A Phase 1 interventional study of Low dose A/H2N3c + standard dose MF59 and Intermediate dose A/H2N3c + standard dose MF59 in Influenza, Human, Infections and Respiratory Tract Infections, sponsored by Seqirus. Completed at 7 sites in 2 countries. Open to participants aged 18 Years and older, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-09-21.
Sponsored by Seqirus (part of CSL Limited) · Phase 1, Interventional, and Prevention
This Phase 1, randomized, observer-blind, dose-ranging clinical study is evaluating 6 different formulations of MF59-adjuvanted and non-adjuvanted H2N3 influenza vaccine. Approximately 600 healthy adult subjects are to be randomized into 1 of 6 possible treatment groups with 100 subjects per group, stratified by age group (born after or before 1968). Each subject will receive an influenza vaccine injection on Day 1 and Day 22. Subjects will be followed up for approximately 12 months after the second vaccine injection.
The primary immunogenicity analysis is based on the Day 1, Day 8, Day 22, Day 29, and Day 43 serology data. The primary safety analysis is based on solicited local and systemic adverse events (AEs) reported within 10 days after each vaccination, unsolicited AEs reported within 3 weeks after each vaccination, and serious AEs (SAEs), medically attended AEs (MAAEs), AEs leading to withdrawal from the study, and AEs of special interest (AESIs) reported throughout the study.
2,356 studies on the registry are indexed under Influenza, Human; 184 are open to participants now.
This study's enrollment of 600 is above the median of 227 across 1,957 interventional studies indexed under Influenza, Human.
Browse Influenza, Human studies →Seqirus is the lead sponsor of 53 studies on the registry; none are open to participants now.
Of its 15 completed or terminated interventional studies of FDA-regulated products, 10 (67%) have results posted.
First submitted after Seqirus became part of CSL Limited.
Counted across the registry records on this site, refreshed daily.
Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Exclusion Criteria:
Abnormal function of the immune system resulting from:
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Able to become pregnant: from the first period until menopause, unless permanently unable to through surgery (removal of the womb, or of both ovaries or both fallopian tubes).
Criteria for people of childbearing potential usually ask for a negative pregnancy test and for contraception during the study and for a time after it.
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
An allergy, or another reaction of the immune system, to a substance. “Hypersensitivity to the study drug” means a known allergic reaction to it — not every side effect a medicine can have.
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Vaccines made with a weakened form of the germ, such as measles–mumps–rubella (MMR), chickenpox and yellow fever. They can be risky when the immune system is weakened. Flu injections are not live; the nasal flu spray is.
Informed consent
Before you join, the study team explains what taking part involves — its purpose, what happens, the risks and possible benefits — and answers your questions, so you can decide freely. Consent is usually recorded on a form (the informed consent form, ICF) signed by you or, where the law allows, by someone legally authorised to decide for you.
You can keep asking questions during the study, you are told of new information that matters, and you can choose to leave at any time.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Childbearing potential
Able to become pregnant: from the first period until menopause, unless permanently unable to through surgery (removal of the womb, or of both ovaries or both fallopian tubes).
Criteria for people of childbearing potential usually ask for a negative pregnancy test and for contraception during the study and for a time after it.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Contraception
Ways of preventing pregnancy. “Highly effective” methods fail less than 1% of the time a year when used correctly — for example an IUD or an implant.
Criteria usually say which methods count and how long to keep using them after the last dose, sometimes for male participants too. Some studies accept a partner’s vasectomy if it was confirmed successful and that person is the participant’s only sexual partner.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
BMI (body mass index)
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Hypersensitivity
An allergy, or another reaction of the immune system, to a substance. “Hypersensitivity to the study drug” means a known allergic reaction to it — not every side effect a medicine can have.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Contraindication
A reason a treatment, test or procedure should not be given to a particular person, such as an allergy, another illness or a medicine they take.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Corticosteroids (steroids)
Anti-inflammatory medicines such as prednisone, prednisolone and dexamethasone — not the anabolic steroids used for muscle.
Studies differ in what they allow: check which steroid medicines, routes (tablets, injections, creams, inhalers, eye drops) and doses this study accepts.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Investigational drug or device
A drug or device being studied in a clinical trial.
It may be new, or already approved and being studied for another use, dose or form. Criteria often leave out people who took part in another study of one within a recent period, commonly 30 days or five half-lives.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Live vaccines
Vaccines made with a weakened form of the germ, such as measles–mumps–rubella (MMR), chickenpox and yellow fever. They can be risky when the immune system is weakened. Flu injections are not live; the nasal flu spray is.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Eligible subjects who have been randomized to receive two intramuscular vaccinations (3 weeks apart) of low dose A/H2N3c + standard dose MF59 adjuvant
Biological: Low dose A/H2N3c + standard dose MF59
Eligible subjects who have been randomized to receive two intramuscular vaccinations (3 weeks apart) of intermediate dose A/H2N3c + standard dose MF59 adjuvant
Biological: Intermediate dose A/H2N3c + standard dose MF59
Eligible subjects who have been randomized to receive two intramuscular vaccinations (3 weeks apart) of high dose A/H2N3c + standard dose MF59 adjuvant
Biological: High dose A/H2N3c + standard dose MF59
Eligible subjects who have been randomized to receive two intramuscular vaccinations (3 weeks apart) of high dose A/H2N3c non-adjuvanted
Biological: High dose A/H2N3c non-adjuvanted
Eligible subjects who have been randomized to receive two intramuscular vaccinations (3 weeks apart) of lowest dose A/H2N3c + high dose MF59 adjuvant
Biological: Lowest dose A/H2N3c + high dose MF59
Eligible subjects who have been randomized to receive two intramuscular vaccinations (3 weeks apart) of low dose A/H2N3c + high dose MF59 adjuvant
Biological: Low dose A/H2N3c + high dose MF59
Two intramuscular injections (3 weeks apart) of cell culture-derived MF59 adjuvanted H2N3 vaccine
Two intramuscular injections (3 weeks apart) of cell culture-derived MF59 adjuvanted H2N3 vaccine
Two intramuscular injections (3 weeks apart) of cell culture-derived MF59 adjuvanted H2N3 vaccine
Two intramuscular injections (3 weeks apart) of cell culture-derived non-adjuvanted H2N3 vaccine
Two intramuscular injections (3 weeks apart) of cell culture-derived MF59 adjuvanted H2N3 vaccine
Two intramuscular injections (3 weeks apart) of cell culture-derived MF59 adjuvanted H2N3 vaccine
Geometric mean titer (GMT) of hemagglutination inhibition (HI) antibodies against homologous H2N3 strain - Day 1
GMT (HI) prevaccination
Time frame: Day 1
GMT of HI antibodies against homologous H2N3 strain - Day 8
GMT (HI) 1 week postvaccination 1
Time frame: Day 8
GMT of HI antibodies against homologous H2N3 strain Day 22
GMT (HI) 3 weeks postvaccination 1
Time frame: Day 22
GMT of HI antibodies against homologous H2N3 strain - Day 29
GMT (HI) 1 week postvaccination 2
Time frame: Day 29
GMT of HI antibodies against homologous H2N3 strain - Day 43
GMT (HI) 3 weeks postvaccination 2
Time frame: Day 43
GMT of microneutralization (MN) antibodies against homologous H2N3 strain - Day 1
GMT (MN) prevaccination
Time frame: Day 1
GMT of MN antibodies against homologous H2N3 strain - Day 8
GMT (MN) 1 week postvaccination 1
Time frame: Day 8
GMT of MN antibodies against homologous H2N3 strain - Day 22
GMT (MN) 3 weeks postvaccination 1
Time frame: Day 22
GMT of MN antibodies against homologous H2N3 strain - Day 29
GMT (MN) 1 week postvaccination 2
Time frame: Day 29
GMT of MN antibodies against homologous H2N3 strain - Day 43
GMT (MN) 3 weeks postvaccination 2
Time frame: Day 43
Geometric mean fold increase (GMFI) of HI antibodies against homologous H2N3 strain - Day 8
GMFI (HI) 1 week postvaccination 1 compared to prevaccination
Time frame: Day 8
GMFI of HI antibodies against homologous H2N3 strain - Day 22
GMFI (HI) 3 weeks postvaccination 1 compared to prevaccination
Time frame: Day 22
GMFI of HI antibodies against homologous H2N3 strain - Day 29
GMFI (HI) 1 week postvaccination 2 compared to prevaccination
Time frame: Day 29
GMFI of HI antibodies against homologous H2N3 strain - Day 43
GMFI (HI) 3 weeks postvaccination 2 compared to prevaccination
Time frame: Day 43
GMFI of MN antibodies against homologous H2N3 strain - Day 8
GMFI (MN) 1 week postvaccination 1 compared to prevaccination
Time frame: Day 8
GMFI of MN antibodies against homologous H2N3 strain - Day 22
GMFI (MN) 3 weeks postvaccination 1 compared to prevaccination
Time frame: Day 22
GMFI of MN antibodies against homologous H2N3 strain - Day 29
GMFI (MN) 1 week postvaccination 2 compared to prevaccination
Time frame: Day 29
GMFI of MN antibodies against homologous H2N3 strain - Day 43
GMFI (MN) 3 weeks postvaccination 2 compared to prevaccination
Time frame: Day 43
Percentages of subjects with HI titers ≥1:40 against homologous H2N3 strain - Day 1
% ≥1:40 (HI) prevaccination
Time frame: Day 1
Percentages of subjects with HI titers ≥1:40 against homologous H2N3 strain - Day 8
% ≥1:40 (HI) 1 week postvaccination 1
Time frame: Day 8
Percentages of subjects with HI titers ≥1:40 against homologous H2N3 strain - Day 22
% ≥1:40 (HI) 3 weeks postvaccination 1
Time frame: Day 22
Percentages of subjects with HI titers ≥1:40 against homologous H2N3 strain - Day 29
% ≥1:40 (HI) 1 week postvaccination 2
Time frame: Day 29
Percentages of subjects with HI titers ≥1:40 against homologous H2N3 strain - Day 43
% ≥1:40 (HI) 3 weeks postvaccination 2
Time frame: Day 43
Percentages of subjects with MN titers ≥1:40 against homologous H2N3 strain - Day 1
% ≥1:40 (MN) prevaccination
Time frame: Day 1
Percentages of subjects with MN titers ≥1:40 against homologous H2N3 strain - Day 8
% ≥1:40 (MN) 1 week postvaccination 1
Time frame: Day 8
Percentages of subjects with MN titers ≥1:40 against homologous H2N3 strain - Day 22
% ≥1:40 (MN) 3 weeks postvaccination 1
Time frame: Day 22
Percentages of subjects with MN titers ≥1:40 against homologous H2N3 strain - Day 29
% ≥1:40 (MN) 1 week postvaccination 2
Time frame: Day 29
Percentages of subjects with MN titers ≥1:40 against homologous H2N3 strain - Day 43
% ≥1:40 (MN) 3 weeks postvaccination 2
Time frame: Day 43
Percentages of subjects with seroconversion by HI against homologous H2N3 strain - Day 8
% seroconversion (HI) 1 week postvaccination 1, defined as a ≥4-fold increase in HI titer postvaccination in those with prevaccination titer ≥1:10, or a postvaccination HI titer ≥1:40 for subjects with baseline titer \<1:10
Time frame: Day 8
Percentages of subjects with seroconversion by HI against homologous H2N3 strain - Day 22
% seroconversion (HI) 3 weeks postvaccination 1, defined as a ≥4-fold increase in HI titer postvaccination in those with prevaccination titer ≥1:10, or a postvaccination HI titer ≥1:40 for subjects with baseline titer \<1:10
Time frame: Day 22
Percentages of subjects with seroconversion by HI against homologous H2N3 strain - Day 29
% seroconversion (HI) 1 week postvaccination 2, defined as a ≥4-fold increase in HI titer postvaccination in those with prevaccination titer ≥1:10, or a postvaccination HI titer ≥1:40 for subjects with baseline titer \<1:10
Time frame: Day 29
Percentages of subjects with seroconversion by HI against homologous H2N3 strain - Day 43
% seroconversion (HI) 3 weeks postvaccination 2, defined as a ≥4-fold increase in HI titer postvaccination in those with prevaccination titer ≥1:10, or a postvaccination HI titer ≥1:40 for subjects with baseline titer \<1:10
Time frame: Day 43
Percentages of subjects with seroconversion by MN against homologous H2N3 strain - Day 8
% seroconversion (MN) 1 week postvaccination 1, defined as a ≥4-fold increase in MN titer postvaccination in those with prevaccination titer ≥lower limit of quantification (LLOQ), or a postvaccination MN titer ≥4×LLOQ for subjects with baseline titer \<LLOQ
Time frame: Day 8
Percentages of subjects with seroconversion by MN against homologous H2N3 strain - Day 22
% seroconversion (MN) 3 weeks postvaccination 1, defined as a ≥4-fold increase in MN titer postvaccination in those with prevaccination titer ≥lower limit of quantification (LLOQ), or a postvaccination MN titer ≥4×LLOQ for subjects with baseline titer \<LLOQ
Time frame: Day 22
Percentages of subjects with seroconversion by MN against homologous H2N3 strain - Day 29
% seroconversion (MN) 1 week postvaccination 2, defined as a ≥4-fold increase in MN titer postvaccination in those with prevaccination titer ≥lower limit of quantification (LLOQ), or a postvaccination MN titer ≥4×LLOQ for subjects with baseline titer \<LLOQ
Time frame: Day 29
Percentages of subjects with seroconversion by MN against homologous H2N3 strain - Day 43
% seroconversion (MN) 3 weeks postvaccination 2, defined as a ≥4-fold increase in MN titer postvaccination in those with prevaccination titer ≥lower limit of quantification (LLOQ), or a postvaccination MN titer ≥4×LLOQ for subjects with baseline titer \<LLOQ
Time frame: Day 43
Number and percentages of subjects reporting solicited local and systemic adverse events (AEs) - Day 1 through Day 10
10 consecutive days postvaccination 1
Time frame: Day 1 through Day 10
Number and percentages of subjects reporting solicited local and systemic AEs - Day 22 through Day 31
10 consecutive days postvaccination 2
Time frame: Day 22 through Day 31
Number and percentage of subjects reporting any unsolicited AEs
For 3 weeks following each vaccination
Time frame: Day 1 through Day 43
Number and percentage of subjects reporting serious AEs (SAEs), AEs leading to withdrawal, AEs of special interest (AESI) and medically attended AEs (MAAEs)
From vaccination until study completion
Time frame: Day 1 through Day 387
GMT of ELLA titers as a measure of anti-neuraminidase (NA) immunogenicity
GMT (ELLA) prevaccination, 1 and 3 weeks postvaccination
Time frame: Day 1, Day 8, Day 22, Day 29, Day 43
GMFI of ELLA titers as a measure of anti-NA immunogenicity
GMFI (ELLA) 1 and 3 weeks postvaccination compared to prevaccination
Time frame: Day 8, Day 22, Day 29, Day 43
Percentage of subjects with ≥4-fold increase in ELLA titer as a measure of anti-NA immunogenicity
% ≥4-fold increase (ELLA) 1 and 3 weeks postvaccination compared to prevaccination
Time frame: Day 8, Day 22, Day 29, Day 43
GMT of HI antibodies against homologous H2N3 strain - Persistence
GMT (HI) 6 and 12 months postvaccination 2
Time frame: Day 202, Day 387
GMT of MN antibodies against homologous H2N3 strain - Persistence
GMT (MN) 6 and 12 months postvaccination 2
Time frame: Day 202, Day 387
GMT of ELLA titer as a measure of anti-NA immunogenicity- Persistence
GMT (ELLA) 6 and 12 months postvaccination 2
Time frame: Day 202, Day 387
GMFI of HI antibodies against homologous H2N3 strain - Persistence
GMFI (HI) 6 and 12 months postvaccination 2 compared to prevaccination
Time frame: Day 202, Day 387
GMFI of MN antibodies against homologous H2N3 strain - Persistence
GMFI (MN) 6 and 12 months postvaccination 2 compared to prevaccination
Time frame: Day 202, Day 387
GMFI of ELLA titer as a measure of anti-NA immunogenicity- Persistence
GMFI (ELLA) 6 and 12 months postvaccination 2 compared to prevaccination
Time frame: Day 202, Day 387
Percentages of subjects with HI titers ≥1:40 against homologous H2N3 strain - Persistence
% ≥1:40 (HI) 6 and 12 months postvaccination 2
Time frame: Day 202, Day 387
Percentages of subjects with MN titers ≥1:40, ≥1:80 and ≥1:160 against homologous H2N3 strain - Persistence
% ≥1:40, ≥1:80 and ≥1:160 (MN) 6 and 12 months postvaccination 2
Time frame: Day 202, Day 387
Percentages of subjects with seroconversion by HI against homologous H2N3 strain - Persistence
% seroconversion (HI) 6 and 12 months postvaccination 2, defined as a ≥4-fold increase in HI titer postvaccination in those with prevaccination titer ≥1:10, or a postvaccination HI titer ≥1:40 for subjects with baseline titer \<1:10
Time frame: Day 202, Day 387
Percentages of subjects with seroconversion by MN against homologous H2N3 strain - Persistence
% seroconversion (MN) 6 and 12 months postvaccination 2, defined as a ≥4-fold increase in MN titer postvaccination in those with prevaccination titer ≥LLOQ, or a postvaccination MN titer ≥4×LLOQ for subjects with baseline titer \<LLOQ
Time frame: Day 202, Day 387
Percentage of subjects with ≥4-fold increase in ELLA titer as a measure of anti-NA immunogenicity - Persistence
% ≥4-fold increase (ELLA) 6 and 12 months postvaccination 2 compared to prevaccination
Time frame: Day 202, Day 387
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