata Day 1 HI GMT	11.18 (10.07 to 12.40)	10.49 (9.45 to 11.63)	11.08 (9.99 to 12.29)	11.03 (9.93 to 12.25)
B/Yamagata Day 29 HI GMT	35.11 (31.49 to 39.15)	38.58 (34.61 to 43.00)	51.61 (46.30 to 57.53)	31.40 (28.12 to 35.06)
B/Victoria Day 1 HI GMT	27.39 (23.77 to 31.57)	29.35 (25.48 to 33.79)	32.05 (27.83 to 36.92)	34.57 (29.94 to 39.90)
B/Victoria Day 29 HI GMT	210.22 (181.58 to 243.38)	200.86 (173.70 to 232.27)	232.61 (201.17 to 268.96)	183.28 (158.18 to 212.37)

Population analysed: Per Protocol Set, defined as all subjects in the Full Analysis Set\* who correctly received the vaccine; had no protocol deviations leading to exclusion as defined prior to unblinding/analysis; and were not excluded due to other reasons defined prior to unblinding or analysis, including subjects who withdrew informed consent prior to Day 28. \*All subjects in the All Enrolled Set who were randomized, received study vaccination and provided immunogenicity data on Day 1 and Day 29 assessment.

Primary outcome: Immunogenicity Endpoint: Geometric Mean Fold Increase (GMFI) (HI Assay)

Time frame: Day 1 to Day 29. Geometric mean (95% Confidence Interval). Unit: Geometric mean fold increase

Measure	IIV-A Investigational n = 256	aIIV-B Investigational n = 257	aIIV-C Investigational n = 259	Licensed IIV n = 250
A/H1N1 HI GMFI (Day 29/Day 1)	8.57 (7.28 to 10.08)	8.57 (7.29 to 10.08)	10.69 (9.09 to 12.57)	5.18 (4.40 to 6.11)
A/H3N2 HI GMFI (Day 29/Day 1)	3.54 (3.08 to 4.08)	3.90 (3.39 to 4.48)	4.06 (3.53 to 4.67)	3.28 (2.85 to 3.78)
B/Yamagata HI GMFI (Day 29/Day 1)	3.08 (2.75 to 3.45)	3.46 (3.09 to 3.88)	4.54 (4.05 to 5.09)	2.77 (2.46 to 3.11)
B/Victoria HI GMFI (Day 29/Day 1)	6.71 (5.72 to 7.86)	6.21 (5.31 to 7.28)	6.92 (5.91 to 8.11)	5.27 (4.49 to 6.19)

Population analysed: Per Protocol Set

Primary outcome: Immunogenicity Endpoint: Percentages of Subjects With HI Titers ≥1:40 at Day 1 and Day 29

Time frame: Day 1 and Day 29. Number (95% Confidence Interval). Unit: Percentage of participants

Measure	IIV-A Investigational n = 256	aIIV-B Investigational n = 257	aIIV-C Investigational n = 259	Licensed IIV n = 250
A/H1N1 HI titer ≥1:40 at Day 1	53.9 (47.6 to 60.1)	55.6 (49.3 to 61.8)	54.8 (48.5 to 61.0)	62.0 (55.7 to 68.0)
A/H1N1 HI titer ≥1:40 at Day 29	93.4 (89.6 to 96.1)	93.0 (89.2 to 95.8)	95.0 (91.6 to 97.3)	92.0 (87.9 to 95.0)
A/H3N2 HI titer ≥1:40 at Day 1	57.0 (50.7 to 63.2)	54.9 (48.6 to 61.1)	60.6 (54.4 to 66.6)	61.6 (55.3 to 67.7)
A/H3N2 HI titer ≥1:40 at Day 29	92.6 (88.7 to 95.5)	91.8 (87.8 to 94.9)	94.2 (90.6 to 96.7)	88.4 (83.8 to 92.1)
B/Yamagata HI titer ≥1:40 at Day 1	14.5 (10.4 to 19.4)	11.7 (8.0 to 16.2)	13.5 (9.6 to 18.3)	14.0 (9.9 to 18.9)
B/Yamagata HI titer ≥1:40 at Day 29	51.6 (45.3 to 57.8)	52.9 (46.6 to 59.2)	66.4 (60.3 to 72.1)	51.2 (44.8 to 57.5)
B/Victoria HI titer ≥1:40 at Day 1	48.8 (42.6 to 55.1)	51.8 (45.5 to 58.0)	52.9 (46.6 to 59.1)	56.8 (50.4 to 63.0)
B/Victoria HI titer ≥1:40 at Day 29	90.6 (86.4 to 93.9)	92.2 (88.2 to 95.2)	93.8 (90.2 to 96.4)	92.4 (88.4 to 95.4)

Population analysed: Per Protocol Set

Primary outcome: Immunogenicity Endpoint: Percentage of Subjects With Seroconversion at Day 29 (HI Assay)

Time frame: Day 1 to Day 29. Number (95% Confidence Interval). Unit: Percentage of participants

Measure	IIV-A Investigational n = 256	aIIV-B Investigational n = 257	aIIV-C Investigational n = 259	Licensed IIV n = 250
A/H1N1 Seroconversion at Day 29	63.3 (57.1 to 69.2)	63.0 (56.8 to 69.0)	68.7 (62.7 to 74.3)	45.2 (38.9 to 51.6)
A/H3N2 Seroconversion at Day 29	42.6 (36.4 to 48.9)	44.7 (38.6 to 51.1)	45.9 (39.8 to 52.2)	39.2 (33.1 to 45.6)
B/Yamagata Seroconversion at Day 29	28.9 (23.4 to 34.9)	36.2 (30.3 to 42.4)	44.8 (38.6 to 51.1)	25.6 (20.3 to 31.5)
B/Victoria Seroconversion at Day 29	58.6 (52.3 to 64.7)	53.7 (47.4 to 59.9)	60.2 (54.0 to 66.2)	42.8 (36.6 to 49.2)

Population analysed: Per Protocol Set

4 secondary outcomes are reported in the full results.

Adverse events

Time frame: All-Cause Mortality, SAEs, AEs leading to withdrawal from the study, AESIs and non-serious MAAEs are reported from Day 1 to Day 181; all unsolicited AEs are reported from Day 1 to Day 29. Solicited AEs are reported from Day 1 to Day 7.. Other adverse events reported at 5% frequency or more

Group	Serious adverse events	Other adverse events	Deaths
IIV-A Investigational	8 of 264 (3%)	161 of 264 (61%)	0 of 264
aIIV-B Investigational	5 of 263 (1.9%)	162 of 263 (61.6%)	0 of 263
aIIV-C Investigational	4 of 262 (1.5%)	190 of 262 (72.5%)	1 of 262
Licensed IIV	10 of 262 (3.8%)	141 of 262 (53.8%)	0 of 262

Loading the posted results from ClinicalTrials.gov…

Research links

Official record on ClinicalTrials.govLast updated by the sponsor 30 Jun 2026.
Posted resultsParticipant flow, baseline, all outcome measures and adverse events.
Derived from this study: PubMed 41855648de Looze F, Essink BJ, van Boxmeer J, Andrade C, de Rooij R, Casula D, Xing R, Tovar MP, Albano FR. Immunogenicity and safety of higher-dose cell-based adjuvanted quadrivalent influenza vaccines: Combined results of randomised, controlled dose-finding and dose-confirmation studies. Vaccine. 2026 Apr 19;79:128436. doi: 10.1016/j.vaccine.2026.128436. Epub 2026 Mar 19.
Individual participant dataSharing planned: Yes. SEQIRUS supports the release of anonymized subject-level and study-level data in compliance with regulatory requirements, including Clinical Documents which are part of the CTD modules submitted to regulatory agencies for public release. Summary results disclosure is either in document form (e.g., ICH E3 Clinical Study Report synopsis) or structured data form (such as summary results in ClinicalTrials.gov (United States) or eudract.ema.europa.eu (EU Clinical Trial Registry [EU CTR])

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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.

Clinical Program Director study director

Seqirus

47 sites in 1 country: see every site and its status.

Questions about this trial

What is this clinical trial studying?

The full registered description is in the About this study section and the official record.

Who may be eligible to take part?

The sponsor lists 6 inclusion and 20 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.

Is this clinical trial currently recruiting?

The record says: finished, as of the sponsor's last update on 30 Jun 2026. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 47 sites in United States. Whether a site is taking part right now should be confirmed with that site. See every site.

What are the possible benefits and risks?

They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.

What does this phase mean?

Phase 2 studies give the treatment to a larger group to see whether it has the intended effect and to keep checking safety.

Not every study follows the same path, and some studies (observational studies, device studies) have no phase.

Are results available for this study?

Yes. Results are posted in the registry (first posted 30 Jun 2026). A summary is in the For doctors view, and the full results are on ClinicalTrials.gov.

How can a doctor refer a patient or contact the research team?

The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

Immunogenicity Endpoint: Geometric Mean Titer (GMT): Geometric Mean of Hemagglutination Inhibition (HI) Antibodies at Day 1 and Day 29 (time frame: Day 1 and Day 29). The study lists 9 primary outcomes in all. It is what the study was designed to measure, not a finding.

Where can I read the original study information?

On the ClinicalTrials.gov record for NCT05501561, which also lists 1 linked publication.

Does a listing mean the treatment is approved or proven to work?

No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.

How often is this information updated?

AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 30 Jun 2026.