Influenza, HumanPhase 1/2NCT06602531

Safety and Immunogenicity Study of Self-Amplifying RNA Pandemic Influenza Vaccine in Adults

A Phase 1/2 study testing ARCT-2304 in people with Influenza, Human, run by Arcturus Therapeutics, Inc. at 4 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

The goal of this clinical trial is to evaluate the safety and immune responses of three different dose levels a self-amplifying RNA pandemic influenza vaccine (ARCT-2304) in adults. Read more about this study

Who is it for?: Ages 18 to 80 yearsHealthy volunteers can take part
Conditions the study is for: Influenza, Human
What is being tested?: ARCT-2304
Type of treatment: Vaccines, Injection or infusion
Could I receive a placebo?: Yes, some participants may receive a placebo
How many people: 212 participants
Where: 4 sitesUnited States
Study dates: 10 Dec 2024to 5 Dec 2025
Phase: Phase 1/2
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 to 80 years
All sexes
Healthy volunteers accepted
Adult, Older adult

Main Inclusion Criteria:

Individuals are male or female adults 18-80 years of age.
Healthy participants or participants with pre-existing stable medical conditions.
Individuals of childbearing potential must be willing to adhere to contraceptive requirements.

Main Exclusion Criteria:

Individuals with acute medical conditions or febrile illness, including body temperature ≥100.4°F (≥38.0°C measured by any method) within 3 days prior to randomization.
Individuals with a known history of severe hypersensitivity reactions, including anaphylaxis, or other significant adverse reactions to any mRNA vaccine, influenza vaccine, or excipients.
Individuals with a history of myocarditis, pericarditis, myopericarditis, or cardiomyopathy.
Individuals who received any influenza vaccine within 3 months prior to first vaccine administration or plan to receive an influenza vaccine during the study period.
Individuals who have received mRNA vaccination within 60 days before the first vaccine administration.
Individuals who have received or plan to receive an A/H5N1 influenza vaccine and/or individuals who had substantial exposure to or direct contact with poultry, wild birds, live cattle, or raw milk.

Trial locations and contacts

4 sites in 1 country.

United States4 sites

CTI Clinical Research Center
Cincinnati, Ohio, 45212
Velocity Clinical Research
La Mesa, California, 91942
Tekton Research
Longmont, Colorado, 80501
Velocity Clinical Research
San Bernardino, California, 92408

Other trials in United States

About this study

Official title: A Phase 1, First-in-human, Randomized, Observer-blind, Parallel Design, Controlled, Dose Level and Schedule-finding Study to Evaluate the Safety, Reactogenicity, and Immunogenicity of a Self-Amplifying mRNA Pandemic Influenza Vaccine (ARCT-2304) When Administered to Healthy Adults

To evaluate safety and reactogenicity of different dose levels of the ARCT-2304 vaccine
To describe the Immune responses of different dose levels of the ARCT-2304 vaccine as measured by hemagglutination inhibition (HAI) and neuraminidase enzyme-linked lectin (ELLA) antibody responses

Researchers will compare the results with licensed influenza vaccines to select the most optimal dose level and schedule for vaccine administration in terms of safety and immunogenicity for further development of the vaccine.

Participants will receive 2 doses of the ARCT-2304 vaccine or 1 dose of licensed influenza vaccine and 1 dose of placebo.

They will be asked:

to complete a daily diary for 7 days after each vaccination, answering questions how they have been feeling on that day.
to provide blood samples at each visit in the clinic
to comply with all study visits and procedures (e.g., be available for planned telephone contacts and unscheduled clinic visits, if required)

Read the detailed description

Phase 1, first-in-human, randomized, controlled, observer blind, dose level and schedule-finding study, to evaluate the safety, reactogenicity, and immunogenicity of a self-amplifying mRNA pandemic influenza (H5N1) vaccine (ARCT-2304) when administered as a 2-dose vaccination series to healthy adults in comparison with an inactivated influenza vaccine.

Study drug (ARCT-2304 or control) will be administered as a 2-dose vaccination series as an intramuscular (IM) injection. The study comprises two parts.

In Part 1, 120 participants (young adults) will be randomized to one of the three dose levels of the ARCT-2304 vaccine or control vaccine. Participants will be further randomized to one of the two different vaccination schedules.

In Part 2, 80 participants (older adults) will be randomized to one of the three dose levels of the ARCT-2304 vaccine or control vaccine. Participants will be further randomized to one of the two different vaccination schedules.

Investigational Vaccine: ARCT-2304

Control Vaccines: licensed influenza vaccines

Conditions: Influenza, Human
Being tested: ARCT-2304, Control vaccine younger adults, Control vaccine older adults, Placebo Vaccine
Keywords: Influenza, Vaccine
Medical subject headings: Influenza, Human

What participants receive

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

ARCT-2304Biological
Also called Self-Amplifying mRNA pandemic Influenza vaccine
Each participant will receive 2-dose regimen intramuscular (IM) dose into the deltoid muscle.
Control vaccine younger adultsBiological
Also called Influenza vaccine
Each participant will receive one intramuscular (IM) dose into the deltoid muscle.
Control vaccine older adultsBiological
Also called Influenza vaccine
Each participant will receive one intramuscular (IM) dose into the deltoid muscle.
Placebo VaccineOther
Also called saline
Each participant will receive one intramuscular (IM) dose into the deltoid muscle.

Study groups in NCT06602531
Study group	Role	What they receive
Low dose of ARCT-2304, Schedule 1, Young Adults	Experimental	Low dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: ARCT-2304 Receives: Biological: ARCT-2304
Mid dose of ARCT-2304, Schedule 1, Young Adults	Experimental	Mid dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: ARCT-2304 Receives: Biological: ARCT-2304
High dose of ARCT-2304, Schedule 1, Young Adults	Experimental	High dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: ARCT-2304 Receives: Biological: ARCT-2304
Control, Schedule 1, Young Adults	Active comparator	Control Vaccine (dose 1) and placebo (dose 2) administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: Comparator vaccine younger adult and saline placebo vaccine Receives: Biological: Control vaccine younger adults; Other: Placebo Vaccine
Low dose of ARCT-2304, Schedule 1, Older Adults	Experimental	Low dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: ARCT-2304 Receives: Biological: ARCT-2304
Mid dose of ARCT-2304, Schedule 1, Older Adults	Experimental	Mid dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: ARCT-2304 Receives: Biological: ARCT-2304
High dose of ARCT-2304, Schedule 1, Older Adults	Experimental	High dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: ARCT-2304 Receives: Biological: ARCT-2304
Control, Schedule 1, Older Adults	Active comparator	Older Adults Control Vaccine (dose 1) and placebo (dose 2) administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: Comparator vaccine older adult and saline Receives: Biological: Control vaccine older adults; Other: Placebo Vaccine
Low dose of ARCT-2304, Schedule 2, Young Adults	Experimental	Low dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: ARCT-2304 Receives: Biological: ARCT-2304
Mid dose of ARCT-2304, Schedule 2, Young Adults	Experimental	Mid dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: ARCT-2304 Receives: Biological: ARCT-2304
High dose of ARCT-2304, Schedule 2, Young Adults	Experimental	High dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: ARCT-2304 Receives: Biological: ARCT-2304
Control, Schedule 2, Young Adults	Active comparator	Young Adults Control Vaccine (dose 1) and placebo (dose 2) administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: Comparator vaccine younger adult and saline placebo vaccine Receives: Biological: Control vaccine younger adults; Other: Placebo Vaccine
Low dose of ARCT-2304, Schedule 2, Older Adults	Experimental	Low dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: ARCT-2304 Receives: Biological: ARCT-2304
Mid dose of ARCT-2304, Schedule 2, Older Adults	Experimental	Mid dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: ARCT-2304 Receives: Biological: ARCT-2304
High dose of ARCT-2304, Schedule 2, Older Adults	Experimental	High dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: ARCT-2304 Receives: Biological: ARCT-2304
Control, Schedule 2, Older Adults	Active comparator	Older Adults Control Vaccine (dose 1) and placebo (dose 2) administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: Comparator vaccine older adult and saline placebo vaccine Receives: Biological: Control vaccine older adults; Other: Placebo Vaccine

What is being measured

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

Number of Participants With Solicited Adverse Events (AEs) Within 7 Days After Each Vaccination
The following solicited local and systemic AEs were recorded from Day 1 to 7 days after each vaccination (dose): Injection site pain, Erythema, Swelling, Fatigue, Headache, Myalgia, Arthralgia, Dizziness, Nausea, Chills, Fever (≥100.4 °Fahrenheit [F] /≥38.0 °Celsius [C]). A summary of all Serious Adverse Events and Other Adverse Events (non-serious) regardless of causality is located in the 'Reported Adverse Events' Section.
Measured: 7 days post each dose
Number of Participants With Unsolicited AEs Within 28 Days After Each Vaccination
An AE was any untoward medical occurrence in a participant or participant administered a medicinal product, whether or not considered related to the trial vaccine. An unsolicited AE was defined as any AE not included in the list of solicited AEs (i.e., any event other than injection site pain, erythema, swelling, fatigue, headache, myalgia, arthralgia, dizziness, nausea, chills, or fever (≥100.4 °F / ≥38.0 °C). Solicited AEs that lasted for more than 7 days were considered as unsolicited AEs. Unsolicited AEs were recorded from Day 1 up to 28 days after each vaccination (dose). A summary of all Serious Adverse Events and Other Adverse Events (non-serious) regardless of causality is located in the 'Reported Adverse Events' Section'.
Measured: D1,29 Cohorts: up to Day 29 and up to Day 57 (28 days post each dose), D1,57 Cohorts: up to Day 29 and up to Day 85 (28 days post each dose)
Number of Participants With Serious Adverse Events (SAEs), Medically Attended AEs (MAAEs), AEs of Special Interest (AESIs), and AEs Leading To Early Termination From Day 1 to 28 Days After Second Vaccination
An SAE was defined as any AE that resulted in death, was life-threatening, resulted in persistent disability/incapacity, or required inpatient hospitalization or prolongation of existing hospitalization. AEs potentially associated with messenger ribonucleic acid (mRNA) vaccines and influenza vaccines were reported as AESIs. MAAEs were defined as AEs with medically attended visits including hospital, emergency room, urgent care clinic, or other visits (including phone/telehealth visits) to or from medical personnel for any reason but did not fulfil seriousness criteria. A summary of all Serious Adverse Events and Other Adverse Events (non-serious) regardless of causality is located in the 'Reported Adverse Events' Section'.
Measured: D1,29 Cohorts: up to Day 57, D1,57 Cohorts: up to Day 85
Geometric Mean Titer of Antibody Response to Hemagglutinin (HA) Glycoprotein Measured By Hemagglutinin Inhibition (HAI) Assay
A serum HAI assay was used for measuring HA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Antibody titers were expressed as Geometric Mean Titers.
Measured: D1,29 Cohorts: Day 1, Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 1, Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
Geometric Mean Titer of Antibody Response to Neuraminidase (NA) Glycoprotein Measured By Enzyme-linked Lectin Assay (ELLA)
A serum ELLA assay was used for measuring NA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Antibody titers were expressed as Geometric Mean Titers.
Measured: D1,29 Cohorts: Day 1, Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 1, Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
Geometric Mean Fold Rise of Antibody Response to HA Glycoprotein Measured By HAI Assay
A serum HAI assay was used for measuring HA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Geometric Mean Fold Rise was reported as a ratio to Day 1.
Measured: D1,29 Cohorts: Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
Geometric Mean Fold Rise of Antibody Response to NA Glycoprotein Measured By ELLA
A serum ELLA assay was used for measuring NA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Geometric Mean Fold Rise was reported as a ratio to Day 1.
Measured: D1,29 Cohorts: Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
Percentage of Participants With Seroconversion of Antibody Response to HA Glycoprotein Measured By HAI Assay
A serum HAI assay was used for measuring HA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Seroconversion was recorded if participant had pre-vaccination antibody titer < Lower Limit Of Quantitation (LLOQ) and a post-vaccination antibody titer ≥ 4 x LLOQ, or a pre-vaccination antibody titer ≥LLOQ and a ≥4-fold increase in post-vaccination antibody titer.
Measured: D1,29 Cohorts: Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
Percentage of Participants With Seroconversion of Antibody Response to NA Glycoprotein Measured By ELLA
A serum ELLA assay was used for measuring NA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Seroconversion was recorded if participant had pre-vaccination antibody titer < LLOQ and a post-vaccination antibody titer ≥ 4 x LLOQ, or a pre-vaccination antibody titer ≥LLOQ and a ≥4-fold increase in post-vaccination antibody titer.
Measured: D1,29 Cohorts: Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
Percentage of Participants With HAI Titers Above or Equal to Prespecified Thresholds
A serum HAI assay was used for measuring HA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. The prespecified antibody threshold levels were as follows: ≥1:10, ≥1:20, ≥1:40, ≥1:80, ≥1:160, and ≥1:320.
Measured: D1,29 Cohorts: Day 57 (28 days post dose 2), D1,57 Cohorts: Day 85 (28 days post dose 2)
Percentage of Participants With ELLA Titers Above or Equal to Prespecified Thresholds
A serum ELLA assay was used for measuring NA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. The prespecified antibody threshold levels were as follows: ≥1:10, ≥1:20, ≥1:40, ≥1:80, ≥1:160, and ≥1:320.
Measured: D1,29 Cohorts: Day 57 (28 days post dose 2), D1,57 Cohorts: Day 85 (28 days post dose 2)

Secondary outcomes (13)

Number of Participants With SAEs, MAAEs, AESIs, and AEs Leading To Early Termination From Day 1 to Day 240
A SAE was defined as any AE that resulted in death, was life-threatening, resulted in persistent disability/incapacity, or required inpatient hospitalization or prolongation of existing hospitalization. AEs potentially associated with mRNA vaccines and influenza vaccines were reported as AESIs. MAAEs were defined as AEs with medically attended visits including hospital, emergency room, urgent care clinic, or other visits (including phone/telehealth visits) to or from medical personnel for any reason, but did not fulfil seriousness criteria. A summary of all Serious Adverse Events and Other Adverse Events (non-serious) regardless of causality is located in the 'Reported Adverse Events' Section.
Measured: Day 1 to Day 240
Geometric Mean Titer of Antibody Response To HA Glycoprotein Measured By HAI Assay at Day 240
A serum HAI assay was used for measuring HA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Antibody titers were expressed as Geometric Mean Titers.
Measured: Day 240
Geometric Mean Titer of Antibody Response to NA Glycoprotein Measured By ELLA at Day 240
A serum ELLA assay was used for measuring NA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Antibody titers were expressed as Geometric Mean Titers.
Measured: Day 240
Geometric Mean Fold Rise of Antibody Response to HA Glycoprotein Measured By HAI Assay at Day 240
A serum HAI assay was used for measuring HA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Geometric Mean Fold Rise was reported as a ratio to Day 1.
Measured: Day 240
Geometric Mean Fold Rise of Antibody Response to NA Glycoprotein Measured By ELLA at Day 240
A serum ELLA assay was used for measuring NA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Geometric Mean Fold Rise was reported as a ratio to Day 1.
Measured: Day 240
Percentage of Participants With Seroconversion of Antibody Response to HA Glycoprotein Measured By HAI Assay At Day 240
A serum HAI assay was used for measuring HA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Seroconversion was recorded if participant had pre-vaccination antibody titer < LLOQ and a post-vaccination antibody titer ≥ 4 x LLOQ, or a pre-vaccination antibody titer ≥LLOQ and a ≥4-fold increase in post-vaccination antibody titer.
Measured: Day 240
Percentage of Participants With Seroconversion of Antibody Response to NA Glycoprotein Measured By ELLA At Day 240
A serum ELLA assay was used for measuring NA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Seroconversion was recorded if participant had pre-vaccination antibody titer < LLOQ and a post-vaccination antibody titer ≥ 4 x LLOQ, or a pre-vaccination antibody titer ≥LLOQ and a ≥4-fold increase in post-vaccination antibody titer.
Measured: Day 240
Percentage of Participants With HAI Titers Above Or Equal To Prespecified Thresholds At Day 240
A serum HAI assay was used for measuring HA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. The prespecified antibody threshold levels were as follows: ≥1:10, ≥1:20, ≥1:40, ≥1:80, ≥1:160, and ≥1:320.
Measured: Day 240
Percentage of Participants With ELLA Titers Above Or Equal to Prespecified Thresholds At Day 240
A serum ELLA assay was used for measuring NA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. The prespecified antibody threshold levels were as follows: ≥1:10, ≥1:20, ≥1:40, ≥1:80, ≥1:160, and ≥1:320.
Measured: Day 240
Geometric Mean Titer of Antibody Response Against HA Glycoprotein Measured By Microneutralization (MN) Assay
Neutralizing antibody response to H5 hemagglutinin was measured by MN assay. Antibody titers were expressed as Geometric Mean Titers.
Measured: D1,29 Cohorts: Day 1, Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 1, Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
Geometric Mean Fold Rise of Antibody Response to HA Glycoprotein Measured By MN Assay
Neutralizing antibody response to H5 hemagglutinin was measured by MN assay. Geometric Mean Fold Rise was reported as a ratio to Day 1.
Measured: D1,29 Cohorts: Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
Percentage of Participants With Seroconversion of Antibody Response to HA Glycoprotein Measured By MN Assay
Neutralizing antibody response to H5 hemagglutinin was measured by MN assay. Seroconversion was recorded if participant had pre-vaccination antibody titer < LLOQ and a post-vaccination antibody titer ≥ 4 x LLOQ, or a pre-vaccination antibody titer ≥LLOQ and a ≥4-fold increase in post-vaccination antibody titer.
Measured: D1,29 Cohorts: Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
Percentage of Participants With MN Titers Above Or Equal To Prespecified Thresholds
Neutralizing antibody response to H5 hemagglutinin was measured by MN assay. The prespecified antibody threshold levels were as follows: ≥1:10, ≥1:20, ≥1:40, ≥1:80, ≥1:160, and ≥1:320.
Measured: D1,29 Cohorts: Day 57 (28 days post dose 2), D1,57 Cohorts: Day 85 (28 days post dose 2)

Timeline

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

10 Dec 20245 Dec 2025

First posted19 Sep 2024
Study start10 Dec 2024
Primary completion13 Jun 2025
Study completion5 Dec 2025

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 1/2
Primary purpose: Prevention
Allocation: Randomised
Intervention model: Parallel groups
Masking: Quadruple blind
Who is masked: Participant, Care provider, Investigator, Outcomes assessor
Enrolment: 212 participants (actual)

IDs, dates and publications

ClinicalTrials.gov ID: NCT06602531
Sponsor's protocol ID: ARCT-2304-01
Status last verified: Aug 2026
First submitted: 16 Sep 2024
Last updated: 4 Sep 2026
Results posted: Yes, on ClinicalTrials.gov
Data monitoring committee: Yes
FDA-regulated drug: Yes
FDA-regulated device: No
Individual data sharing: No: Individual participant data will only be made available to study investigators at this time.

Publications

Pragalos AA, Pacciarini F, Jin H, Hopkins T, Zhang Y, Bugarini R, Liu X, Sullivan BM, Verhoeven C, Smolenov I. Extended dosing intervals enhance the durability of a self-amplifying mRNA vaccine against pandemic H5N1 influenza: a randomized, observer-blind, dose-finding Phase I study. Nat Commun. 2026 Sep 24;17(1):11091. doi: 10.1038/s41467-026-78031-9.
PubMed 42928290

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 4 Sep 2026. Recruitment status is as the sponsor reported it: confirm with the study team.

Official title: A Phase 1, First-in-human, Randomized, Observer-blind, Parallel Design, Controlled, Dose Level and Schedule-finding Study to Evaluate the Safety, Reactogenicity, and Immunogenicity of a Self-Amplifying mRNA Pandemic Influenza Vaccine (ARCT-2304) When Administered to Healthy Adults
ClinicalTrials.gov ID: NCT06602531
Acronym / sponsor ID: ARCT-2304-01
Conditions: Influenza, Human
Keywords: Influenza, Vaccine
Phase: Phase 1/2
Study type: Interventional
Recruitment status: Completed
Enrolment: 212 participants (actual)
Lead sponsor: Arcturus Therapeutics, Inc.Industry (pharma, biotech, devices)
Collaborators: Biomedical Advanced Research and Development Authority
Study start: 10 Dec 2024 (actual)
Primary completion: 13 Jun 2025 (actual)
Study completion: 5 Dec 2025 (actual)
First posted: 19 Sep 2024 (actual)
Results: Posted 4 Sep 2026

Clinical summary

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

To evaluate safety and reactogenicity of different dose levels of the ARCT-2304 vaccine
To describe the Immune responses of different dose levels of the ARCT-2304 vaccine as measured by hemagglutination inhibition (HAI) and neuraminidase enzyme-linked lectin (ELLA) antibody responses

Participants will receive 2 doses of the ARCT-2304 vaccine or 1 dose of licensed influenza vaccine and 1 dose of placebo.

They will be asked:

to complete a daily diary for 7 days after each vaccination, answering questions how they have been feeling on that day.
to provide blood samples at each visit in the clinic
to comply with all study visits and procedures (e.g., be available for planned telephone contacts and unscheduled clinic visits, if required)

Detailed description

Study drug (ARCT-2304 or control) will be administered as a 2-dose vaccination series as an intramuscular (IM) injection. The study comprises two parts.

Investigational Vaccine: ARCT-2304

Control Vaccines: licensed influenza vaccines

Study design

Primary purpose: Prevention
Allocation: Randomised
Intervention model: Parallel groups
Masking: Quadruple blind (participant, care provider, investigator, outcomes assessor)
Number of arms: 16

Arm	Type	Receives
Low dose of ARCT-2304, Schedule 1, Young Adults	Experimental	Biological: ARCT-2304Low dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: ARCT-2304
Mid dose of ARCT-2304, Schedule 1, Young Adults	Experimental	Biological: ARCT-2304Mid dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: ARCT-2304
High dose of ARCT-2304, Schedule 1, Young Adults	Experimental	Biological: ARCT-2304High dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: ARCT-2304
Control, Schedule 1, Young Adults	Active comparator	Biological: Control vaccine younger adults, Other: Placebo VaccineControl Vaccine (dose 1) and placebo (dose 2) administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: Comparator vaccine younger adult and saline placebo vaccine
Low dose of ARCT-2304, Schedule 1, Older Adults	Experimental	Biological: ARCT-2304Low dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: ARCT-2304
Mid dose of ARCT-2304, Schedule 1, Older Adults	Experimental	Biological: ARCT-2304Mid dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: ARCT-2304
High dose of ARCT-2304, Schedule 1, Older Adults	Experimental	Biological: ARCT-2304High dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: ARCT-2304
Control, Schedule 1, Older Adults	Active comparator	Biological: Control vaccine older adults, Other: Placebo VaccineOlder Adults Control Vaccine (dose 1) and placebo (dose 2) administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 1 Investigational Vaccine: Comparator vaccine older adult and saline
Low dose of ARCT-2304, Schedule 2, Young Adults	Experimental	Biological: ARCT-2304Low dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: ARCT-2304
Mid dose of ARCT-2304, Schedule 2, Young Adults	Experimental	Biological: ARCT-2304Mid dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: ARCT-2304
High dose of ARCT-2304, Schedule 2, Young Adults	Experimental	Biological: ARCT-2304High dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: ARCT-2304
Control, Schedule 2, Young Adults	Active comparator	Biological: Control vaccine younger adults, Other: Placebo VaccineYoung Adults Control Vaccine (dose 1) and placebo (dose 2) administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: Comparator vaccine younger adult and saline placebo vaccine
Low dose of ARCT-2304, Schedule 2, Older Adults	Experimental	Biological: ARCT-2304Low dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: ARCT-2304
Mid dose of ARCT-2304, Schedule 2, Older Adults	Experimental	Biological: ARCT-2304Mid dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: ARCT-2304
High dose of ARCT-2304, Schedule 2, Older Adults	Experimental	Biological: ARCT-2304High dose of ARCT-2304 administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: ARCT-2304
Control, Schedule 2, Older Adults	Active comparator	Biological: Control vaccine older adults, Other: Placebo VaccineOlder Adults Control Vaccine (dose 1) and placebo (dose 2) administered through intramuscular injection in the deltoid muscle. Interventions: 2-dose regimen, schedule 2 Investigational Vaccine: Comparator vaccine older adult and saline placebo vaccine

Who may qualify

Ages: 18 to 80 years
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

Intervention	Type	Arms
ARCT-2304Also: Self-Amplifying mRNA pandemic Influenza vaccineEach participant will receive 2-dose regimen intramuscular (IM) dose into the deltoid muscle.	Biological	High dose of ARCT-2304, Schedule 1, Older Adults, High dose of ARCT-2304, Schedule 1, Young Adults, High dose of ARCT-2304, Schedule 2, Older Adults, High dose of ARCT-2304, Schedule 2, Young Adults, Low dose of ARCT-2304, Schedule 1, Older Adults, Low dose of ARCT-2304, Schedule 1, Young Adults, Low dose of ARCT-2304, Schedule 2, Older Adults, Low dose of ARCT-2304, Schedule 2, Young Adults, Mid dose of ARCT-2304, Schedule 1, Older Adults, Mid dose of ARCT-2304, Schedule 1, Young Adults, Mid dose of ARCT-2304, Schedule 2, Older Adults, Mid dose of ARCT-2304, Schedule 2, Young Adults
Control vaccine younger adultsAlso: Influenza vaccineEach participant will receive one intramuscular (IM) dose into the deltoid muscle.	Biological	Control, Schedule 1, Young Adults, Control, Schedule 2, Young Adults
Control vaccine older adultsAlso: Influenza vaccineEach participant will receive one intramuscular (IM) dose into the deltoid muscle.	Biological	Control, Schedule 1, Older Adults, Control, Schedule 2, Older Adults
Placebo VaccineAlso: salineEach participant will receive one intramuscular (IM) dose into the deltoid muscle.	Other	Control, Schedule 1, Older Adults, Control, Schedule 1, Young Adults, Control, Schedule 2, Older Adults, Control, Schedule 2, Young Adults

Primary outcome

Number of Participants With Solicited Adverse Events (AEs) Within 7 Days After Each Vaccination
Time frame: 7 days post each dose
The following solicited local and systemic AEs were recorded from Day 1 to 7 days after each vaccination (dose): Injection site pain, Erythema, Swelling, Fatigue, Headache, Myalgia, Arthralgia, Dizziness, Nausea, Chills, Fever (≥100.4 °Fahrenheit [F] /≥38.0 °Celsius [C]). A summary of all Serious Adverse Events and Other Adverse Events (non-serious) regardless of causality is located in the 'Reported Adverse Events' Section.
Number of Participants With Unsolicited AEs Within 28 Days After Each Vaccination
Time frame: D1,29 Cohorts: up to Day 29 and up to Day 57 (28 days post each dose), D1,57 Cohorts: up to Day 29 and up to Day 85 (28 days post each dose)
An AE was any untoward medical occurrence in a participant or participant administered a medicinal product, whether or not considered related to the trial vaccine. An unsolicited AE was defined as any AE not included in the list of solicited AEs (i.e., any event other than injection site pain, erythema, swelling, fatigue, headache, myalgia, arthralgia, dizziness, nausea, chills, or fever (≥100.4 °F / ≥38.0 °C). Solicited AEs that lasted for more than 7 days were considered as unsolicited AEs. Unsolicited AEs were recorded from Day 1 up to 28 days after each vaccination (dose). A summary of all Serious Adverse Events and Other Adverse Events (non-serious) regardless of causality is located in the 'Reported Adverse Events' Section'.
Number of Participants With Serious Adverse Events (SAEs), Medically Attended AEs (MAAEs), AEs of Special Interest (AESIs), and AEs Leading To Early Termination From Day 1 to 28 Days After Second Vaccination
Time frame: D1,29 Cohorts: up to Day 57, D1,57 Cohorts: up to Day 85
An SAE was defined as any AE that resulted in death, was life-threatening, resulted in persistent disability/incapacity, or required inpatient hospitalization or prolongation of existing hospitalization. AEs potentially associated with messenger ribonucleic acid (mRNA) vaccines and influenza vaccines were reported as AESIs. MAAEs were defined as AEs with medically attended visits including hospital, emergency room, urgent care clinic, or other visits (including phone/telehealth visits) to or from medical personnel for any reason but did not fulfil seriousness criteria. A summary of all Serious Adverse Events and Other Adverse Events (non-serious) regardless of causality is located in the 'Reported Adverse Events' Section'.
Geometric Mean Titer of Antibody Response to Hemagglutinin (HA) Glycoprotein Measured By Hemagglutinin Inhibition (HAI) Assay
Time frame: D1,29 Cohorts: Day 1, Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 1, Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
A serum HAI assay was used for measuring HA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Antibody titers were expressed as Geometric Mean Titers.
Geometric Mean Titer of Antibody Response to Neuraminidase (NA) Glycoprotein Measured By Enzyme-linked Lectin Assay (ELLA)
Time frame: D1,29 Cohorts: Day 1, Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 1, Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
A serum ELLA assay was used for measuring NA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Antibody titers were expressed as Geometric Mean Titers.
Geometric Mean Fold Rise of Antibody Response to HA Glycoprotein Measured By HAI Assay
Time frame: D1,29 Cohorts: Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
A serum HAI assay was used for measuring HA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Geometric Mean Fold Rise was reported as a ratio to Day 1.
Geometric Mean Fold Rise of Antibody Response to NA Glycoprotein Measured By ELLA
Time frame: D1,29 Cohorts: Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
A serum ELLA assay was used for measuring NA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Geometric Mean Fold Rise was reported as a ratio to Day 1.
Percentage of Participants With Seroconversion of Antibody Response to HA Glycoprotein Measured By HAI Assay
Time frame: D1,29 Cohorts: Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
A serum HAI assay was used for measuring HA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Seroconversion was recorded if participant had pre-vaccination antibody titer < Lower Limit Of Quantitation (LLOQ) and a post-vaccination antibody titer ≥ 4 x LLOQ, or a pre-vaccination antibody titer ≥LLOQ and a ≥4-fold increase in post-vaccination antibody titer.
Percentage of Participants With Seroconversion of Antibody Response to NA Glycoprotein Measured By ELLA
Time frame: D1,29 Cohorts: Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
A serum ELLA assay was used for measuring NA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. Seroconversion was recorded if participant had pre-vaccination antibody titer < LLOQ and a post-vaccination antibody titer ≥ 4 x LLOQ, or a pre-vaccination antibody titer ≥LLOQ and a ≥4-fold increase in post-vaccination antibody titer.
Percentage of Participants With HAI Titers Above or Equal to Prespecified Thresholds
Time frame: D1,29 Cohorts: Day 57 (28 days post dose 2), D1,57 Cohorts: Day 85 (28 days post dose 2)
A serum HAI assay was used for measuring HA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. The prespecified antibody threshold levels were as follows: ≥1:10, ≥1:20, ≥1:40, ≥1:80, ≥1:160, and ≥1:320.
Percentage of Participants With ELLA Titers Above or Equal to Prespecified Thresholds
Time frame: D1,29 Cohorts: Day 57 (28 days post dose 2), D1,57 Cohorts: Day 85 (28 days post dose 2)
A serum ELLA assay was used for measuring NA-specific antibodies against the A/H5N1/Indonesia/5/2005 influenza strain. The prespecified antibody threshold levels were as follows: ≥1:10, ≥1:20, ≥1:40, ≥1:80, ≥1:160, and ≥1:320.

13 secondary outcomes

Number of Participants With SAEs, MAAEs, AESIs, and AEs Leading To Early Termination From Day 1 to Day 240
Time frame: Day 1 to Day 240
Geometric Mean Titer of Antibody Response To HA Glycoprotein Measured By HAI Assay at Day 240
Time frame: Day 240
Geometric Mean Titer of Antibody Response to NA Glycoprotein Measured By ELLA at Day 240
Time frame: Day 240
Geometric Mean Fold Rise of Antibody Response to HA Glycoprotein Measured By HAI Assay at Day 240
Time frame: Day 240
Geometric Mean Fold Rise of Antibody Response to NA Glycoprotein Measured By ELLA at Day 240
Time frame: Day 240
Percentage of Participants With Seroconversion of Antibody Response to HA Glycoprotein Measured By HAI Assay At Day 240
Time frame: Day 240
Percentage of Participants With Seroconversion of Antibody Response to NA Glycoprotein Measured By ELLA At Day 240
Time frame: Day 240
Percentage of Participants With HAI Titers Above Or Equal To Prespecified Thresholds At Day 240
Time frame: Day 240
Percentage of Participants With ELLA Titers Above Or Equal to Prespecified Thresholds At Day 240
Time frame: Day 240
Geometric Mean Titer of Antibody Response Against HA Glycoprotein Measured By Microneutralization (MN) Assay
Time frame: D1,29 Cohorts: Day 1, Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 1, Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
Geometric Mean Fold Rise of Antibody Response to HA Glycoprotein Measured By MN Assay
Time frame: D1,29 Cohorts: Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
Percentage of Participants With Seroconversion of Antibody Response to HA Glycoprotein Measured By MN Assay
Time frame: D1,29 Cohorts: Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2)
Percentage of Participants With MN Titers Above Or Equal To Prespecified Thresholds
Time frame: D1,29 Cohorts: Day 57 (28 days post dose 2), D1,57 Cohorts: Day 85 (28 days post dose 2)

Results and safety

Results posted to the registry on 4 Sep 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
D1,29 Cohort: ARCT-2304 1.5 µg	26	26
D1,29 Cohort: ARCT-2304 5 µg	26	25
D1,29 Cohort: ARCT-2304 12 µg	27	26
D1,29 Cohort: Control/Placebo	27	24
D1,57 Cohort: ARCT-2304 1.5µg	27	23
D1,57 Cohort: ARCT-2304 5 µg	27	26
D1,57 Cohort: ARCT-2304 12 µg	26	25
D1,57 Cohort: Control/Placebo	26	22

Primary outcome: Number of Participants With Solicited Adverse Events (AEs) Within 7 Days After Each Vaccination

Time frame: 7 days post each dose. Count of participants. Unit: Participants

Measure	D1,29 Cohort: ARCT-2304 1.5 µg n = 26	D1,29 Cohort: ARCT-2304 5 µg n = 26	D1,29 Cohort: ARCT-2304 12 µg n = 27	D1,29 Cohort: Control/Placebo n = 27	D1,57 Cohort: ARCT-2304 1.5µg n = 27	D1,57 Cohort: ARCT-2304 5 µg n = 27	D1,57 Cohort: ARCT-2304 12 µg n = 26	D1,57 Cohort: Control/Placebo n = 26
Post dose 1	17	22	23	19	17	23	23	19
Post dose 2	15	22	24	11	14	21	20	12

Population analysed: SAF included all participants who received at least one dose of trial vaccine and had any evaluable post-vaccination reactogenicity and/or safety data.

Primary outcome: Number of Participants With Unsolicited AEs Within 28 Days After Each Vaccination

Time frame: D1,29 Cohorts: up to Day 29 and up to Day 57 (28 days post each dose), D1,57 Cohorts: up to Day 29 and up to Day 85 (28 days post each dose). Count of participants. Unit: Participants

Measure	D1,29 Cohort: ARCT-2304 1.5 µg n = 26	D1,29 Cohort: ARCT-2304 5 µg n = 26	D1,29 Cohort: ARCT-2304 12 µg n = 27	D1,29 Cohort: Control/Placebo n = 27	D1,57 Cohort: ARCT-2304 1.5µg n = 27	D1,57 Cohort: ARCT-2304 5 µg n = 27	D1,57 Cohort: ARCT-2304 12 µg n = 26	D1,57 Cohort: Control/Placebo n = 26
Post dose 1	7	7	5	5	5	6	4	5
Post dose 2	6	5	7	3	1	2	7	2

Population analysed: SAF included all participants who received at least one dose of trial vaccine and had any evaluable post-vaccination reactogenicity and/or safety data.

Primary outcome: Number of Participants With Serious Adverse Events (SAEs), Medically Attended AEs (MAAEs), AEs of Special Interest (AESIs), and AEs Leading To Early Termination From Day 1 to 28 Days After Second Vaccination

Time frame: D1,29 Cohorts: up to Day 57, D1,57 Cohorts: up to Day 85. Count of participants. Unit: Participants

Measure	D1,29 Cohort: ARCT-2304 1.5 µg n = 26	D1,29 Cohort: ARCT-2304 5 µg n = 26	D1,29 Cohort: ARCT-2304 12 µg n = 27	D1,57 Cohort: ARCT-2304 1.5µg n = 27	D1,57 Cohort: ARCT-2304 5 µg n = 27	D1,57 Cohort: ARCT-2304 12 µg n = 26	D1,57 Cohort: Control/Placebo n = 26
AE leading to early termination	0	0	0	0	1	0	0
MAAE	4	1	5	4	6	3	4
AESI	0	0	0	0	0	1	0
SAE	0	0	0	0	0	2	1

Population analysed: SAF included all participants who received at least one dose of trial vaccine and had any evaluable post-vaccination reactogenicity and/or safety data.

Primary outcome: Geometric Mean Titer of Antibody Response to Hemagglutinin (HA) Glycoprotein Measured By Hemagglutinin Inhibition (HAI) Assay

Time frame: D1,29 Cohorts: Day 1, Day 29 (28 days post dose 1), Day 36 (7 days post dose 2), and Day 57 (28 days post dose 2), D1,57 Cohorts: Day 1, Day 57 (56 days post dose 1), Day 64 (7 days post dose 2), and Day 85 (28 days post dose 2). Geometric mean (95% Confidence Interval). Unit: Titer

Measure	D1,29 Cohort: ARCT-2304 1.5 µg n = 24	D1,29 Cohort: ARCT-2304 5 µg n = 22	D1,29 Cohort: ARCT-2304 12 µg n = 24	D1,57 Cohort: ARCT-2304 1.5µg n = 20	D1,57 Cohort: ARCT-2304 5 µg n = 22	D1,57 Cohort: ARCT-2304 12 µg n = 18
Day 1	5.0 (5.0 to 5.0)	5.0 (5.0 to 5.0)	5.4 (4.6 to 6.3)	5.5 (4.5 to 6.9)	5.0 (5.0 to 5.0)	5.6 (4.4 to 7.2)
28 days post dose 1	5.5 (4.8 to 6.3)	7.5 (5.3 to 10.7)	8.9 (6.1 to 12.9)	–	–	–
56 days post dose 1	–	–	–	7.4 (5.2 to 10.6)	7.4 (5.5 to 9.9)	10.0 (6.8 to 14.8)
7 days post dose 2	13.5 (8.9 to 20.4)	25.7 (16.5 to 40.1)	35.5 (27.6 to 45.5)	26.4 (17.6 to 39.5)	33.1 (24.9 to 44.0)	63.5 (50.1 to 80.4)
28 days post dose 2	17.8 (12.0 to 26.4)	35.3 (23.7 to 52.5)	41.7 (32.3 to 53.9)	37.3 (23.7 to 58.9)	54.8 (42.7 to 70.4)	77.0 (63.4 to 93.6)

Population analysed: Per Protocol Set (PPS) included all participants who received 1 dose of trial vaccine, provided at least 1 post-baseline immunogenicity assessment, correctly received the assigned dose of trial vaccine and had no protocol deviations impacting immunogenicity data. As prespecified, this analysis was not conducted for the control/placebo group. Overall number of participants analyzed = participants evaluable for the outcome measure. Number analyzed = participants evaluable at each timepoint.

13 secondary outcomes are reported in the full results.

Adverse events

Time frame: Day 1 to Day 240. Other adverse events reported at 5% frequency or more

Group	Serious adverse events	Other adverse events	Deaths
D1,29 Cohort: ARCT-2304 1.5 µg	0 of 26 (0%)	7 of 26 (26.9%)	0 of 26
D1,29 Cohort: ARCT-2304 5 µg	0 of 26 (0%)	4 of 26 (15.4%)	0 of 26
D1,29 Cohort: ARCT-2304 12 µg	0 of 27 (0%)	4 of 27 (14.8%)	0 of 27
D1,29 Cohort: Control/Placebo	0 of 27 (0%)	4 of 27 (14.8%)	0 of 27
D1,57 Cohort: ARCT-2304 1.5µg	1 of 27 (3.7%)	2 of 27 (7.4%)	0 of 27
D1,57 Cohort: ARCT-2304 5 µg	0 of 27 (0%)	0 of 27 (0%)	0 of 27
D1,57 Cohort: ARCT-2304 12 µg	2 of 26 (7.7%)	6 of 26 (23.1%)	0 of 26
D1,57 Cohort: Control/Placebo	1 of 26 (3.8%)	0 of 26 (0%)	0 of 26

Loading the posted results from ClinicalTrials.gov…

Research links

Official record on ClinicalTrials.govLast updated by the sponsor 4 Sep 2026.
Posted resultsParticipant flow, baseline, all outcome measures and adverse events.
Derived from this study: PubMed 42928290Pragalos AA, Pacciarini F, Jin H, Hopkins T, Zhang Y, Bugarini R, Liu X, Sullivan BM, Verhoeven C, Smolenov I. Extended dosing intervals enhance the durability of a self-amplifying mRNA vaccine against pandemic H5N1 influenza: a randomized, observer-blind, dose-finding Phase I study. Nat Commun. 2026 Sep 24;17(1):11091. doi: 10.1038/s41467-026-78031-9.
Individual participant dataSharing planned: No. Individual participant data will only be made available to study investigators at this time.

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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

Arcturus Therapeutics

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

Questions about this trial

What is this clinical trial studying?

A Phase 1/2 study testing ARCT-2304 in people with Influenza, Human, run by Arcturus Therapeutics, Inc. at 4 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?

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 4 Sep 2026. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 4 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 combined phase mean?

Phase 1 studies test a treatment in a small group of people for the first time or in a new way, mainly to check safety and find the right dose.

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 4 Sep 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?

Number of Participants With Solicited Adverse Events (AEs) Within 7 Days After Each Vaccination (time frame: 7 days post each dose). The study lists 11 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 NCT06602531, 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 4 Sep 2026.