A Phase 3 interventional study of ARCT-2303 and Influenza vaccine in COVID-19, sponsored by Arcturus Therapeutics, Inc.. Completed at 29 sites in 4 countries. Open to participants aged 18 Years and older, including healthy volunteers. Per ClinicalTrials.gov, last updated 2025-12-12.
Sponsored by Arcturus Therapeutics, Inc. · Phase 3, Interventional, and Prevention
This is a multicenter, observer-blind, randomized, controlled phase 3 study to evaluate the immunogenicity, reactogenicity, and safety of an investigational self-amplifying RNA COVID-19 vaccine (ARCT-2303) administered concomitantly with quadrivalent influenza vaccines or standalone in adults who previously received authorized COVID-19 vaccine.
Approximately 1680 participants previously vaccinated with authorized COVID-19 vaccine will be enrolled in this study in two age cohorts (younger adults and older adults). Within each cohort, participants will be randomly assigned in a ratio of 1:1:1 to receive the ARCT-2303 vaccine concomitantly with a quadrivalent influenza vaccine, the ARCT-2303 vaccine and placebo, or the quadrivalent influenza vaccine and placebo. The assessment of immunogenicity will be performed 28 days after vaccination. To provide equal benefit from the participation in the study and complete seasonal vaccination against COVID-19 and influenza, a switchover vaccine dose (influenza, ARCT-2303 or placebo) will be administered 28 days after initial vaccination. All participants will be followed up for safety assessment until the end of the study.
A historical control group vaccinated on a similar schedule (ARCT-154 vaccine) from a previous study (ARCT-154-J01) will be used to compare with the immunogenicity of the ARCT-2303 vaccine.
Cohort A (younger adults; approximately 1200 participants):
Cohort B (older adults; approximately 480 participants):
7,990 studies on the registry are indexed under COVID-19; 466 are open to participants now.
This study's enrollment of 1,514 is above the median of 102 across 4,364 interventional studies indexed under COVID-19.
Browse COVID-19 studies →Arcturus Therapeutics, Inc. is the lead sponsor of 13 studies on the registry; 2 are open to participants now.
Of its 8 completed or terminated interventional studies of FDA-regulated products, 5 (63%) have results posted.
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.
1, Individuals are male, female, or transgender adults ≥18 years of age.
2. Healthy participants or participants with pre-existing stable medical conditions.
3. Participant or legally authorized representatives must freely provide documented prior to study procedures being performed.
4. Individuals must have been previously vaccinated with COVID-19 vaccines.
5. Individuals of must be willing to adhere to requirements.
Exclusion Criteria:
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.
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 weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
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.
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
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.
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.
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.
Immunosuppression
A weakened immune system. It can come from an illness, such as HIV or some blood cancers, or from medicines that turn the immune system down, for example after an organ transplant or for an autoimmune disease; steroids at higher doses count.
Read whether the line is about a condition or about medicines, and which medicines and doses it means.
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.
HIV
The human immunodeficiency virus, which weakens the immune system.
Many studies now accept people whose HIV is controlled on treatment, judged by the viral load and the CD4 count. Check the limits this study sets.
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.
Participants will receive one 0.5-mL IM (intramuscular) dose of ARCT-2303 and one 0.5-mL IM dose of influenza vaccine on Day 1 followed by a 0.5-mL IM dose of placebo on Day 29.
Biological: ARCT-2303 · Biological: Influenza vaccine · Other: Placebo
Participants will receive one 0.5-mL IM dose of ARCT-2303 and one 0.5-mL IM dose of placebo on Day 1 followed by a 0.5-mL IM dose of influenza vaccine on Day 29.
Biological: ARCT-2303 · Biological: Influenza vaccine · Other: Placebo
Participants will receive one 0.5-mL IM dose of influenza vaccine and one 0.5-mL IM dose of placebo on Day 1 followed by a 0.5-mL IM dose of ARCT-2303 on Day 29.
Biological: ARCT-2303 · Biological: Influenza vaccine · Other: Placebo
Participants will receive one 0.5-mL IM dose of ARCT-2303 and one 0.5-mL IM dose of influenza vaccine on Day 1 followed by a 0.5-mL IM dose of placebo on Day 29.
Biological: ARCT-2303 · Biological: Influenza vaccine, adjuvanted · Other: Placebo
Participants will receive one 0.5-mL IM dose of ARCT-2303 and one 0.5-mL IM dose of placebo on Day 1 followed by a 0.5-mL IM dose of influenza vaccine on Day 29.
Biological: ARCT-2303 · Biological: Influenza vaccine, adjuvanted · Other: Placebo
Participants will receive one 0.5-mL IM dose of influenza vaccine and one 0.5-mL IM dose of placebo on Day 1 followed by a 0.5-mL IM dose of ARCT-2303 on Day 29.
Biological: ARCT-2303 · Biological: Influenza vaccine, adjuvanted · Other: Placebo
Self-Amplifying RNA COVID-19 vaccine (Omicron XBB.1.5)
Licensed cell-based influenza vaccine
Licensed influenza vaccine, adjuvanted
0.9% saline
Groups 2a and 2b and ARCT-154-J01 Historical Control: Geometric Mean Titers (GMT) of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Neutralizing Antibody Titers Against Omicron XBB.1.5 Subvariant at Day 29
Time frame: Day 29
Groups 2a and 2b and ARCT-154-J01 Historical Control: Number of Participants With Seroconversion to SARS-CoV-2 Neutralizing Antibody Against Omicron XBB.1.5 Subvariant at Day 29
Seroconversion was defined as either a pre-vaccination titer below the lower limit of quantitation (LLOQ) and a postvaccination titer ≥4xLLOQ; or a pre-vaccination titer ≥LLOQ and a ≥4-fold increase in post-vaccination titer.
Time frame: Day 29
Groups 1a and 3a: Adjusted Hemagglutination Inhibition (HI) GMTs Against Influenza Vaccine Strains at Day 29
Influenza vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata.
Time frame: Day 29
Groups 1a and 2a: Adjusted GMTs of SARS-CoV-2 Neutralizing Antibody Against Omicron XBB.1.5 Subvariant at Day 29
Time frame: Day 29
Groups 1a and 2a: GMT of SARS-CoV-2 Neutralizing Antibodies Against Omicron XBB.1.5 Subvariant at Days 1, 29 and 181
Time frame: Group 1a: Days 1 and 29; Group 2a: Days 1, 29, and 181
Groups 1a and 2a: Geometric Mean Fold Rise (GMFR) of SARS-CoV-2 Neutralizing Antibodies Against Omicron XBB.1.5 Subvariant at Days 29 and 181
GMFR is reported as a ratio to Day 1.
Time frame: Group 1a: Day 29; Group 2a: Days 29 and 181
Groups 1a and 2a: Number of Participants With Seroconversion of SARS-CoV-2 Neutralizing Antibodies Against Omicron XBB.1.5 Subvariant at Day 29
Seroconversion was defined as either a pre-vaccination titer below the LLOQ and a postvaccination titer ≥4xLLOQ; or a pre-vaccination titer ≥LLOQ and a ≥4-fold increase in post-vaccination titer.
Time frame: Day 29
Groups 1a and 2a: Number of Participants With SARS-CoV-2 Neutralizing Antibody Against Omicron XBB.1.5 Subvariant Titer ≥ LLOQ at Days 1 and 29
Time frame: Days 1 and 29
Groups 1a and 3a: GMTs of HI Assay Titers Against Influenza Vaccine Strains at Days 1 and 29
Vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata.
Time frame: Days 1 and 29
Groups 1a and 3a: GMFR of HI Assay Titers Against Influenza Vaccine Strains at Day 29
Vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata. GMFR is reported as a ratio to Day 1.
Time frame: Day 29
Groups 1a and 3a: Number of Participants With Seroconversion of HI Assay Titers Against Influenza Vaccine Strains at Day 29
Seroconversion was defined as either a pre-vaccination titer below the LLOQ and a postvaccination titer ≥4xLLOQ; or a pre-vaccination titer ≥LLOQ and a ≥4-fold increase in post-vaccination titer. Vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata.
Time frame: Day 29
Groups 1a and 3a: Number of Participants With HI Titer ≥1:40 at Days 1 and 29
Vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata.
Time frame: Days 1 and 29
Groups 1b and 2b: GMTs of SARS-CoV-2 Neutralizing Antibodies Against Omicron XBB.1.5 Subvariant at Days 1, 29 and 181
Time frame: Group 1b: Days 1 and 29, Group 2b: Days 1, 29 and 181
Groups 1b and 2b: GMFRs of SARS-CoV-2 Neutralizing Antibodies Against Omicron XBB.1.5 Subvariant at Days 29 and 181
GMFR is reported as a ratio to Day 1.
Time frame: Group 1b: Day 29 and Group 2b: Days 29 and 181
Groups 1b and 2b: Number of Participants With Seroconversion of SARS-CoV-2 Neutralizing Antibodies Against Omicron XBB.1.5 Subvariant at Day 29
Seroconversion was defined as either a pre-vaccination titer below the LLOQ and a postvaccination titer ≥4xLLOQ; or a pre-vaccination titer ≥LLOQ and a ≥4-fold increase in post-vaccination titer.
Time frame: Day 29
Groups 1b and 2b: Number of Participants With SARS-CoV-2 Neutralizing Antibody Against Omicron XBB.1.5 Subvariant Titer ≥ LLOQ at Days 1 and 29
Time frame: Days 1 and 29
Groups 1b and 3b: GMTs of HI Assay Titers Against Influenza Vaccine Strains at Days 1 and 29
Vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata.
Time frame: Days 1 and 29
Groups 1b and 3b: GMFRs of of HI Assay Titers Against Influenza Vaccine Strains at Day 29
Vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata. GMFR is reported as a ratio to Day 1.
Time frame: Day 29
Groups 1b and 3b: Number of Participants With Seroconversion of HI Assay Titers Against Influenza Vaccine Strains at Day 29
Seroconversion was defined as either a pre-vaccination titer below the LLOQ and a postvaccination titer ≥4xLLOQ; or a pre-vaccination titer ≥LLOQ and a ≥4-fold increase in post-vaccination titer. Vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata.
Time frame: Day 29
Groups 1b and 3b: Number of Participants With HI Titer ≥1:40 at Days 1 and 29
Vaccine strains analyzed for this outcome measure were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata.
Time frame: Days 1 and 29
Number of Participants With Local and Systemic Adverse Events (AEs)
Systemic AEs: fatigue, headache, myalgia, arthralgia, nausea, dizziness, chills, and fever. Solicited local (injection site) AEs: injection site pain, erythema, and swelling. A summary of serious and all other non-serious adverse events regardless of causality is located in the Reported Adverse Events module.
Time frame: Day 8 and Day 36 (up to 7 days after each study vaccination)
Number of Participants With Unsolicited AEs
An unsolicited AE was an AE that was not listed as 'solicited' and was defined as any spontaneously occurring AE (serious and non-serious). Potential unsolicited AEs may have been medically attended (defined as symptoms or illnesses requiring hospitalization, or emergency room visit, or visit to/by a healthcare provider) or were of concern to the participants. A summary of serious and all other non-serious adverse events regardless of causality is located in the Reported Adverse Events module.
Time frame: Up to Day 29 (Up to 28 days after first study vaccination) and up to Day 57 (28 days after second study vaccination)
Number of Participants With Serious Adverse Events (SAEs), AEs Leading to Early Termination From Study, Medically Attended Adverse Event (MAAEs), and Adverse Event of Special Interest (AESIs)
SAEs were defined as any event that resulted in death, was life threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in a persistent or significant incapacity or substantial disruption of the ability to conduct normal life functions, a congenital anomaly or birth defect, or was an important medical event. A MAAE was an AE that led to an unscheduled visit (including a telemedicine visit) to a healthcare practitioner. AESIs were defined as AEs potentially associated with Coronavirus Disease 2019 (COVID-19) and COVID-19 vaccines. Number of participants with AEs leading to early termination included AEs leading to death. A summary of serious and all other non-serious adverse events regardless of causality is located in the Reported Adverse Events module.
Time frame: Day 1 up to Day 181
| Milestone | Cohort A Group 1a: ARCT-2303+ Quadrivalent Influenza Vaccine (QIV) + Placebo | Cohort A Group 2a: ARCT-2303 + Placebo + QIV | Cohort A Group 3a: QIV + Placebo + ARCT-2303 | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 2b: ARCT-2303 + Placebo + aQIV | Cohort B Group 3b: aQIV + Placebo + ARCT-2303 | ARCT-154-J01 (Historical Control) |
|---|---|---|---|---|---|---|---|
| Started | 408 | 406 | 405 | 99 | 98 | 98 | 385 |
| Received dose 1 | 403 | 403 | 398 | 99 | 98 | 98 | 385 |
| Received dose 2 | 393 | 394 | 390 | 95 | 97 | 96 | 0 |
| Completed | 392 | 387 | 389 | 97 | 98 | 97 | 385 |
| Not completed | 16 | 19 | 16 | 2 | 0 | 1 | 0 |
| Withdrew: Death | 0 | 0 | 0 | 0 | 0 | 1 | 0 |
| Withdrew: Other than specified | 1 | 0 | 4 | 0 | 0 | 0 | 0 |
| Withdrew: Withdrawal by subject | 4 | 8 | 4 | 2 | 0 | 0 | 0 |
| Withdrew: Lost to follow-up | 11 | 10 | 8 | 0 | 0 | 0 | 0 |
| Withdrew: Adverse event | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
| Titer | Cohort A Group 2a: ARCT-2303 + Placebo + QIV and Cohort B Group 2b: ARCT-2303 + Placebo + aQIV | ARCT-154-J01 (Historical Control) |
|---|---|---|
| Groups 2a and 2b and ARCT-154-J01 Historical Control: Geometric Mean Titers (GMT) of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Neutralizing Antibody Titers Against Omicron XBB.1.5 Subvariant at Day 29 | 718 (652 to 791) | 263 (236 to 293) |
Seroconversion was defined as either a pre-vaccination titer below the lower limit of quantitation (LLOQ) and a postvaccination titer ≥4xLLOQ; or a pre-vaccination titer ≥LLOQ and a ≥4-fold increase in post-vaccination titer.
| Participants | Cohort A Group 2a: ARCT-2303 + Placebo + QIV and Cohort B Group 2b: ARCT-2303 + Placebo + aQIV | ARCT-154-J01 (Historical Control) |
|---|---|---|
| Groups 2a and 2b and ARCT-154-J01 Historical Control: Number of Participants With Seroconversion to SARS-CoV-2 Neutralizing Antibody Against Omicron XBB.1.5 Subvariant at Day 29 | 349 | 175 |
Influenza vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata.
| titers | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 3a: QIV + Placebo + ARCT-2303 |
|---|---|---|
| A/H1N1 | 338 (289 to 395) | 354 (304 to 413) |
| A/H3N2 | 280 (242 to 325) | 269 (232 to 311) |
| B/Victoria | 109 (92 to 129) | 99 (84 to 117) |
| B/Yamagata | 123 (111 to 137) | 112 (101 to 125) |
| titers | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 2a: ARCT-2303 + Placebo + QIV |
|---|---|---|
| Groups 1a and 2a: Adjusted GMTs of SARS-CoV-2 Neutralizing Antibody Against Omicron XBB.1.5 Subvariant at Day 29 | 768 (680 to 867) | 954 (844 to 1077) |
| titers | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 2a: ARCT-2303 + Placebo + QIV |
|---|---|---|
| Day 1 | 118 (103 to 135) | 140 (123 to 169) |
| Day 29 | 789 (708 to 880) | 1072 (957 to 1199) |
| Day 181 | — | 794 (653 to 967) |
GMFR is reported as a ratio to Day 1.
| ratio | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 2a: ARCT-2303 + Placebo + QIV |
|---|---|---|
| Day 29 | 6.7 (6.0 to 7.5) | 7.7 (6.8 to 8.6) |
| Day 181 | — | 5.3 (4.2 to 6.7) |
Seroconversion was defined as either a pre-vaccination titer below the LLOQ and a postvaccination titer ≥4xLLOQ; or a pre-vaccination titer ≥LLOQ and a ≥4-fold increase in post-vaccination titer.
| Participants | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 2a: ARCT-2303 + Placebo + QIV |
|---|---|---|
| Groups 1a and 2a: Number of Participants With Seroconversion of SARS-CoV-2 Neutralizing Antibodies Against Omicron XBB.1.5 Subvariant at Day 29 | 242 | 279 |
| Participants | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 2a: ARCT-2303 + Placebo + QIV |
|---|---|---|
| Day 1 | 331 | 344 |
| Day 29 | 375 | 378 |
Vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata.
| titer | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 3a: QIV + Placebo + ARCT-2303 |
|---|---|---|
| A/H1N1 Day 1 | 38 (33 to 44) | 37 (32 to 43) |
| A/H1N1 Day 29 | 429 (374 to 493) | 433 (381 to 491) |
| A/H3N2 Day 1 | 32 (28 to 37) | 36 (31 to 42) |
| A/H3N2 Day 29 | 331 (291 to 378) | 334 (295 to 377) |
| B/Victoria Day 1 | 13 (12 to 15) | 15 (13 to 17) |
| B/Victoria Day 29 | 109 (95 to 125) | 102 (90 to 117) |
| B/Yamagata Day 1 | 29 (26 to 32) | 34 (30 to 37) |
| B/Yamagata Day 29 | 132 (119 to 145) | 126 (115 to 138) |
Vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata. GMFR is reported as a ratio to Day 1.
| ratio | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 3a: QIV + Placebo + ARCT-2303 |
|---|---|---|
| A/H1N1 | 11.2 (9.6 to 13.2) | 11.6 (9.8 to 13.6) |
| A/H3N2 | 10.3 (8.9 to 11.9) | 9.2 (8.0 to 10.6) |
| B/Victoria | 8.1 (7.0 to 9.4) | 6.9 (6.0 to 7.9) |
| B/Yamagata | 4.6 (4.1 to 5.1) | 3.7 (3.4 to 4.1) |
Seroconversion was defined as either a pre-vaccination titer below the LLOQ and a postvaccination titer ≥4xLLOQ; or a pre-vaccination titer ≥LLOQ and a ≥4-fold increase in post-vaccination titer. Vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata.
| Participants | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 3a: QIV + Placebo + ARCT-2303 |
|---|---|---|
| A/H1N1 | 267 | 259 |
| A/H3N2 | 266 | 266 |
| B/Victoria | 233 | 215 |
| B/Yamagata | 197 | 167 |
Vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata.
| Participants | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 3a: QIV + Placebo + ARCT-2303 |
|---|---|---|
| A/H1N1 Day 1 | 197 | 195 |
| A/H1N1 Day 29 | 354 | 367 |
| A/H3N2 Day 1 | 178 | 200 |
| A/H3N2 Day 29 | 361 | 364 |
| B/Victoria Day 1 | 73 | 83 |
| B/Victoria Day 29 | 299 | 294 |
| B/Yamagata Day 1 | 165 | 201 |
| B/Yamagata Day 29 | 345 | 347 |
| titer | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 2b: ARCT-2303 + Placebo + aQIV |
|---|---|---|
| Day 1 | 138 (106 to 180) | 206 (158 to 269) |
| Day 29 | 932 (742 to 1170) | 1420 (1126 to 1791) |
| Day 181 | — | 878 (738 to 1045) |
GMFR is reported as a ratio to Day 1.
| ratio | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 2b: ARCT-2303 + Placebo + aQIV |
|---|---|---|
| Day 29 | 6.8 (5.3 to 8.6) | 6.9 (5.4 to 8.8) |
| Day 181 | — | 4.3 (3.2 to 5.7) |
Seroconversion was defined as either a pre-vaccination titer below the LLOQ and a postvaccination titer ≥4xLLOQ; or a pre-vaccination titer ≥LLOQ and a ≥4-fold increase in post-vaccination titer.
| Participants | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 2b: ARCT-2303 + Placebo + aQIV |
|---|---|---|
| Groups 1b and 2b: Number of Participants With Seroconversion of SARS-CoV-2 Neutralizing Antibodies Against Omicron XBB.1.5 Subvariant at Day 29 | 66 | 70 |
| Participants | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 2b: ARCT-2303 + Placebo + aQIV |
|---|---|---|
| Day 1 | 84 | 90 |
| Day 29 | 92 | 95 |
Vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata.
| titers | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 3b: aQIV + Placebo + ARCT-2303 |
|---|---|---|
| A/H1N1 Day 1 | 115 (83 to 160) | 109 (78 to 153) |
| A/H1N1 Day 29 | 1064 (827 to 1369) | 961 (773 to 1194) |
| A/H3N2 Day 1 | 78 (56 to 110) | 92 (68 to 127) |
| A/H3N2 Day 29 | 475 (368 to 613) | 453 (342 to 600) |
| B/Victoria Day 1 | 20 (15 to 26) | 29 (20 to 41) |
| B/Victoria Day 29 | 121 (91 to 160) | 132 (98 to 178) |
| B/Yamagata Day 1 | 25 (19 to 34) | 27 (20 to 35) |
| B/Yamagata Day 29 | 138 (108 to 176) | 132 (102 to 170) |
Vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata. GMFR is reported as a ratio to Day 1.
| ratio | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 3b: aQIV + Placebo + ARCT-2303 |
|---|---|---|
| A/H1N1 | 9.2 (6.4 to 13.4) | 8.8 (6.1 to 12.6) |
| A/H3N2 | 6.0 (4.4 to 8.4) | 4.9 (3.6 to 6.7) |
| B/Victoria | 6.2 (4.4 to 8.5) | 4.6 (3.4 to 6.1) |
| B/Yamagata | 5.5 (4.0 to 7.6) | 5.0 (3.8 to 6.5) |
Seroconversion was defined as either a pre-vaccination titer below the LLOQ and a postvaccination titer ≥4xLLOQ; or a pre-vaccination titer ≥LLOQ and a ≥4-fold increase in post-vaccination titer. Vaccine strains were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata.
| Participants | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 3b: aQIV + Placebo + ARCT-2303 |
|---|---|---|
| A/H1N1 | 59 | 59 |
| A/H3N2 | 50 | 42 |
| B/Victoria | 47 | 45 |
| B/Yamagata | 48 | 47 |
Vaccine strains analyzed for this outcome measure were A/H1N1, A/H3N2, B/Victoria, and B/Yamagata.
| Participants | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 3b: aQIV + Placebo + ARCT-2303 |
|---|---|---|
| A/H1N1 Day 1 | 75 | 71 |
| A/H1N1 Day 29 | 92 | 93 |
| A/H3N2 Day 1 | 62 | 70 |
| A/H3N2 Day 29 | 90 | 91 |
| B/Victoria Day 1 | 32 | 41 |
| B/Victoria Day 29 | 76 | 80 |
| B/Yamagata Day 1 | 37 | 40 |
| B/Yamagata Day 29 | 84 | 81 |
Systemic AEs: fatigue, headache, myalgia, arthralgia, nausea, dizziness, chills, and fever. Solicited local (injection site) AEs: injection site pain, erythema, and swelling. A summary of serious and all other non-serious adverse events regardless of causality is located in the Reported Adverse Events module.
| Participants | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 2a: ARCT-2303 + Placebo + QIV | Cohort A Group 3a: QIV + Placebo + ARCT-2303 | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 2b: ARCT-2303 + Placebo + aQIV | Cohort B Group 3b: aQIV + Placebo + ARCT-2303 |
|---|---|---|---|---|---|---|
| Solicited Local AE after First Vaccination (up to Day 8) | 283 | 296 | 167 | 41 | 30 | 20 |
| Solicited Systemic AE after First Vaccination (up to Day 8) | 255 | 258 | 162 | 36 | 23 | 25 |
| Solicited Local AE after Second Vaccination (up to Day 36) | 38 | 146 | 263 | 5 | 15 | 22 |
| Solicited Systemic AE after Second Vaccination (up to Day 36) | 105 | 118 | 217 | 14 | 15 | 17 |
An unsolicited AE was an AE that was not listed as 'solicited' and was defined as any spontaneously occurring AE (serious and non-serious). Potential unsolicited AEs may have been medically attended (defined as symptoms or illnesses requiring hospitalization, or emergency room visit, or visit to/by a healthcare provider) or were of concern to the participants. A summary of serious and all other non-serious adverse events regardless of causality is located in the Reported Adverse Events module.
| Participants | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 2a: ARCT-2303 + Placebo + QIV | Cohort A Group 3a: QIV + Placebo + ARCT-2303 | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 2b: ARCT-2303 + Placebo + aQIV | Cohort B Group 3b: aQIV + Placebo + ARCT-2303 |
|---|---|---|---|---|---|---|
| Day 29 | 79 | 81 | 68 | 13 | 8 | 16 |
| Day 57 | 71 | 62 | 75 | 9 | 6 | 17 |
SAEs were defined as any event that resulted in death, was life threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in a persistent or significant incapacity or substantial disruption of the ability to conduct normal life functions, a congenital anomaly or birth defect, or was an important medical event. A MAAE was an AE that led to an unscheduled visit (including a telemedicine visit) to a healthcare practitioner. AESIs were defined as AEs potentially associated with Coronavirus Disease 2019 (COVID-19) and COVID-19 vaccines. Number of participants with AEs leading to early termination included AEs leading to death. A summary of serious and all other non-serious adverse events regardless of causality is located in the Reported Adverse Events module.
| Participants | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 2a: ARCT-2303 + Placebo + QIV | Cohort A Group 3a: QIV + Placebo + ARCT-2303 | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 2b: ARCT-2303 + Placebo + aQIV | Cohort B Group 3b: aQIV + Placebo + ARCT-2303 |
|---|---|---|---|---|---|---|
| SAEs | 7 | 5 | 6 | 2 | 3 | 5 |
| AEs Leading to Early Termination from Study | 0 | 1 | 0 | 0 | 0 | 1 |
| MAAEs | 103 | 95 | 100 | 19 | 13 | 19 |
| AESIs | 1 | 1 | 3 | 1 | 1 | 1 |
Collected over Day 1 up to Day 181. Non-serious events are listed at a 2.5% frequency threshold.
| Group | Deaths | Serious | Other |
|---|---|---|---|
| Cohort A Group 1a: ARCT-2303+ QIV + Placebo | 0/403 (0%) | 7/403 (1.7%) | 65/403 (16.1%) |
| Cohort A Group 2a: ARCT-2303 + Placebo + QIV | 0/403 (0%) | 5/403 (1.2%) | 59/403 (14.6%) |
| Cohort A Group 3a: QIV + Placebo + ARCT-2303 | 0/398 (0%) | 6/398 (1.5%) | 49/398 (12.3%) |
| Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | 0/99 (0%) | 2/99 (2%) | 6/99 (6.1%) |
| Cohort B Group 2b: ARCT-2303 + Placebo + aQIV | 0/98 (0%) | 3/98 (3.1%) | 0/98 (0%) |
| Cohort B Group 3b: aQIV + Placebo + ARCT-2303 | 1/98 (1%) | 5/98 (5.1%) | 14/98 (14.3%) |
| Event | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 2a: ARCT-2303 + Placebo + QIV | Cohort A Group 3a: QIV + Placebo + ARCT-2303 | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 2b: ARCT-2303 + Placebo + aQIV | Cohort B Group 3b: aQIV + Placebo + ARCT-2303 |
|---|---|---|---|---|---|---|
| Acute myocardial infarctionCardiac disorders | 0/403 | 0/403 | 0/398 | 1/99 | 1/98 | 0/98 |
| Cardiogenic shockCardiac disorders | 0/403 | 0/403 | 0/398 | 0/99 | 0/98 | 1/98 |
| MyopericarditisCardiac disorders | 0/403 | 0/403 | 0/398 | 0/99 | 1/98 | 0/98 |
| Angle closure glaucomaEye disorders | 0/403 | 0/403 | 0/398 | 0/99 | 0/98 | 1/98 |
| Malignant glaucomaEye disorders | 0/403 | 0/403 | 0/398 | 0/99 | 0/98 | 1/98 |
| Abdominal wall haematomaGastrointestinal disorders | 0/403 | 0/403 | 0/398 | 0/99 | 1/98 | 0/98 |
| CellulitisInfections and infestations | 0/403 | 0/403 | 0/398 | 0/99 | 0/98 | 1/98 |
| Dengue feverInfections and infestations | 0/403 | 0/403 | 0/398 | 0/99 | 1/98 | 0/98 |
| Cataract traumaticInjury, poisoning and procedural complications | 0/403 | 0/403 | 0/398 | 0/99 | 0/98 | 1/98 |
| Radius fractureInjury, poisoning and procedural complications | 0/403 | 0/403 | 0/398 | 0/99 | 0/98 | 1/98 |
| Event | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 2a: ARCT-2303 + Placebo + QIV | Cohort A Group 3a: QIV + Placebo + ARCT-2303 | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 2b: ARCT-2303 + Placebo + aQIV | Cohort B Group 3b: aQIV + Placebo + ARCT-2303 |
|---|---|---|---|---|---|---|
| Upper respiratory tract infectionInfections and infestations | 43/403 | 38/403 | 31/398 | 3/99 | 0/98 | 0/98 |
| COVID-19Infections and infestations | 22/403 | 21/403 | 18/398 | 3/99 | 0/98 | 0/98 |
| HypertensionVascular disorders | 0/403 | 0/403 | 0/398 | 0/99 | 0/98 | 5/98 |
| DiarrhoeaGastrointestinal disorders | 0/403 | 0/403 | 0/398 | 0/99 | 0/98 | 3/98 |
| DyslipidaemiaMetabolism and nutrition disorders | 0/403 | 0/403 | 0/398 | 0/99 | 0/98 | 3/98 |
| Hypertensive urgencyVascular disorders | 0/403 | 0/403 | 0/398 | 0/99 | 0/98 | 3/98 |
Intent-to-Treat (ITT), all participants who received at least one dose of a study vaccine in this study. Data are also reported for participants from study ARCT-154-J01 (historical control group), which included participants from ARCT-154-J01 who received ARCT-154 booster vaccine, provided evaluable pre-/post-vaccination blood samples, and did not have SARS-CoV-2 infection/protocol deviations that impacted immunogenicity assessment. Participants were analyzed according to the vaccine assigned.
| Age, Continuous(years) | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 2a: ARCT-2303 + Placebo + QIV | Cohort A Group 3a: QIV + Placebo + ARCT-2303 | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 2b: ARCT-2303 + Placebo + aQIV | Cohort B Group 3b: aQIV + Placebo + ARCT-2303 | ARCT-154-J01 (Historical Control) | Total |
|---|---|---|---|---|---|---|---|---|
| Mean | 37.7 ± 12.0 | 36.8 ± 12.1 | 39.2 ± 11.9 | 69.6 ± 5.3 | 70.4 ± 5.4 | 70.4 ± 4.9 | 45.3 ± 11.9 | 44.2 ± 16.9 |
| Sex: Female, Male(Participants) | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 2a: ARCT-2303 + Placebo + QIV | Cohort A Group 3a: QIV + Placebo + ARCT-2303 | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 2b: ARCT-2303 + Placebo + aQIV | Cohort B Group 3b: aQIV + Placebo + ARCT-2303 | ARCT-154-J01 (Historical Control) | Total |
|---|---|---|---|---|---|---|---|---|
| Female | 259 | 255 | 243 | 64 | 68 | 63 | 228 | 1180 |
| Male | 144 | 148 | 155 | 35 | 30 | 35 | 157 | 704 |
| Ethnicity (NIH/OMB)(Participants) | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 2a: ARCT-2303 + Placebo + QIV | Cohort A Group 3a: QIV + Placebo + ARCT-2303 | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 2b: ARCT-2303 + Placebo + aQIV | Cohort B Group 3b: aQIV + Placebo + ARCT-2303 | ARCT-154-J01 (Historical Control) | Total |
|---|---|---|---|---|---|---|---|---|
| Hispanic or Latino | 65 | 67 | 64 | 23 | 15 | 21 | 0 | 255 |
| Not Hispanic or Latino | 333 | 333 | 332 | 76 | 83 | 77 | 385 | 1619 |
| Unknown or Not Reported | 5 | 3 | 2 | 0 | 0 | 0 | 0 | 10 |
| Race (NIH/OMB)(Participants) | Cohort A Group 1a: ARCT-2303+ QIV + Placebo | Cohort A Group 2a: ARCT-2303 + Placebo + QIV | Cohort A Group 3a: QIV + Placebo + ARCT-2303 | Cohort B Group 1b: ARCT-2303 + Adjuvanted QIV (aQIV) + Placebo | Cohort B Group 2b: ARCT-2303 + Placebo + aQIV | Cohort B Group 3b: aQIV + Placebo + ARCT-2303 | ARCT-154-J01 (Historical Control) | Total |
|---|---|---|---|---|---|---|---|---|
| American Indian or Alaska Native | 18 | 11 | 16 | 4 | 6 | 5 | 0 | 60 |
| Asian | 150 | 159 | 177 | 69 | 77 | 68 | 385 | 1085 |
| Native Hawaiian or Other Pacific Islander | 7 | 3 | 2 | 0 | 0 | 0 | 0 | 12 |
| Black or African American | 1 | 0 | 2 | 0 | 0 | 0 | 0 | 3 |
| White | 179 | 173 | 158 | 9 | 8 | 10 | 0 | 537 |
| More than one race | 14 | 15 | 13 | 7 | 2 | 3 | 0 | 54 |
| Unknown or Not Reported | 34 | 42 | 30 | 10 | 5 | 12 | 0 | 133 |
PDFs hosted by the registry, ClinicalTrials.gov.
Plan to share: No
Ran from Mar 2024 to primary completion in Oct 2024, 6 months.
Results were first posted in Dec 2025, 1 year 2 months after primary completion.
Of 168 industry-sponsored phase 3 interventional studies under COVID-19, half reached primary completion within 8 months of starting (the median), counting those still running; a quarter within 4 and three quarters within 16. This study's 6 months is below that.
Counting every sponsor, half of 453 studies reached it within 9 months; a quarter within 4 and three quarters within 17.
How these figures are worked out, and which studies are left out of them.
This study is completed, as verified in Nov 2025. You cannot join it, but the record below documents what was studied.
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Arcturus Therapeutics, Inc.