Influenza, HumanPhase 2NCT05422326

A Study to Evaluate Safety and Immunogenicity of One or Two Booster Vaccinations With H5N6 Influenza Vaccine in Adults Primed With H5N1 Influenza Vaccine or Unprimed

A Phase 2 study testing aH5N6c on Day 1 and aH5N6c on Day 22 in people with Influenza, Human and Influenza in Birds, run by Seqirus at 18 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 18 years and olderHealthy volunteers can take part
Conditions the study is for: Influenza, Human, Influenza in Birds, Respiratory Tract Infections
What is being tested?: aH5N6c on Day 1 and aH5N6c on Day 22
Type of treatment: Vaccines, Injection or infusion
Could I receive a placebo?: Yes, some participants may receive a placebo
How many people: 260 participants
Where: 18 sitesUnited States
Study dates: 18 Jul 2022to 24 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 18 years and older
All sexes
Healthy volunteers accepted
Adult, Older adult

Who may be able to join

Subjects who received 2 doses of aH5N1c vaccine or placebo in and completed the parent study V89_18 in the <65 years of age cohort.
Individuals who can comply with study procedures including follow-up.

Who cannot join

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 study entry and who do not plan to do so until at least 30 days after the last study vaccination.
Progressive, unstable or uncontrolled clinical conditions.
Hypersensitivity, including allergy, to any component of vaccines, medicinal products or medical equipment whose use is foreseen in this study.
Clinical conditions representing a contraindication to intramuscular vaccination and blood draws.
Abnormal function of the immune system.
History of any medical condition considered an adverse event of special interest (AESI).

Show all 13Show fewer

Received immunoglobulins with immunomodulating effects or any blood products within 180 days prior to informed consent.
Subjects, who received an influenza H5 vaccine other than in the V89_18 parent study or have a history of H5 influenza infection prior to enrollment.
Received an investigational or non-registered medicinal product within 30 days prior to informed consent.
Individuals who received any other vaccines [except corona virus disease 2019 (COVID-19) vaccines] within 14 days (for inactivated vaccines) or 28 days (for live vaccines) prior to enrollment in this study or who are planning to receive any vaccine within 28 days from the study vaccination.
Receipt of any COVID-19 vaccine within 7 days prior to enrollment or plan to receive any COVID-19 vaccine within 7 days from study vaccination.
Acute (severe) febrile illness.
A known history of Guillain-Barre Syndrome or other demyelinating diseases such as encephalomyelitis and transverse myelitis.

Trial locations and contacts

18 sites in 1 country.

City, postcode or hospital

18 sites in 1 country

United States18 sites

Great Lakes Clinical Trials LLC
Chicago, Illinois, 60640
Innovative Research of West Florida, Inc.
Clearwater, Florida, 33756
Aventiv Research
Columbus, Ohio, 43213
Optimal Research, LLC
Huntsville, Alabama, 35802
The Center for Pharmaceutical Research
Kansas City, Missouri, 64114
Optimal Research, LLC
Melbourne, Florida, 32934
Clinical Research Consulting, LLC
Milford, Connecticut, 06460
PMG Research of Raleigh
Raleigh, North Carolina, 27609
Rochester Clinical Research, Inc
Rochester, New York, 14609
J. Lewis Research, Inc/Foothill Family Clinic North
Salt Lake City, Utah, 84109
J. Lewis Research, Inc/Foothill Family Clinic South
Salt Lake City, Utah, 84121
Biogenics Research Institute
San Antonio, Texas, 78229
California Research Foundation
San Diego, California, 92103
J. Lewis Research, Inc/Jordan River Family Medicine
South Jordan, Utah, 84095
Sundance Clinical Research, LLC
St Louis, Missouri, 63141
Clinical Research Consortium Arizona
Tempe, Arizona, 85283
Heartland Research Associates, LLC
Wichita, Kansas, 67207
AccellaCare
Winston-Salem, North Carolina, 27103

Other trials in United States

About this study

Official title: A Phase 2, Randomized, Study to Evaluate Safety and Immunogenicity of One or Two Heterologous Booster Vaccinations With an MF59-adjuvanted, Cell Culture-derived H5N6 Influenza Vaccine in Adults Primed With MF59-adjuvanted, Cell Culture-derived H5N1 Influenza Vaccine or Unprimed

This is a Phase 2, randomized, multi-center study in approximately 300 adults who received 2 doses of aH5N1c or placebo in and completed the parent study V89_18 in the <65 years of age cohort. The study investigates whether two priming doses of MF59-adjuvanted H5N1 cell culture-derived vaccine (aH5N1c) followed by one or two booster vaccinations with a MF59-adjuvanted H5N6 cell culture derived vaccine (aH5N6c) 3 weeks apart elicit immune responses to the antigens used for priming (H5N1) and boosting (H5N6) after first and second heterologous booster vaccination.

Eligible subjects, who received 2 doses of aH5N1c in the parent study V89_18 are randomized in a 1:1 ratio to receive either two aH5N6c vaccinations, 3 weeks apart (group 1) or an aH5N6c vaccination on Day 1 and saline placebo on Day 22 (group 2). Eligible subjects, who received placebo in the parent study will receive two aH5N6c vaccinations, 3 weeks apart (group 3). After the second vaccine administration, subjects are monitored for approximately 6 months for safety and antibody persistence. The total study duration will be approximately 7 months per subject.

Conditions: Influenza, Human, Influenza in Birds, Respiratory Tract Infections, Infections, Orthomyxoviridae Infections, RNA Virus Infections
Being tested: aH5N6c on Day 1, aH5N6c on Day 22, Placebo on Day 22
Keywords: Influenza, Pandemic, Vaccine, H5N1, H5N6, Flu, MF59, Avian
Medical subject headings: Influenza, Human, Influenza in Birds, Respiratory Tract Infections, Infections, Orthomyxoviridae Infections, RNA Virus Infections, Virus Diseases, Respiratory Tract Diseases

What participants receive

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

aH5N6c on Day 1Biological
MF59-adjuvanted cell-culture derived subunit inactivated monovalent A/H5N6 vaccine (aH5N6c) for intramuscular (IM) administration, containing 7.5 μg H5N6 hemagglutinin (HA) (A/Guangdong/18SF020/2018 (H5N6)-like) + 0.25 mL MF59 (approximately 0.5 mL total volume)
aH5N6c on Day 22Biological
MF59-adjuvanted cell-culture derived subunit inactivated monovalent A/H5N6 vaccine (aH5N6c) for intramuscular (IM) administration, containing 7.5 μg H5N6 HA (A/Guangdong/18SF020/2018 (H5N6)-like) + 0.25 mL MF59 (approximately 0.5 mL total volume) given 3 weeks after the first aH5N6c vaccination
Placebo on Day 22Biological
Saline placebo (sterile, 0.5 mL) given 3 weeks after the aH5N6c vaccination

Study groups in NCT05422326
Study group	Role	What they receive
Group 1	Experimental	Eligible subjects who received 2 doses of aH5N1c in the parent study V89_18 and have been randomized to receive two aH5N6c vaccinations, 3 weeks apart Receives: Biological: aH5N6c on Day 1; Biological: aH5N6c on Day 22
Group 2	Experimental	Eligible subjects who received 2 doses of aH5N1c in the parent study V89_18 and have been randomized to receive an aH5N6c vaccination on Day 1 and saline placebo on Day 22 Receives: Biological: aH5N6c on Day 1; Biological: Placebo on Day 22
Group 3	Experimental	Eligible subjects who received placebo in the parent study V89_18 receive two aH5N6c vaccinations, 3 weeks apart. Receives: Biological: aH5N6c on Day 1; Biological: aH5N6c on Day 22

What is being measured

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

Geometric Mean Titer (GMT) of Hemagglutination Inhibition (HI) Antibodies Against the H5N6 Strain
GMT pre-vaccination, 1 and 3 weeks post-vaccination 1, and 3 weeks post-vaccination 2
Note: The Overall Number of Participants Analyzed (N) represents the total number of participants in the per-protocol set (PPS); definitions are provided in the Statistical Analysis Plan (SAP). The Number Analyzed (n) at each timepoint corresponds to the number of participants with an available serum analysis result for the relevant strain at that timepoint. Instances where n<N reflect missing serum samples or non-evaluable results. All participants included in the Overall Number of Participants Analyzed contributed data to the analysis at one or more timepoints.
Measured: Day 1, Day 8, Day 22, Day 43
Geometric Mean Fold Increase (GMFI) of HI Antibodies Against the H5N6 Strain
GMFI 1 and 3 weeks post-vaccination 1, and 3 weeks post-vaccination 2 compared to pre-vaccination (Day 1)
Note: The Overall Number of Participants Analyzed (N) represents the total number of participants in the PPS; definitions are provided in the SAP. The Number Analyzed (n) at each timepoint corresponds to the number of participants with an available serum analysis result for the relevant strain at that timepoint. Instances where n<N reflect missing serum samples or non-evaluable results. All participants included in the Overall Number of Participants Analyzed contributed data to the analysis at one or more timepoints.
Measured: Day 1, Day 8, Day 22, Day 43
Percentage of Subjects With HI Titers ≥1:40 Against the H5N6 Strain
Pre-vaccination, 1 and 3 weeks post-vaccination 1, and 3 weeks post-vaccination 2
Note: The Overall Number of Participants Analyzed (N) represents the total number of participants in the PPS; definitions are provided in the SAP. The Number Analyzed (n) at each timepoint corresponds to the number of participants with an available serum analysis result for the relevant strain at that timepoint. Instances where n<N reflect missing serum samples or non-evaluable results. All participants included in the Overall Number of Participants Analyzed contributed data to the analysis at one or more timepoints.
Measured: Day 1, Day 8, Day 22, Day 43
Percentage of Subjects With Seroconversion Against the H5N6 Strain
Seroconversion 1 and 3 weeks post-vaccination 1, and 3 weeks post-vaccination 2, defined as a ≥4-fold increase in HI titer post-vaccination in those with pre-vaccination titer ≥1:10, or a post-vaccination HI titer ≥1:40 for subjects with baseline titer <1:10
Note: The Overall Number of Participants Analyzed (N) represents the total number of participants in the PPS; definitions are provided in the SAP. The Number Analyzed (n) at each timepoint corresponds to the number of participants with an available serum analysis result for the relevant strain at that timepoint. Instances where n<N reflect missing serum samples or non-evaluable results. All participants included in the Overall Number of Participants Analyzed contributed data to the analysis at one or more timepoints.
Measured: Day 8, Day 22, Day 43

Secondary outcomes (11)

GMT of HI Antibodies Against the H5N1 Strain
GMT pre-vaccination, 1 and 3 weeks post-vaccination 1, and 3 weeks and 6 months post-vaccination 2
Note: The Overall Number of Participants Analyzed (N) represents the total number of participants in the PPS; definitions are provided in the SAP. The Number Analyzed (n) at each timepoint corresponds to the number of participants with an available serum analysis result for the relevant strain at that timepoint. Instances where n<N reflect missing serum samples or non-evaluable results. All participants included in the Overall Number of Participants Analyzed contributed data to the analysis at one or more timepoints.
Measured: Day 1, Day 8, Day 22, Day 43, Day 202
GMFI of HI Antibodies Against the H5N1 Strain
GMFI 1 and 3 weeks post-vaccination 1, and 3 weeks and 6 months post-vaccination 2 compared to pre-vaccination (Day 1)
Note: The Overall Number of Participants Analyzed (N) represents the total number of participants in the PPS; definitions are provided in the SAP. The Number Analyzed (n) at each timepoint corresponds to the number of participants with an available serum analysis result for the relevant strain at that timepoint. Instances where n<N reflect missing serum samples or non-evaluable results. All participants included in the Overall Number of Participants Analyzed contributed data to the analysis at one or more timepoints.
Measured: Day 1, Day 8, Day 22, Day 43, Day 202
Percentage of Subjects With HI Titers ≥1:40 Against the H5N1 Strain
Pre-vaccination, 1 and 3 weeks post-vaccination 1, and 3 weeks and 6 months post-vaccination 2
Note: The Overall Number of Participants Analyzed (N) represents the total number of participants in the PPS; definitions are provided in the SAP. The Number Analyzed (n) at each timepoint corresponds to the number of participants with an available serum analysis result for the relevant strain at that timepoint. Instances where n<N reflect missing serum samples or non-evaluable results. All participants included in the Overall Number of Participants Analyzed contributed data to the analysis at one or more timepoints.
Measured: Day 1, Day 8, Day 22, Day 43, Day 202
Percentage of Subjects With Seroconversion Against the H5N1 Strain
Seroconversion 1 and 3 weeks post-vaccination 1, and 3 weeks and 6 months post-vaccination 2, defined as a ≥4-fold increase in HI titer post-vaccination in those with pre-vaccination titer ≥1:10, or a post-vaccination HI titer ≥1:40 for subjects with baseline titer <1:10
Note: The Overall Number of Participants Analyzed (N) represents the total number of participants in the PPS; definitions are provided in the SAP. The Number Analyzed (n) at each timepoint corresponds to the number of participants with an available serum analysis result for the relevant strain at that timepoint. Instances where n<N reflect missing serum samples or non-evaluable results. All participants included in the Overall Number of Participants Analyzed contributed data to the analysis at one or more timepoints.
Measured: Day 8, Day 22, Day 43, Day 202
GMT of HI Antibodies Against the H5N6 Strain
GMT 6 months post-vaccination 2
Measured: Day 202
GMFI of HI Antibodies Against the H5N6 Strain
GMFI 6 months post-vaccination 2 compared to pre-vaccination (Day 1)
Measured: Day 1, Day 202
Percentage of Subjects With HI Titers ≥1:40 Against the H5N6 Strain
6 months post-vaccination 2
Measured: Day 202
Percentage of Subjects With Seroconversion Against the H5N6 Strain
Seroconversion 6 months post-vaccination 2, defined as a ≥4-fold increase in HI titer post-vaccination in those with pre-vaccination titer ≥1:10, or a post-vaccination HI titer ≥1:40 for subjects with baseline titer <1:10
Measured: Day 202
Frequency and Severity of Solicited Local and Systemic Adverse Events (AEs)
For 7 days following each vaccination
Measured: Day 1 through Day 7 and Day 22 through Day 28
Frequency and Severity of Unsolicited AEs
For 3 weeks following each vaccination
Measured: Day 1 through Day 43
Frequency of Serious AEs (SAEs), AEs Leading to Withdrawal, AEs of Special Interest (AESI) and Medically Attended AEs (MAAEs)
From vaccination until study completion
Measured: Day 1 through Day 202

Timeline

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

18 Jul 202224 Mar 2023

First posted16 Jun 2022
Study start18 Jul 2022
Primary completion24 Oct 2022
Study completion24 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.
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
Model description: Eligible subjects, who received 2 doses of aH5N1c in the parent study V89\_18 are randomized in a 1:1 ratio to group 1 (two aH5N6c vaccinations, 3 weeks apart) or group 2 (aH5N6c vaccination and placebo, 3 weeks apart). Eligible subjects, who received placebo in the parent study are allocated to group 3 (two aH5N6c vaccinations, 3 weeks apart).
Masking: Triple blind
Who is masked: Participant, Investigator, Outcomes assessor
Enrolment: 260 participants (actual)

IDs, dates and publications

ClinicalTrials.gov ID: NCT05422326
Sponsor's protocol ID: V89_18E1
Status last verified: Oct 2025
First submitted: 14 Jun 2022
Last updated: 13 May 2026
Results posted: Yes, on ClinicalTrials.gov
Data monitoring committee: No
FDA-regulated drug: Yes
FDA-regulated device: No
Individual data sharing: Undecided

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 13 May 2026. Recruitment status is as the sponsor reported it: confirm with the study team.

Official title: A Phase 2, Randomized, Study to Evaluate Safety and Immunogenicity of One or Two Heterologous Booster Vaccinations With an MF59-adjuvanted, Cell Culture-derived H5N6 Influenza Vaccine in Adults Primed With MF59-adjuvanted, Cell Culture-derived H5N1 Influenza Vaccine or Unprimed
ClinicalTrials.gov ID: NCT05422326
Acronym / sponsor ID: V89_18E1
Conditions: Influenza, Human, Influenza in Birds, Respiratory Tract Infections, Infections, Orthomyxoviridae Infections, RNA Virus Infections
Keywords: Influenza, Pandemic, Vaccine, H5N1, H5N6, Flu, MF59, Avian
Phase: Phase 2
Study type: Interventional
Recruitment status: Completed
Enrolment: 260 participants (actual)
Lead sponsor: SeqirusIndustry (pharma, biotech, devices)
Study start: 18 Jul 2022 (actual)
Primary completion: 24 Oct 2022 (actual)
Study completion: 24 Mar 2023 (actual)
First posted: 16 Jun 2022 (actual)
Results: Posted 13 May 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: 3
Model description: Eligible subjects, who received 2 doses of aH5N1c in the parent study V89_18 are randomized in a 1:1 ratio to group 1 (two aH5N6c vaccinations, 3 weeks apart) or group 2 (aH5N6c vaccination and placebo, 3 weeks apart). Eligible subjects, who received placebo in the parent study are allocated to group 3 (two aH5N6c vaccinations, 3 weeks apart).

Arm	Type	Receives
Group 1	Experimental	Biological: aH5N6c on Day 1, Biological: aH5N6c on Day 22Eligible subjects who received 2 doses of aH5N1c in the parent study V89_18 and have been randomized to receive two aH5N6c vaccinations, 3 weeks apart
Group 2	Experimental	Biological: aH5N6c on Day 1, Biological: Placebo on Day 22Eligible subjects who received 2 doses of aH5N1c in the parent study V89_18 and have been randomized to receive an aH5N6c vaccination on Day 1 and saline placebo on Day 22
Group 3	Experimental	Biological: aH5N6c on Day 1, Biological: aH5N6c on Day 22Eligible subjects who received placebo in the parent study V89_18 receive two aH5N6c vaccinations, 3 weeks apart.

Who may qualify

Ages: 18 years and older
Sex: All
Healthy volunteers: Accepted
Age groups: Adult, Older adult

Key inclusion criteria (2 listed)

Subjects who received 2 doses of aH5N1c vaccine or placebo in and completed the parent study V89_18 in the <65 years of age cohort.
Individuals who can comply with study procedures including follow-up.

Key exclusion criteria (13 listed)

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 study entry and who do not plan to do so until at least 30 days after the last study vaccination.
Progressive, unstable or uncontrolled clinical conditions.
Hypersensitivity, including allergy, to any component of vaccines, medicinal products or medical equipment whose use is foreseen in this study.
Clinical conditions representing a contraindication to intramuscular vaccination and blood draws.
Abnormal function of the immune system.

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
aH5N6c on Day 1MF59-adjuvanted cell-culture derived subunit inactivated monovalent A/H5N6 vaccine (aH5N6c) for intramuscular (IM) administration, containing 7.5 μg H5N6 hemagglutinin (HA) (A/Guangdong/18SF020/2018 (H5N6)-like) + 0.25 mL MF59 (approximately 0.5 mL total volume)	Biological	Group 1, Group 2, Group 3
aH5N6c on Day 22MF59-adjuvanted cell-culture derived subunit inactivated monovalent A/H5N6 vaccine (aH5N6c) for intramuscular (IM) administration, containing 7.5 μg H5N6 HA (A/Guangdong/18SF020/2018 (H5N6)-like) + 0.25 mL MF59 (approximately 0.5 mL total volume) given 3 weeks after the first aH5N6c vaccination	Biological	Group 1, Group 3
Placebo on Day 22Saline placebo (sterile, 0.5 mL) given 3 weeks after the aH5N6c vaccination	Biological	Group 2

Primary outcome

Geometric Mean Titer (GMT) of Hemagglutination Inhibition (HI) Antibodies Against the H5N6 Strain
Time frame: Day 1, Day 8, Day 22, Day 43
GMT pre-vaccination, 1 and 3 weeks post-vaccination 1, and 3 weeks post-vaccination 2 Note: The Overall Number of Participants Analyzed (N) represents the total number of participants in the per-protocol set (PPS); definitions are provided in the Statistical Analysis Plan (SAP). The Number Analyzed (n) at each timepoint corresponds to the number of participants with an available serum analysis result for the relevant strain at that timepoint. Instances where n<N reflect missing serum samples or non-evaluable results. All participants included in the Overall Number of Participants Analyzed contributed data to the analysis at one or more timepoints.
Geometric Mean Fold Increase (GMFI) of HI Antibodies Against the H5N6 Strain
Time frame: Day 1, Day 8, Day 22, Day 43
GMFI 1 and 3 weeks post-vaccination 1, and 3 weeks post-vaccination 2 compared to pre-vaccination (Day 1) Note: The Overall Number of Participants Analyzed (N) represents the total number of participants in the PPS; definitions are provided in the SAP. The Number Analyzed (n) at each timepoint corresponds to the number of participants with an available serum analysis result for the relevant strain at that timepoint. Instances where n<N reflect missing serum samples or non-evaluable results. All participants included in the Overall Number of Participants Analyzed contributed data to the analysis at one or more timepoints.
Percentage of Subjects With HI Titers ≥1:40 Against the H5N6 Strain
Time frame: Day 1, Day 8, Day 22, Day 43
Pre-vaccination, 1 and 3 weeks post-vaccination 1, and 3 weeks post-vaccination 2 Note: The Overall Number of Participants Analyzed (N) represents the total number of participants in the PPS; definitions are provided in the SAP. The Number Analyzed (n) at each timepoint corresponds to the number of participants with an available serum analysis result for the relevant strain at that timepoint. Instances where n<N reflect missing serum samples or non-evaluable results. All participants included in the Overall Number of Participants Analyzed contributed data to the analysis at one or more timepoints.
Percentage of Subjects With Seroconversion Against the H5N6 Strain
Time frame: Day 8, Day 22, Day 43
Seroconversion 1 and 3 weeks post-vaccination 1, and 3 weeks post-vaccination 2, defined as a ≥4-fold increase in HI titer post-vaccination in those with pre-vaccination titer ≥1:10, or a post-vaccination HI titer ≥1:40 for subjects with baseline titer <1:10 Note: The Overall Number of Participants Analyzed (N) represents the total number of participants in the PPS; definitions are provided in the SAP. The Number Analyzed (n) at each timepoint corresponds to the number of participants with an available serum analysis result for the relevant strain at that timepoint. Instances where n<N reflect missing serum samples or non-evaluable results. All participants included in the Overall Number of Participants Analyzed contributed data to the analysis at one or more timepoints.

11 secondary outcomes

GMT of HI Antibodies Against the H5N1 Strain
Time frame: Day 1, Day 8, Day 22, Day 43, Day 202
GMFI of HI Antibodies Against the H5N1 Strain
Time frame: Day 1, Day 8, Day 22, Day 43, Day 202
Percentage of Subjects With HI Titers ≥1:40 Against the H5N1 Strain
Time frame: Day 1, Day 8, Day 22, Day 43, Day 202
Percentage of Subjects With Seroconversion Against the H5N1 Strain
Time frame: Day 8, Day 22, Day 43, Day 202
GMT of HI Antibodies Against the H5N6 Strain
Time frame: Day 202
GMFI of HI Antibodies Against the H5N6 Strain
Time frame: Day 1, Day 202
Percentage of Subjects With HI Titers ≥1:40 Against the H5N6 Strain
Time frame: Day 202
Percentage of Subjects With Seroconversion Against the H5N6 Strain
Time frame: Day 202
Frequency and Severity of Solicited Local and Systemic Adverse Events (AEs)
Time frame: Day 1 through Day 7 and Day 22 through Day 28
Frequency and Severity of Unsolicited AEs
Time frame: Day 1 through Day 43
Frequency of Serious AEs (SAEs), AEs Leading to Withdrawal, AEs of Special Interest (AESI) and Medically Attended AEs (MAAEs)
Time frame: Day 1 through Day 202

Results and safety

Results posted to the registry on 13 May 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
Group 1	81	75
Group 2	78	74
Group 3	101	95

Primary outcome: Geometric Mean Titer (GMT) of Hemagglutination Inhibition (HI) Antibodies Against the H5N6 Strain

Time frame: Day 1, Day 8, Day 22, Day 43. Geometric mean (95% Confidence Interval). Unit: titer

Measure	Group 1 n = 74	Group 2 n = 69	Group 3 n = 95
Day 1	5.48 (5.07 to 5.92)	5.55 (5.13 to 6.01)	5.47 (5.12 to 5.85)
Day 8	20.39 (15.22 to 27.33)	23.67 (17.47 to 32.06)	7.97 (6.21 to 10.23)
Day 22	46.89 (34.62 to 63.50)	66.73 (48.85 to 91.14)	12.14 (9.30 to 15.85)
Day 43	58.16 (43.21 to 78.28)	50.55 (37.21 to 68.68)	30.76 (23.78 to 39.79)

Population analysed: Per-protocol set defined as all subjects who correctly received the study vaccine, provided at least one evaluable serum sample at relevant timepoints, had no major protocol deviations leading to exclusion, and were not excluded due to other reasons prior to unblinding or analysis.

Primary outcome: Geometric Mean Fold Increase (GMFI) of HI Antibodies Against the H5N6 Strain

Time frame: Day 1, Day 8, Day 22, Day 43. Geometric mean (95% Confidence Interval). Unit: ratio

Measure	Group 1 n = 72	Group 2 n = 66	Group 3 n = 92
Day 8 / Day 1	3.71 (2.77 to 4.98)	4.31 (3.18 to 5.84)	1.45 (1.13 to 1.86)
Day 22 / Day 1	8.52 (6.29 to 11.54)	12.13 (8.88 to 16.57)	2.21 (1.69 to 2.88)
Day 43 / Day 1	10.54 (7.83 to 14.19)	9.16 (6.74 to 12.45)	5.58 (4.31 to 7.21)

Primary outcome: Percentage of Subjects With HI Titers ≥1:40 Against the H5N6 Strain

Time frame: Day 1, Day 8, Day 22, Day 43. Number (95% Confidence Interval). Unit: % of participants

Measure	Group 1 n = 74	Group 2 n = 69	Group 3 n = 95
Day 1	0.0 (0.00 to 4.99)	0.0 (0.00 to 5.44)	1.1 (0.03 to 5.91)
Day 8	29.4 (18.98 to 41.71)	39.1 (27.10 to 52.07)	9.9 (4.62 to 17.95)
Day 22	60.8 (48.77 to 71.96)	65.2 (52.79 to 76.29)	20.7 (12.92 to 30.36)
Day 43	73.2 (61.41 to 83.06)	59.1 (46.29 to 71.05)	50.0 (39.39 to 60.61)

Primary outcome: Percentage of Subjects With Seroconversion Against the H5N6 Strain

Time frame: Day 8, Day 22, Day 43. Number (95% Confidence Interval). Unit: % of participants

Measure	Group 1 n = 72	Group 2 n = 66	Group 3 n = 92
Day 8	28.4 (18.01 to 40.69)	36.1 (24.16 to 49.37)	8.9 (3.92 to 16.77)
Day 22	59.7 (47.5 to 71.12)	63.6 (50.87 to 75.13)	18.9 (11.41 to 28.51)
Day 43	71.0 (58.84 to 81.31)	55.6 (42.49 to 68.08)	47.2 (36.51 to 58.06)

11 secondary outcomes are reported in the full results.

Adverse events

Time frame: SAEs, AEs leading to withdrawal from the study, adverse events of special interest (AESIs), and MAAEs Day 1 through Day 202, other AEs Day 1 through Day 43. Other adverse events reported at 5% frequency or more

Group	Serious adverse events	Other adverse events	Deaths
Group 1	3 of 80 (3.8%)	12 of 80 (15%)	1 of 80
Group 2	3 of 78 (3.8%)	5 of 78 (6.4%)	0 of 78
Group 3	4 of 100 (4%)	7 of 100 (7%)	0 of 100

Loading the posted results from ClinicalTrials.gov…

Research links

Official record on ClinicalTrials.govLast updated by the sponsor 13 May 2026.
Posted resultsParticipant flow, baseline, all outcome measures and adverse events.
Individual participant dataSharing planned: Undecided

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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.

Therapeutic Area Head study chair

Seqirus

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

Questions about this trial

What is this clinical trial studying?

A Phase 2 study testing aH5N6c on Day 1 and aH5N6c on Day 22 in people with Influenza, Human and Influenza in Birds, run by Seqirus at 18 sites in United States.

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 2 inclusion and 13 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 13 May 2026. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 18 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 13 May 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?

Geometric Mean Titer (GMT) of Hemagglutination Inhibition (HI) Antibodies Against the H5N6 Strain (time frame: Day 1, Day 8, Day 22, Day 43). The study lists 4 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 NCT05422326.

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 13 May 2026.