A Study to Assess the Safety, Reactogenicity, and Immunogenicity of SK Japanese Encephalitis Messenger Ribonucleic Acid (mRNA) Vaccines (GBP560) in Healthy Adults

A 2-Stage, Phase I/II, Active-controlled, Randomized, Observer-blinded, Dose-finding Study to Assess the Safety, Reactogenicity, and Immunogenicity of SK Japanese Encephalitis mRNA Vaccines (GBP560) in Healthy Adults (Aged 18 Years and Older)

This is a 2-Stage, Phase I/II Study to Assess the Safety, Reactogenicity, and Immunogenicity of SK Japanese Encephalitis mRNA Vaccines (GBP560) in Healthy Adults (Aged 18 Years and Older)

Study Overview

• Status: Recruiting
• Conditions: Japanese Encephalitis Virus Disease
• Intervention / Treatment: Biological: GBP560-A; Biological: GBP560-B; Biological: IXIARO; Biological: IMOJEV; Biological: Normal Saline (Placebo)

Detailed Description

The purpose of this study is to assess the safety, reactogenicity and immunogenicity of SK Japanese Encephalitis mRNA vaccines (GBP560) in healthy adults.

• Study Type: Interventional
• Enrollment (Estimated): 402
• Phase: Phase 2; Phase 1

Contacts and Locations

• Study Contact: Name: Sejun Oh; Phone Number: 82-2-2008-2200; Email: sejunoh@sk.com

Study Locations

• Australia
  • Brisbane, Australia
    • Recruiting
    • Nucleus Network - Brisbane (Q Pharm)
    • Principal Investigator: Michael Wong
    • Contact: Gabrielle Robb; Phone Number: +61-7-3707-2784; Email: g.robb@nucleusnetwork.com.au
  • Melbourne, Australia
    • Recruiting
    • Nucleus Network - Melbourne
    • Principal Investigator: Christina Chang
    • Contact: Gabrielle Robb; Phone Number: +61-7-3707-2784; Email: g.robb@nucleusnetwork.com.au
• New Zealand
  • Central City
    • Christchurch, Central City, New Zealand, 8011
      • Not yet recruiting
      • New Zealand Clinical Research
      • Principal Investigator: Cory Sellwood
      • Contact: Kayla Malate; Phone Number: +64 9 373 3474 ext. 7165; Email: kayla.malate@nzcr.co.nz

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

[Age]

1. For Stage 1, participant must be 18 to 55 years of age inclusive, at the time of signing the informed consent.

   For Stage 2, participant must be 18 years of age and older, at the time of signing the informed consent.

   [Type of Participant and Disease Characteristics]

2. Participants who are healthy as determined by medical evaluation including medical history, vital signs, physical examination, clinical laboratory tests and medical judgement of the investigator.
3. Participants who are willing and able to attend all scheduled visits and comply with all study procedures.

4. Body mass index (BMI) within the range of 18.5-29.9 kg/m2 (inclusive) at screening

   [Sex and Contraceptive/Barrier Requirements]

5. All participants must agree to be heterosexually inactive or agree to consistently use at least one acceptable method of contraception from at least 4 weeks prior to the 1st study vaccination to 12 weeks after the last study vaccination (Visit 9) (See Appendix 10.4 for detailed contraceptive methods).

6. Female participants with a negative urine or serum pregnancy test at screening.

   * Female participants who are surgically sterile (e.g., having undergone a full hysterectomy, bilateral salpingectomy, or bilateral oophorectomy) or postmenopausal with amenorrhea for at least 12 months are not subject to a pregnancy test.

   [Informed Consent]

7. Participants who are capable of giving signed informed consent as described in Appendix 10.1.3 which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in this protocol before initiation of any trial-specific procedures.

Exclusion Criteria:

[Medical Conditions]

1. Any clinically significant respiratory symptoms (e.g., cough, sore throat), febrile illness (tympanic temperature >38°C), or acute illness within 24 hours prior to the 1st study vaccination. Prospective participants with these conditions cannot be included until 24 hours after resolution.
2. History of congenital, hereditary, acquired immunodeficiency, or autoimmune disease.
3. Any positive test results for hepatitis B surface antigen, hepatitis C antibody, or human immunodeficiency virus (HIV) at screening.
4. History of bleeding disorder or thrombocytopenia which is contraindicating intramuscular vaccination in the investigator's opinion.
5. History of hypersensitivity and severe allergic reaction (e.g., anaphylaxis, Guillain-Barre syndrome) to any vaccines or components of the study intervention.
6. History of myocarditis, pericarditis or myopericarditis (including the screening 12-lead ECG results from Stage 1 participants), as assessed by the investigator, indicating probable or possible myocarditis, pericarditis, or myopericarditis, or demonstrating clinically significant abnormalities that could affect participant safety or the interpretation of study findings.
7. History of JEV infection/other flaviviruses infection (e.g., Dengue, West Nile, Zika, St. Louis Encephalitis, Yellow fever).
8. History of malignancy within 1 year prior to the 1st study vaccination (with the exception of malignancy with minimal risk of recurrence at the discretion of the investigator).

9. Significant unstable chronic or acute illness that, in the opinion of the investigator, might pose a health risk to the participant if enrolled, or could interfere with the protocol-specified activities, or interpretation of study results.

   * The AESIs as outlined in Section 8.1.4 should be considered for evaluating the participant

10. Any other conditions which, in the opinion of the investigator, might interfere with the evaluation of the study objectives (e.g., alcohol or drug abuse, neurologic or psychiatric conditions).
11. Female participants who are pregnant or breastfeeding.

12. (Only for Stage 1) Current smoker or a recent smoking history within 12 weeks prior to screening. Occasional smoker who smokes up to 10 cigarettes per month may be allowed to participate at the investigator's discretion.

    [Prior/Concomitant medication]

13. Receipt of JEV vaccination/other flaviviruses vaccination in the past.
14. Receipt of any vaccine within 4 weeks prior to the 1st study vaccination or planned receipt of any vaccine from enrollment through 4 weeks after the last study vaccination (Visit 8), except for inactivated influenza vaccination, which may be received at least 2 weeks prior to the 1st study vaccination.
15. Receipt of immunoglobulins and/or any blood or blood-derived products within 12 weeks prior to the 1st study vaccination.

16. Receipt of immunosuppressive therapy, such as any use of anti-cancer chemotherapy or radiation therapy; or systemic corticosteroid therapy (≥10 mg prednisone/day or equivalent) within 12 weeks prior to the 1st study vaccination. The use of inhaled, topical, or nasal glucocorticoid will be permitted.

    [Prior/Concurrent Clinical Study Experience]

17. Participation in another clinical study and receipt of study intervention within 4 weeks prior to the 1st study vaccination, or concurrent, planned participation in another clinical study with study intervention during this study period.

    [Other Exclusions]

18. Investigators, or study staff who are directly involved in the conduct of this study or supervised by the investigator, and their respective family members.
19. Donation of ≥ 450mL (milliliter) of blood product within 4 weeks prior to screening, or planned donation of blood product from enrollment through 12 weeks after the last study vaccination (Visit 9).

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Prevention
• Allocation: Randomized
• Interventional Model: Sequential Assignment
• Masking: Quadruple

Number of Arms

10

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Test group 1-1 (GBP560-A); Low dose level(3µg) for GBP560-A in stage 1. Participants will receive 2 doses of one of the test vaccines at 4-week intervals, respectively.	Biological: GBP560-A; injection volume of 0.5mililiter (mL) with each dose on V2(1day) and V5 (29day) in stage1 and stage2. Low dose: 3μg Mid dose: 15μg High dose: 50μg
Experimental: Test group 1-2 (GBP560-B); Low dose level (3µg) for GBP560-B in stage 1. Participants will receive 2 doses of one of the test vaccines at 4-week intervals, respectively.	Biological: GBP560-B; injection volume of 0.5mL with each dose on V2(1day) and V5 (29day) in stage1 and stage2. Low dose: 3μg Mid dose: 15μg High dose: 50μg
Experimental: Test group1-3 (GBP560-A); Mid dose level (15µg) for GBP560-A in stage 1. Participants will receive 2 doses of one of the test vaccines at 4-week intervals, respectively.	Biological: GBP560-A; injection volume of 0.5mililiter (mL) with each dose on V2(1day) and V5 (29day) in stage1 and stage2. Low dose: 3μg Mid dose: 15μg High dose: 50μg
Experimental: Test group1-4 (GBP560-B); Mid dose level (15µg) for GBP560-B in stage 1. Participants will receive 2 doses of one of the test vaccines at 4-week intervals, respectively.	Biological: GBP560-B; injection volume of 0.5mL with each dose on V2(1day) and V5 (29day) in stage1 and stage2. Low dose: 3μg Mid dose: 15μg High dose: 50μg
Experimental: Test group1-5 (GBP560-A); High dose level (50µg) for GBP560-A in stage 1. Participants will receive 2 doses of one of the test vaccines at 4-week intervals, respectively.	Biological: GBP560-A; injection volume of 0.5mililiter (mL) with each dose on V2(1day) and V5 (29day) in stage1 and stage2. Low dose: 3μg Mid dose: 15μg High dose: 50μg
Experimental: Test group1-6 (GBP560-B); High dose level (50µg) for GBP560-B in stage 1. Participants will receive 2 doses of one of the test vaccines at 4-week intervals, respectively.	Biological: GBP560-B; injection volume of 0.5mL with each dose on V2(1day) and V5 (29day) in stage1 and stage2. Low dose: 3μg Mid dose: 15μg High dose: 50μg
Active Comparator: Control group1 (IXIARO®); Participants will receive 2 doses of one of the active comparators (IXIARO®, 6 Antigen Unit, corresponding to a potency of ≤ 460 ng ED) at 4-week intervals, respectively in Stage 1 and Stage 2.	Biological: IXIARO; injection volume of 0.5mL on V2(1day) and V5 (29day) in stage1 and stage2
Active Comparator: Control group2 (IMOJEV®); Participants will receive 1 dose of placebo saline and 1 dose of another active comparator (IMOJEV®, 4.0 - 5.8 log PFU) at 4-week intervals, respectively in Stage 1 and Stage 2.	Biological: IMOJEV; injection volume of 0.5mL on V5 (29day) in stage1 and stage2; Biological: Normal Saline (Placebo); injection volume of 0.5mL on V2 (1day) in stage1 and stage2 (This is for IMOJEV placebo)
Experimental: Test group 2-1 (GBP560-A or B); Participants will receive 2 intramuscular injections of the test vaccines in stage 2. 1st will be on Visit 2 and 2nd will be on Visit 5, in line with the selected dose regimen in stage 1.	Biological: GBP560-A; injection volume of 0.5mililiter (mL) with each dose on V2(1day) and V5 (29day) in stage1 and stage2. Low dose: 3μg Mid dose: 15μg High dose: 50μg; Biological: GBP560-B; injection volume of 0.5mL with each dose on V2(1day) and V5 (29day) in stage1 and stage2. Low dose: 3μg Mid dose: 15μg High dose: 50μg
Experimental: Test group 2-2 (GBP560-A or B); Participants will receive 2 intramuscular injections of the test vaccines in stage 2. 1st will be on Visit 2 and 2nd will be on Visit 5, in line with the selected dose regimen in stage 1.	Biological: GBP560-A; injection volume of 0.5mililiter (mL) with each dose on V2(1day) and V5 (29day) in stage1 and stage2. Low dose: 3μg Mid dose: 15μg High dose: 50μg; Biological: GBP560-B; injection volume of 0.5mL with each dose on V2(1day) and V5 (29day) in stage1 and stage2. Low dose: 3μg Mid dose: 15μg High dose: 50μg

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Percentage of participants experiencing any immediate reactions	For all cohort	30 minutes (2 hours for the sentinel participants in stage 1) post each vaccination
Percentage of participants reporting any solicited local Adverse Event (AE)	For all cohort	during the 7 days following each study vaccination
Percentage of participants reporting any solicited systemic Adverse Event (AE)	For all cohort	during the 7 days following each study vaccination
Percentage of participants experiencing any unsolicited Adverse Event (AE)	For all cohort	during the 28 days following each study vaccination
Percentage of participants with any Medically Attended Adverse Event (MAAE)	For all cohort	until 6 months following the last study vaccination
Percentage of participants experiencing any Adverse Event of Special Interest (AESI)s, AEs leading to study withdrawal and Serious Adverse Event (SAE)s during the entire study period	For all cohort	up to 12 months for stage 1 and up to 24 months for stage 2
Seroprotection rate for both the respective and cross Japanese encephalitis virus (JEV) strains of each vaccine (SA14-14-2 and Beijing-1 strain) in live-virus neutralizing antibody titers at each time point	For stage 2	At baseline, 2 weeks, 4 weeks following the 1st study vaccination, and at 2 weeks, 4 weeks, 3 months, 6 months, 12 months, and 24 months following the 2nd study vaccination.
Seroresponse rate for both the respective and cross JEV strains of each vaccine (SA14-14-2 and Beijing-1 strain) in live-virus neutralizing antibody titers, from baseline to each subsequent time point	For Stage 2	At baseline, 2 weeks, 4 weeks following the 1st study vaccination, and at 2 weeks, 4 weeks, 3 months, 6 months, 12 months, and 24 months following the 2nd study vaccination
Geometric Mean Titer (GMT) of neutralizing antibody against both the respective and cross JEV strains of each vaccine (SA14-14-2 and Beijing-1 strain) measured by a live-virus neutralization assay (PRNT) at each time point	For stage 2	At baseline, 2 weeks, 4 weeks following the 1st study vaccination, and at 2 weeks, 4 weeks, 3 months, 6 months, 12 months, and 24 months following the 2nd study vaccination.
Geometric mean fold rise of neutralizing antibody against both the respective and cross JEV strains of each vaccine (SA14-14-2,Beijing-1 strain), measured by a live-virus neutralization assay(PRNT), from each pre-vaccination to each subsequent timepoint	For Stage 2	At baseline, 2 weeks, 4 weeks following the 1st study vaccination, and at 2 weeks, 4 weeks, 3 months, 6 months, 12 months, and 24 months following the 2nd study vaccination
Geometric mean fold reduction of neutralizing antibody against both respective and cross JEV strains of each vaccine (SA-14-14-2,Beijing-1 strain), measured by live-virus neutralization assay (PRNT) from persistence baseline to each subsequent timepoint	For Stage 2	At baseline, 2 weeks, 4 weeks following the 1st study vaccination, and at 2 weeks, 4 weeks, 3 months, 6 months, 12 months, and 24 months following the 2nd study vaccination.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Seroprotection rate for both the respective and cross JEV strains of each vaccine (SA14-14-2 and Beijing-1 strain) in live-virus neutralizing antibody titers at each time point	For Stage 1	At baseline, 2 weeks, 4 weeks following the 1st study vaccination, and at 2 weeks, 4 weeks, 3 months, 6 months, and 12 months following the 2nd study vaccination
Seroresponse rate for both the respective and cross JEV strains of each vaccine (SA14-14-2 and Beijing-1 strain) in live-virus neutralizing antibody titers, from baseline to each subsequent time point.	For stage 1	At baseline, 2 weeks, 4 weeks following the 1st study vaccination, and at 2 weeks, 4 weeks, 3 months, 6 months, and 12 months following the 2nd study vaccination
GMT of neutralizing antibody against both the respective and cross JEV strains of each vaccine (SA14-14-2 and Beijing-1 strain) measured by a live-virus neutralization assay (PRNT) at each time point	For stage 1	At baseline, 2 weeks, 4 weeks following the 1st study vaccination, and at 2 weeks, 4 weeks, 3 months, 6 months, and 12 months following the 2nd study vaccination
Geometric mean fold rise of neutralizing antibody against both the respective and cross JEV strains of each vaccine (SA14-14-2,Beijing-1 strain), measured by live-virus neutralization assay(PRNT), from each pre-vaccination to each subsequent timepoint	For stage 1	At baseline, 2 weeks, 4 weeks following the 1st study vaccination, and at 2 weeks, 4 weeks, 3 months, 6 months, and 12 months following the 2nd study vaccination.
Geometric mean fold reduction of neutralizing antibody against both respective and cross JEV strains of each vaccine (SA-14-14-2,Beijing-1 strain),measured by live-virus neutralization assay(PRNT) from persistence baseline to each subsequent timepoint	For Stage1	At baseline, 2 weeks, 4 weeks following the 1st study vaccination, and at 2 weeks, 4 weeks, 3 months, 6 months, and 12 months following the 2nd study vaccination.
Cell-mediated response for cytokines expressed by Cluster of Differentiation 4+ Cluster of Differentiation 8+ T cells (Interferon-γ, Tumor Necrosis Factor-α, measured by Fluorescence-Activated Cell Sorting-Intracellular Cytokine Staining assay.	For all cohort	At baseline, 4 weeks following the 1st study vaccination, and at 4 weeks and 6 months following the 2nd study vaccination

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Seroprotection rate for the heterologous JEV strains of each vaccine (including, but not limited to K95A07, Bennett, JKT 6468, Sangju-v1 strains) in live-virus neutralizing antibody titers at each timepoint.	will be evaluated exclusively in a subset of approximately 20% of participants in stage 1, 10% of participants in stage 2	At baseline, 2 weeks, 4 weeks following the 1st study vaccination, and at 2 weeks, 4 weeks, 3 months, 6 months, and 12 months following the 2nd study vaccination. and 24 months following the 2nd study vaccination (for stage2 only)
GMT of neutralizing antibody against the heterologous JEV strains of each vaccine (including, but not limited to K95A07, Bennett, JKT 6468, Sangju-v1 strains) measured by a live-virus neutralization assay (PRNT) at each timepoint	will be evaluated exclusively in a subset of approximately 20% of participants in stage 1, 10% of participants in stage 2	At baseline, 2 weeks, 4 weeks following the 1st study vaccination, and at 2 weeks, 4 weeks, 3 months, 6 months, and 12 months following the 2nd study vaccination. and 24 months following the 2nd study vaccination (for stage2 only)
Seroresponse rate for the heterologous JEV strains of each vaccine (including, but not limited to K95A07, Bennett, JKT 6468, Sangju-v1 strains) in live-virus neutralizing antibody titers, from baseline to each subsequent time point	will be evaluated exclusively in a subset of approximately 20% of participants in stage 1, 10% of participants in stage 2	At baseline, 2 weeks, 4 weeks following the 1st study vaccination, and at 2 weeks, 4 weeks, 3 months, 6 months, and 12 months following the 2nd study vaccination. and 24 months following the 2nd study vaccination (for stage2 only)
Geometric mean fold rise of neutralizing antibody against the heterologous JEV strains of each vaccine (including,but not limited to K95A07, Bennett, JKT 6468, Sangju-v1) measured by the PRNT assay, from each pre-vaccination to each subsequent time point	will be evaluated exclusively in a subset of approximately 20% of participants in stage 1, 10% of participants in stage 2.	At baseline, 2 weeks, 4 weeks following the 1st study vaccination, and at 2 weeks, 4 weeks, 3 months, 6 months, and 12 months following the 2nd study vaccination. and 24 months following the 2nd study vaccination (for stage2 only)

Collaborators and Investigators

• Sponsor: SK Bioscience Co., Ltd.

Study record dates

Study Major Dates

• Study Start (Actual): February 24, 2025
• Primary Completion (Estimated): June 26, 2026
• Study Completion (Estimated): March 19, 2028

Study Registration Dates

• First Submitted: October 28, 2024
• First Submitted That Met QC Criteria: November 6, 2024
• First Posted (Actual): November 8, 2024

Study Record Updates

• Last Update Posted (Actual): December 23, 2025
• Last Update Submitted That Met QC Criteria: December 16, 2025
• Last Verified: December 1, 2025

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Infectious Encephalitis; Vector Borne Diseases; Neuroinflammatory Diseases; Mosquito-Borne Diseases; Brain Diseases; Central Nervous System Diseases; Nervous System Diseases; Infections; RNA Virus Infections; Virus Diseases; Arbovirus Infections; Flavivirus Infections; Flaviviridae Infections; Encephalitis, Viral; Central Nervous System Viral Diseases; Central Nervous System Infections; Encephalitis; Encephalitis, Arbovirus; Encephalitis, Japanese; Pharmaceutical Preparations; Crystalloid Solutions; Isotonic Solutions; Solutions; Saline Solution
• Other Study ID Numbers: GBP560_001

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No