COVID-19Phase 1/2NCT05037097

A Trial Evaluating the Safety and Immunogenicity of 3 COVID-19 SARS-CoV-2 RNA Vaccines in Healthy Adults

A Phase 1/2 study testing ARCT-165, ARCT-154 and ARCT-021 in people with COVID-19 and SARS-CoV-2 Infection, run by Arcturus Therapeutics, Inc. at 4 sites in 3 countries.

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

This is a Phase 1/2, randomized, observer-blind study in healthy adults. The study will evaluate the safety, reactogenicity, and immunogenicity of 3 SARS-CoV-2 self-amplifying RNA vaccine candidates against COVID-19 in adults previously vaccinated and not previously vaccinated against SARS-CoV-2. Read more about this study

Who is it for?: Ages 21 to 80 yearsHealthy volunteers can take part
Conditions the study is for: COVID-19, SARS-CoV-2 Infection, Corona Virus Infection
What is being tested?: ARCT-165, ARCT-154 and ARCT-021
Could I receive a placebo?: No, everyone receives an active treatment
How many people: 72 participants
Where: 4 sitesin 3 countries
Study dates: 30 Aug 2021to 19 Dec 2023
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 21 to 80 years
All sexes
Healthy volunteers accepted
Adult, Older adult

Who may be able to join

Individuals who:
Are able to provide consent
Agree to comply with all study visits and procedures
Are willing and able to adhere to study restrictions
Are sexually active and willing to adhere to contraceptive requirements
Are male, female, or transgender ≥21 to ≤80 years of age
For the previously vaccinated groups only, received 2 doses of SARS-CoV-2 vaccine 5 months or longer prior to study enrollment

Who cannot join

Individuals who:
For the unvaccinated groups only, previously received any investigational or authorized MERS-CoV, SARS-CoV, and SARS-CoV-2 vaccines (including ARCT-021)
For the previously vaccinated groups only, previously received BNT162b2 but have not received 2 doses within at least 5 months prior to study enrollment
Are planning to receive other COVID-19 vaccines during the study period
Recently received other vaccines
Have a fever or are feeling sick close to the time of the first study vaccination

Show all 24Show fewer

Have a known history of COVID-19 disease or asymptomatic SARS-CoV-2 infection
Are pregnant or breastfeeding
Have had a severe reaction to previous vaccines
Have a severe or uncontrolled disease(s) that may interfere with the interpretation of the study
Have some respiratory diseases
Have some significant heart diseases
Have some neurological conditions
Have sickle cell disease or some other blood disorders
Have had a major surgery within the past 6 months
Have a history of chronic liver disease
Have a history of autoimmune disease or immunodeficiency
Have received allergy injections, interferon, immunomodulators, cytotoxic drugs or other similar toxic drugs.
Have received blood products
Have a positive test for hepatitis B or C or human immunodeficiency virus
Have uncontrolled hypertension
Have had cancer except for cancers that were treated and that have low risk of returning
Are obese
Are Investigator site staff members, employees of Arcturus or the contract research organization (CRO) directly involved in the conduct of the study, or site staff members otherwise supervised by the Investigator or immediate family members of any of the previously mentioned individuals

Trial locations and contacts

4 sites in 3 countries.

Country

City, postcode or hospital

4 sites in 3 countries

United States2 sites

Arcturus Investigational Site 201
Kansas City, Missouri, 64114
Arcturus Investigational Site 202
Wichita, Kansas, 67207

Other trials in United States

Singapore1 site

Arcturus Investigational Site 101
Singapore, 169608

Other trials in Singapore

South Africa1 site

Arcturus Investigational Site 301
Diepkloof, Soweto, 1862

Other trials in South Africa

About this study

Official title: A Phase 1/2 Randomized, Observer-Blind Study of the Safety, Reactogenicity, and Immunogenicity of 3 SARS-CoV-2 RNA Vaccine Candidates in Adults Previously Vaccinated and Not Previously Vaccinated Against SARS-CoV-2

Read the detailed description

The study will initially enroll approximately 72 adult participants into 2 cohorts (A and B). Cohort A is further sub-divided into two sub-cohorts which include 12 participants who are seronegative, not previously vaccinated at screening (Sub-cohort A1) and 24 participants who are seropositive, not previously vaccinated at screening (Sub-cohort A2).

Within the first cohort (Cohort A), Sub-cohort A1 will include a total of 12 adult participants ≥21 to ≤65 years of age who have not been previously vaccinated with a SARS-CoV-2 vaccine. Sub-cohort A2 will include a total of 24 adult participants ≥21 to ≤65 years of age who have not been previously vaccinated with a SARS-CoV-2 vaccine. Study vaccines will be given as 2 doses separated by 28 days.

The second cohort (Cohort B) will include a total of 36 adult participants ≥21 to ≤65 years of age who have been previously vaccinated (5 months or longer prior to study enrollment) with SARS-CoV-2 vaccine. Study vaccines will be given as single doses.

Additional cohorts may increase the age range of participants up to 80 years of age.

Conditions: COVID-19, SARS-CoV-2 Infection, Corona Virus Infection
Being tested: ARCT-165, ARCT-154, ARCT-021
Keywords: SARS-CoV-2 Vaccine, Coronavirus Virus Diseases, RNA COVID-19, COVID-19 Vaccine Arcturus, Self Amplifying RNA Vaccine, Variants of Concern
Medical subject headings: COVID-19, Coronavirus Infections

What participants receive

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

ARCT-165Biological
Dose 3
ARCT-154Biological
Dose 2
ARCT-021Biological
Dose 1

Study groups in NCT05037097
Study group	Role	What they receive
Study Group 1, Adult Participants Seronegative, Not Previously Vaccinated randomized to ARCT-165	Experimental	Participants will receive one dose of ARCT-165 on Day 1 and one dose of ARCT-165 on Day 29 Receives: Biological: ARCT-165
Study Group 2, Adult Participants Seronegative, Not Previously Vaccinated randomized to ARCT-154	Experimental	Participants will receive one dose of ARCT-154 on Day 1 and one dose of ARCT-154 on Day 29 Receives: Biological: ARCT-154
Study Group 3, Adult Participants Seronegative, Not Previously Vaccinated to receive ARCT-021	Experimental	Participants will receive one dose of ARCT-021 on Day 1 and one dose of ARCT-021 on Day 29 Receives: Biological: ARCT-021
Study Group 4, Adult Participants Seropositive, Not Previously Vaccinated to receive ARCT-021	Experimental	Participants will receive one dose of ARCT-021 on Day 1 and one dose of ARCT-021 on Day 29 Receives: Biological: ARCT-021
Study Group 5, Adult Participants Seropositive, Not Previously Vaccinated randomized to ARCT-154	Experimental	Participants will receive one dose of ARCT-154 on Day 1 and one dose of ARCT-154 on Day 29 Receives: Biological: ARCT-154
Study Group 6, Adult Participants Previously Vaccinated randomized to receive ARCT-165	Experimental	Participants will receive one dose of ARCT-165 on Day 1 Receives: Biological: ARCT-165
Study Group 7, Adult Participants Previously Vaccinated randomized to receive ARCT-154	Experimental	Participants will receive one dose of ARCT-154 on Day 1 Receives: Biological: ARCT-154
Study Group 8, Adult Participants Previously Vaccinated randomized to receive ARCT-021	Experimental	Participants will receive one dose of ARCT-021 on Day 1 Receives: Biological: ARCT-021

What is being measured

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

Number of Participants Reporting Solicited Local or Systemic Adverse Events (AEs)
Solicited local AEs were defined as injection site erythema, injection site pain, injection site induration, and injection site tenderness. Solicited systemic AEs were defined as arthralgia, chills, diarrhea, dizziness, fatigue, fever (categorized by measured body temperature), headache, myalgia, nausea and vomiting. Data are reported for the number of participants with solicited local and solicited systemic AEs. A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section.
Measured: Up to Day 8 (7 days after first vaccine administration for Cohorts A1, A2 and B), and up to Day 36 (7 days after second vaccine administration for Cohorts A1 and A2)
Number of Participants Reporting Unsolicited AEs
Unsolicited AEs were defined as any spontaneously reported or discovered AE. Data are reported for the number of participants with unsolicited AEs. A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section.
Measured: Up to Day 29 (28 days after vaccine administration for Cohort B), and up to Day 57 (up to 28 days after each vaccine administration for Cohorts A1 and A2)
Number of Participants Reporting Medically Attended Adverse Events (MAAEs), AEs Leading to Discontinuation From Study Vaccine/Study Withdrawal, or Serious Adverse Events (SAEs)
An MAAE was an AE that led to an unscheduled visit (including a telemedicine visit) with a health care provider (HCP) (e.g., nurse, nurse practitioner, physician's assistant, physician), including visits to a study site for unscheduled assessments (e.g., rash assessment, abnormal laboratory follow up, coronavirus disease 2019 [COVID-19]) and visits to HCPs external to the study site (e.g., urgent care, primary care physician). An SAE was defined as any event that resulted in death, was immediately life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, or was a congenital anomaly/birth defect. A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section.
Measured: Through Final Visit (365 days after last study vaccine dose); up to a maximum of approximately 394 days
Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2) Serum Neutralizing Antibody Levels, Expressed as Geometric Mean Concentration (GMC)
Blood samples were collected to assess participants' immune response. GMC data are reported for the pseudoviral D614G variant. Data are reported in international units per milliliter (IU/mL).
Measured: Baseline, Days 29, 57, 209, Final Visit (approx. Day 394) for Cohorts A1 and A2; Baseline, Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
SARS-CoV-2 Serum Neutralizing Antibody Levels, Expressed as GMC
Blood samples were collected to assess participants' immune response. GMC data are reported for the pseudoviral B.1.351 (beta) variant. Data are reported in arbitrary units per milliliter (AU/mL).
Measured: Baseline, Days 29, 57, 209, Final Visit (approx. Day 394) for Cohorts A1 and A2; Baseline, Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
SARS-CoV-2 Serum Neutralizing Antibody Levels, Expressed as Geometric Mean Fold Rise (GMFR)
Blood samples were collected to assess participants' immune response. GMFR data are reported for the pseudoviral D614G variant.
Measured: Days 29, 57, 209, Final Visit (approx. Day 394) for Cohorts A1 and A2, and Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
SARS-CoV-2 Serum Neutralizing Antibody Levels, Expressed as GMFR
Blood samples were collected to assess participants' immune response. GMFR data are reported for the pseudoviral B.1.351 (beta) variant.
Measured: Days 29, 57, 209, Final Visit (approx. Day 394) for Cohorts A1 and A2, and Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
Number of Participants Achieving Greater Than or Equal to 4-fold Rise From Before Vaccination in SARS-CoV-2 Serum Neutralizing Antibody Levels (Pseudoviral D614G Variant)
Blood samples were collected to assess participants' immune response. Data are reported for the pseudoviral D614G variant.
Measured: Days 29, 57, 209, Final Visit (approx. Day 394) for Cohorts A1 and A2, and Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
Number of Participants Achieving Greater Than or Equal to 4-fold Rise From Before Vaccination in SARS-CoV-2 Serum Neutralizing Antibody Levels (Pseudoviral B.1.351 [Beta] Variant)
Blood samples were collected to assess participants' immune response. Data are reported for the pseudoviral B.1.351 (beta) variant.
Measured: Days 29, 57, 209, Final Visit (approx. Day 394) for Cohorts A1 and A2, and Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
GMC Ratio (ARCT-165 vs ARCT-154 and ARCT-021 vs ARCT-154)
Blood samples were collected to assess participants' immune response. Data are reported for the pseudoviral D614G Variant, B.1.351 Variant, B.1.617.2 Variant, BA.1 Variant for the GMC ratio of ARCT-165 vs ARCT-154 and ARCT-021 vs ARCT-154. Data are reported for the ARCT-165 and ARCT-021 arms (vs ARCT-154 values).
Measured: Days 29, 57, 209, Final Visit (approx. Day 394) for Cohorts A1 and A2, and Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
GMC Ratio (ARCT-021 vs ARCT-165 Cohorts A1 and B)
Blood samples were collected to assess participants' immune response. Data are reported for the pseudoviral D614G Variant, B.1.351 Variant, B.1.617.2 Variant, BA.1 Variant for the GMC ratio of ARCT-021 vs ARCT-165. Data are reported for the ARCT-021 arm (vs ARCT-165 values).
Measured: Days 29, 57, 209, Final Visit (approx. Day 394) for Cohort A1, and Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
SARS-CoV-2 Full-length Spike and Receptor-binding Domain (RBD) Binding Antibody Levels, Expressed as GMCs
Spike binding antibody levels expressed as GMCs are reported for ancestral, D614G, and B.1.351 variants and RBD binding antibodies for ancestral strain.
Measured: Baseline and Day 57 for Cohorts A1 and A2, Baseline and Day 15 for Cohort B
Changes in SARS-CoV-2 Full-length Spike and RBD Binding Antibody Levels, Expressed as GMFRs
Spike binding antibody levels expressed as GMFRs are reported for ancestral, D614G, and B.1.351 variants and RBD binding antibody levels expressed as GMFR for ancestral strain.
Measured: Day 57 for Cohorts A1 and A2, Day 15 for Cohort B
Number of Participants Achieving Greater Than or Equal to 4-fold Rise From Before Vaccination in SARS-CoV-2 Full-length Spike and RBD Binding Antibody Levels
Data are reported for ancestral, D614G, and B.1.351 variants for Spike binding antibodies and ancestral for RBD binding antibodies.
Measured: Day 57 for Cohorts A1 and A2, Day 15 for Cohort B

Timeline

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

30 Aug 202119 Dec 2023

First posted8 Sep 2021
Study start30 Aug 2021
Primary completion19 Dec 2023
Study completion19 Dec 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 COVID-19Studies 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: Treatment
Allocation: Randomised
Intervention model: Parallel groups
Model description: The study will evaluate 3 investigational vaccines in parallel.
Masking: Quadruple blind
Who is masked: Participant, Care provider, Investigator, Outcomes assessor
Enrolment: 72 participants (actual)

IDs, dates and publications

ClinicalTrials.gov ID: NCT05037097
Sponsor's protocol ID: ARCT-165-01
Status last verified: Sep 2025
First submitted: 30 Aug 2021
Last updated: 15 Oct 2025
Results posted: Yes, on ClinicalTrials.gov
Data monitoring committee: No
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.

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?

See locations

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All COVID-19 trials

Study at a glance

From the registry record, last updated by the sponsor on 15 Oct 2025. Recruitment status is as the sponsor reported it: confirm with the study team.

Official title: A Phase 1/2 Randomized, Observer-Blind Study of the Safety, Reactogenicity, and Immunogenicity of 3 SARS-CoV-2 RNA Vaccine Candidates in Adults Previously Vaccinated and Not Previously Vaccinated Against SARS-CoV-2
ClinicalTrials.gov ID: NCT05037097
Acronym / sponsor ID: ARCT-165-01
Conditions: COVID-19, SARS-CoV-2 Infection, Corona Virus Infection
Keywords: SARS-CoV-2 Vaccine, Coronavirus Virus Diseases, RNA COVID-19, COVID-19 Vaccine Arcturus, Self Amplifying RNA Vaccine, Variants of Concern
Phase: Phase 1/2
Study type: Interventional
Recruitment status: Completed
Enrolment: 72 participants (actual)
Lead sponsor: Arcturus Therapeutics, Inc.Industry (pharma, biotech, devices)
Study start: 30 Aug 2021 (actual)
Primary completion: 19 Dec 2023 (actual)
Study completion: 19 Dec 2023 (actual)
First posted: 8 Sep 2021 (actual)
Results: Posted 15 Oct 2025

Clinical summary

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

Detailed description

Additional cohorts may increase the age range of participants up to 80 years of age.

Study design

Primary purpose: Treatment
Allocation: Randomised
Intervention model: Parallel groups
Masking: Quadruple blind (participant, care provider, investigator, outcomes assessor)
Number of arms: 8
Model description: The study will evaluate 3 investigational vaccines in parallel.

Arm	Type	Receives
Study Group 1, Adult Participants Seronegative, Not Previously Vaccinated randomized to ARCT-165	Experimental	Biological: ARCT-165Participants will receive one dose of ARCT-165 on Day 1 and one dose of ARCT-165 on Day 29
Study Group 2, Adult Participants Seronegative, Not Previously Vaccinated randomized to ARCT-154	Experimental	Biological: ARCT-154Participants will receive one dose of ARCT-154 on Day 1 and one dose of ARCT-154 on Day 29
Study Group 3, Adult Participants Seronegative, Not Previously Vaccinated to receive ARCT-021	Experimental	Biological: ARCT-021Participants will receive one dose of ARCT-021 on Day 1 and one dose of ARCT-021 on Day 29
Study Group 4, Adult Participants Seropositive, Not Previously Vaccinated to receive ARCT-021	Experimental	Biological: ARCT-021Participants will receive one dose of ARCT-021 on Day 1 and one dose of ARCT-021 on Day 29
Study Group 5, Adult Participants Seropositive, Not Previously Vaccinated randomized to ARCT-154	Experimental	Biological: ARCT-154Participants will receive one dose of ARCT-154 on Day 1 and one dose of ARCT-154 on Day 29
Study Group 6, Adult Participants Previously Vaccinated randomized to receive ARCT-165	Experimental	Biological: ARCT-165Participants will receive one dose of ARCT-165 on Day 1
Study Group 7, Adult Participants Previously Vaccinated randomized to receive ARCT-154	Experimental	Biological: ARCT-154Participants will receive one dose of ARCT-154 on Day 1
Study Group 8, Adult Participants Previously Vaccinated randomized to receive ARCT-021	Experimental	Biological: ARCT-021Participants will receive one dose of ARCT-021 on Day 1

Who may qualify

Ages: 21 to 80 years
Sex: All
Healthy volunteers: Accepted
Age groups: Adult, Older adult

Key inclusion criteria (7 listed)

Are able to provide consent
Agree to comply with all study visits and procedures
Are willing and able to adhere to study restrictions
Are sexually active and willing to adhere to contraceptive requirements
Are male, female, or transgender ≥21 to ≤80 years of age

Key exclusion criteria (24 listed)

For the unvaccinated groups only, previously received any investigational or authorized MERS-CoV, SARS-CoV, and SARS-CoV-2 vaccines (including ARCT-021)
For the previously vaccinated groups only, previously received BNT162b2 but have not received 2 doses within at least 5 months prior to study enrollment
Are planning to receive other COVID-19 vaccines during the study period
Recently received other vaccines
Have a fever or are feeling sick close to the time of the first study vaccination

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-165Dose 3	Biological	Study Group 1, Adult Participants Seronegative, Not Previously Vaccinated randomized to ARCT-165, Study Group 6, Adult Participants Previously Vaccinated randomized to receive ARCT-165
ARCT-154Dose 2	Biological	Study Group 2, Adult Participants Seronegative, Not Previously Vaccinated randomized to ARCT-154, Study Group 5, Adult Participants Seropositive, Not Previously Vaccinated randomized to ARCT-154, Study Group 7, Adult Participants Previously Vaccinated randomized to receive ARCT-154
ARCT-021Dose 1	Biological	Study Group 3, Adult Participants Seronegative, Not Previously Vaccinated to receive ARCT-021, Study Group 4, Adult Participants Seropositive, Not Previously Vaccinated to receive ARCT-021, Study Group 8, Adult Participants Previously Vaccinated randomized to receive ARCT-021

Primary outcome

Number of Participants Reporting Solicited Local or Systemic Adverse Events (AEs)
Time frame: Up to Day 8 (7 days after first vaccine administration for Cohorts A1, A2 and B), and up to Day 36 (7 days after second vaccine administration for Cohorts A1 and A2)
Solicited local AEs were defined as injection site erythema, injection site pain, injection site induration, and injection site tenderness. Solicited systemic AEs were defined as arthralgia, chills, diarrhea, dizziness, fatigue, fever (categorized by measured body temperature), headache, myalgia, nausea and vomiting. Data are reported for the number of participants with solicited local and solicited systemic AEs. A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section.
Number of Participants Reporting Unsolicited AEs
Time frame: Up to Day 29 (28 days after vaccine administration for Cohort B), and up to Day 57 (up to 28 days after each vaccine administration for Cohorts A1 and A2)
Unsolicited AEs were defined as any spontaneously reported or discovered AE. Data are reported for the number of participants with unsolicited AEs. A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section.
Number of Participants Reporting Medically Attended Adverse Events (MAAEs), AEs Leading to Discontinuation From Study Vaccine/Study Withdrawal, or Serious Adverse Events (SAEs)
Time frame: Through Final Visit (365 days after last study vaccine dose); up to a maximum of approximately 394 days
An MAAE was an AE that led to an unscheduled visit (including a telemedicine visit) with a health care provider (HCP) (e.g., nurse, nurse practitioner, physician's assistant, physician), including visits to a study site for unscheduled assessments (e.g., rash assessment, abnormal laboratory follow up, coronavirus disease 2019 [COVID-19]) and visits to HCPs external to the study site (e.g., urgent care, primary care physician). An SAE was defined as any event that resulted in death, was immediately life-threatening, required inpatient hospitalization or prolongation of existing hospitalization, resulted in persistent or significant disability/incapacity, or was a congenital anomaly/birth defect. A summary of all Serious Adverse Events and Other Adverse Events (nonserious) regardless of causality is located in the 'Reported Adverse Events' Section.
Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2) Serum Neutralizing Antibody Levels, Expressed as Geometric Mean Concentration (GMC)
Time frame: Baseline, Days 29, 57, 209, Final Visit (approx. Day 394) for Cohorts A1 and A2; Baseline, Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
Blood samples were collected to assess participants' immune response. GMC data are reported for the pseudoviral D614G variant. Data are reported in international units per milliliter (IU/mL).
SARS-CoV-2 Serum Neutralizing Antibody Levels, Expressed as GMC
Time frame: Baseline, Days 29, 57, 209, Final Visit (approx. Day 394) for Cohorts A1 and A2; Baseline, Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
Blood samples were collected to assess participants' immune response. GMC data are reported for the pseudoviral B.1.351 (beta) variant. Data are reported in arbitrary units per milliliter (AU/mL).
SARS-CoV-2 Serum Neutralizing Antibody Levels, Expressed as Geometric Mean Fold Rise (GMFR)
Time frame: Days 29, 57, 209, Final Visit (approx. Day 394) for Cohorts A1 and A2, and Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
Blood samples were collected to assess participants' immune response. GMFR data are reported for the pseudoviral D614G variant.
SARS-CoV-2 Serum Neutralizing Antibody Levels, Expressed as GMFR
Time frame: Days 29, 57, 209, Final Visit (approx. Day 394) for Cohorts A1 and A2, and Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
Blood samples were collected to assess participants' immune response. GMFR data are reported for the pseudoviral B.1.351 (beta) variant.
Number of Participants Achieving Greater Than or Equal to 4-fold Rise From Before Vaccination in SARS-CoV-2 Serum Neutralizing Antibody Levels (Pseudoviral D614G Variant)
Time frame: Days 29, 57, 209, Final Visit (approx. Day 394) for Cohorts A1 and A2, and Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
Blood samples were collected to assess participants' immune response. Data are reported for the pseudoviral D614G variant.
Number of Participants Achieving Greater Than or Equal to 4-fold Rise From Before Vaccination in SARS-CoV-2 Serum Neutralizing Antibody Levels (Pseudoviral B.1.351 [Beta] Variant)
Time frame: Days 29, 57, 209, Final Visit (approx. Day 394) for Cohorts A1 and A2, and Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
Blood samples were collected to assess participants' immune response. Data are reported for the pseudoviral B.1.351 (beta) variant.
GMC Ratio (ARCT-165 vs ARCT-154 and ARCT-021 vs ARCT-154)
Time frame: Days 29, 57, 209, Final Visit (approx. Day 394) for Cohorts A1 and A2, and Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
Blood samples were collected to assess participants' immune response. Data are reported for the pseudoviral D614G Variant, B.1.351 Variant, B.1.617.2 Variant, BA.1 Variant for the GMC ratio of ARCT-165 vs ARCT-154 and ARCT-021 vs ARCT-154. Data are reported for the ARCT-165 and ARCT-021 arms (vs ARCT-154 values).
GMC Ratio (ARCT-021 vs ARCT-165 Cohorts A1 and B)
Time frame: Days 29, 57, 209, Final Visit (approx. Day 394) for Cohort A1, and Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B
Blood samples were collected to assess participants' immune response. Data are reported for the pseudoviral D614G Variant, B.1.351 Variant, B.1.617.2 Variant, BA.1 Variant for the GMC ratio of ARCT-021 vs ARCT-165. Data are reported for the ARCT-021 arm (vs ARCT-165 values).
SARS-CoV-2 Full-length Spike and Receptor-binding Domain (RBD) Binding Antibody Levels, Expressed as GMCs
Time frame: Baseline and Day 57 for Cohorts A1 and A2, Baseline and Day 15 for Cohort B
Spike binding antibody levels expressed as GMCs are reported for ancestral, D614G, and B.1.351 variants and RBD binding antibodies for ancestral strain.
Changes in SARS-CoV-2 Full-length Spike and RBD Binding Antibody Levels, Expressed as GMFRs
Time frame: Day 57 for Cohorts A1 and A2, Day 15 for Cohort B
Spike binding antibody levels expressed as GMFRs are reported for ancestral, D614G, and B.1.351 variants and RBD binding antibody levels expressed as GMFR for ancestral strain.
Number of Participants Achieving Greater Than or Equal to 4-fold Rise From Before Vaccination in SARS-CoV-2 Full-length Spike and RBD Binding Antibody Levels
Time frame: Day 57 for Cohorts A1 and A2, Day 15 for Cohort B
Data are reported for ancestral, D614G, and B.1.351 variants for Spike binding antibodies and ancestral for RBD binding antibodies.

Results and safety

Results posted to the registry on 15 Oct 2025, as reported by the sponsor. Figures are copied from the record, not re-analysed. Full results on ClinicalTrials.gov.

Participant flow

Group	Started	Completed
Cohort A1: ARCT-021	4	4
Cohort A1: ARCT-165	4	2
Cohort A1: ARCT-154	4	4
Cohort A2: ARCT-021	6	5
Cohort A2: ARCT-154	18	17
Cohort B: ARCT-021	12	9
Cohort B: ARCT-165	12	12
Cohort B: ARCT-154	12	12

Primary outcome: Number of Participants Reporting Solicited Local or Systemic Adverse Events (AEs)

Time frame: Up to Day 8 (7 days after first vaccine administration for Cohorts A1, A2 and B), and up to Day 36 (7 days after second vaccine administration for Cohorts A1 and A2). Count of participants. Unit: Participants

Measure	Cohort A1: ARCT-021 n = 4	Cohort A1: ARCT-165 n = 4	Cohort A1: ARCT-154 n = 4	Cohort A2: ARCT-021 n = 6	Cohort A2: ARCT-154 n = 18	Cohort B: ARCT-021 n = 12	Cohort B: ARCT-165 n = 12	Cohort B: ARCT-154 n = 12
Any Solicited Local AE After Dose 1	3	4	3	5	10	12	10	10
Any Solicited Local AE After Dose 2	2	2	4	6	10	–	–	–
Any Solicited Systemic AE After Dose 1	3	3	1	5	9	12	9	11
Any Solicited Systemic AE After Dose 2	2	2	3	5	10	–	–	–

Population analysed: Measured in the SS: The SS included all randomized participants who received at least one dose of the study vaccine. Assignment of participants to study vaccine group was based on the study vaccine actually received. Number analyzed for Cohort B arms for AEs after Dose 2 = 0 as participants in this Cohort received only a single dose of treatment.

Primary outcome: Number of Participants Reporting Unsolicited AEs

Time frame: Up to Day 29 (28 days after vaccine administration for Cohort B), and up to Day 57 (up to 28 days after each vaccine administration for Cohorts A1 and A2). Count of participants. Unit: Participants

Measure	Cohort A1: ARCT-021 n = 4	Cohort A1: ARCT-165 n = 4	Cohort A1: ARCT-154 n = 4	Cohort A2: ARCT-021 n = 6	Cohort A2: ARCT-154 n = 18	Cohort B: ARCT-021 n = 12	Cohort B: ARCT-165 n = 12	Cohort B: ARCT-154 n = 12
Value	3	3	2	4	15	9	9	10

Primary outcome: Number of Participants Reporting Medically Attended Adverse Events (MAAEs), AEs Leading to Discontinuation From Study Vaccine/Study Withdrawal, or Serious Adverse Events (SAEs)

Time frame: Through Final Visit (365 days after last study vaccine dose); up to a maximum of approximately 394 days. Count of participants. Unit: Participants

Measure	Cohort A1: ARCT-165 n = 4	Cohort A2: ARCT-021 n = 6	Cohort A2: ARCT-154 n = 18	Cohort B: ARCT-021 n = 12	Cohort B: ARCT-165 n = 12
Any MAAEs	1	1	3	2	1
Any AEs Leading to Discontinuation from Study Vaccine/Study Withdrawal	0	0	0	0	0
Any SAEs	0	1	0	1	0

Primary outcome: Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2) Serum Neutralizing Antibody Levels, Expressed as Geometric Mean Concentration (GMC)

Time frame: Baseline, Days 29, 57, 209, Final Visit (approx. Day 394) for Cohorts A1 and A2; Baseline, Days 15, 29, 91, 181, 271 and Final Visit (approx. Day 366) for Cohort B. Geometric mean (95% Confidence Interval). Unit: IU/mL

Measure	Cohort A1: ARCT-021 n = 4	Cohort A1: ARCT-165 n = 3	Cohort A1: ARCT-154 n = 4	Cohort A2: ARCT-021 n = 6	Cohort A2: ARCT-154 n = 18	Cohort B: ARCT-021 n = 12	Cohort B: ARCT-165 n = 12	Cohort B: ARCT-154 n = 12
Pseudoviral D614G; Baseline	8 (NA to NA)	8 (6 to 11)	12 (4 to 33)	421 (74 to 2383)	455 (202 to 1028)	87 (51 to 148)	94 (29 to 301)	114 (58 to 224)
Pseudoviral D614G; Day 15	–	–	–	–	–	1415 (927 to 2160)	2019 (1179 to 3459)	3474 (1577 to 7656)
Pseudoviral D614G; Day 29	36 (0 to 2715)	9 (2 to 47)	26 (6 to 107)	1966 (592 to 6534)	1949 (1026 to 3701)	1741 (1001 to 3028)	2202 (1170 to 4145)	4200 (2274 to 7757)
Pseudoviral D614G; Day 57	42 (2 to 998)	87 (0 to 1334270362)	70 (11 to 452)	2038 (676 to 6143)	3563 (2083 to 6096)	–	–	–
Pseudoviral D614G; Day 91	–	–	–	–	–	1796 (1067 to 3024)	1697 (840 to 3429)	3427 (2113 to 5558)
Pseudoviral D614G; Day 181	–	–	–	–	–	1072 (450 to 2551)	1534 (552 to 4260)	3041 (1334 to 6932)
Pseudoviral D614G; Day 209	90 (2 to 3976)	–	19 (4 to 85)	1340 (100 to 17882)

Adverse events

Time frame: Through Final Visit (365 days after last study vaccine dose); up to a maximum of approximately 394 days. Other adverse events reported at 0% frequency or more

Group	Serious adverse events	Other adverse events	Deaths
Cohort A1: ARCT-021	0 of 4 (0%)	3 of 4 (75%)	0 of 4
Cohort A1: ARCT-165	0 of 4 (0%)	3 of 4 (75%)	0 of 4
Cohort A1: ARCT-154	0 of 4 (0%)	2 of 4 (50%)	0 of 4
Cohort A2: ARCT-021	1 of 6 (16.7%)	4 of 6 (66.7%)	0 of 6
Cohort A2: ARCT-154	0 of 18 (0%)	15 of 18 (83.3%)	0 of 18
Cohort B: ARCT-021	1 of 12 (8.3%)	9 of 12 (75%)	0 of 12
Cohort B: ARCT-165	0 of 12 (0%)	9 of 12 (75%)	0 of 12
Cohort B: ARCT-154	0 of 12 (0%)	10 of 12 (83.3%)	0 of 12

Loading the posted results from ClinicalTrials.gov…

Research links

Official record on ClinicalTrials.govLast updated by the sponsor 15 Oct 2025.
Posted resultsParticipant flow, baseline, all outcome measures and adverse events.
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 3 countries: see every site and its status.

Questions about this trial

What is this clinical trial studying?

A Phase 1/2 study testing ARCT-165, ARCT-154 and ARCT-021 in people with COVID-19 and SARS-CoV-2 Infection, run by Arcturus Therapeutics, Inc. at 4 sites in 3 countries.

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 7 inclusion and 24 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 15 Oct 2025. 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, Singapore, South Africa. 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 15 Oct 2025). 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 Reporting Solicited Local or Systemic Adverse Events (AEs) (time frame: Up to Day 8 (7 days after first vaccine administration for Cohorts A1, A2 and B), and up to Day 36 (7 days after second vaccine administration for Cohorts A1 and A2)). The study lists 14 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 NCT05037097.

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 15 Oct 2025; AzTrials last refreshed its copy on 26 Oct 2026.