The goal of this study is to evaluate the safety and immunogenicity of an investigational varicella vaccine in children. Researchers will compare the investigational vaccine, NBP608, with licensed varicella vaccines. The study includes children aged 12 months to 12 years.

Approximately 780 participants will take part in this study. Participants will be randomly assigned to receive either the investigational vaccine (NBP608) or licensed varicella vaccines. Some participants will receive two doses, while others will receive one dose, according to the assigned study group.

Participants will:

Receive two subcutaneous injections of a study vaccine, administered approximately three months apart (if applicable).

Visit the study clinic seven times over approximately 15 months. Receive follow-up phone calls 7 days after each vaccination to monitor for safety.

This is a Phase III, randomized, Double-blinded, Active-controlled, Multinational, Multicenter study designed to evaluate the safety and immunogenicity of a two-dose regimen of NBP608 in children aged 12 months to 12 years.

Approximately 780 participants will be enrolled in this multinational, multicenter, randomized study and assigned in a 4:4:4:1 ratio to four groups: two investigational vaccine groups (NBP608 mid-potency and low-potency) and two active control groups (licensed varicella vaccines, Varivax® and SKYVaricella®). Each of the NBP608 groups and Active Control Group 1 (Varivax®) will include approximately 240 participants, while Active Control Group 2 (SKYVaricella®) will include approximately 60 participants.

Within each group, participants will be further randomized in a 3:1 ratio to receive either two doses or one dose of the assigned study vaccine.

Immunogenicity will be assessed using blood samples collected at predefined time points to evaluate immune responses to varicella. Safety will be evaluated throughout the study by monitoring adverse events (AEs), serious adverse events (SAEs), and adverse events of special interest (AESIs) following vaccination.

Each participant will take part in the study for approximately 15 months, including scheduled clinic visits and follow-up assessments. The overall study duration will depend on enrollment progress and completion of follow-up across all participating countries.

Inclusion Criteria:

Age

1. Participant must be ≥12 months to ≤12 years of age, at the time of informed consent.

   Type of Participant and Disease Characteristics

2. Participant is healthy or medically stable, as determined by the investigator through medical history, physical examination, and overall clinical assessment.

   * Medically stable condition is defined as no significant change in therapy and no hospitalization for worsening disease within 8 weeks prior to the first study vaccination

3. Participant's parents/LARs are able and willing to comply with all study procedures and attend all scheduled visits.

   Sex and Contraceptive/Barrier Requirements

4. Female participants of childbearing potential (i.e., post-menarcheal females) must agree to maintain complete sexual abstinence from heterosexual intercourse, from at least 4 weeks prior to the first study vaccination and through 12 weeks following the second study vaccination (Visit 5).

5. Female participants of a childbearing potential must have a negative urine pregnancy test at screening; pregnancy testing is not required for those not of childbearing potential.

   Informed Consent/Assent

6. Participant's parents/LARs are capable of providing signed informed consent, including agreement to comply with the requirements and restrictions specified in this protocol and in the informed consent form (ICF), before initiation of any study-specific procedures. Where applicable, the participant must also be able to provide written assent in accordance with local regulations and IRB/IEC requirements.

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 any study vaccination (Participant may be enrolled 24 hours after resolution of these symptoms).

2. History of suspected or laboratory-confirmed VZV infection

3. Close contact or household exposure to an individual with suspected or laboratory-confirmed VZV infection within 4 weeks prior to the first study vaccination.

4. Household member(s) considered at high risk of severe VZV infection, including:

   • Immunocompromised individuals
   • Pregnant women or newborn infants whose mothers lack history of varicella infection or varicella vaccination
   • Newborn infants born at < 28 weeks gestational age.

5. History of congenital, hereditary, acquired immunodeficiency, or autoimmune disease.

6. History of bleeding disorder or thrombocytopenia contraindicating subcutaneous vaccination, based on the investigator's judgment.

7. History of hypersensitivity and severe allergic reaction (e.g., anaphylaxis) to any vaccines or to any components of the study intervention, including gelatin or neomycin.

8. History of Guillain-Barre syndrome following receipt of any prior vaccines.

9. Active untreated tuberculosis infection.

10. Significant unstable chronic or acute illness that, in the investigator's judgment, could pose a risk to the participant's safety, interfere with protocol-specified procedures, or complicate the interpretation of study results.

11. Any other medical conditions that, in the opinion of the investigator, might interfere with the evaluation of study objectives (e.g., major congenital anomalies, neurological disorders, history of seizure disorders)

    Prior/Concomitant therapy

12. Prior receipt of any varicella-containing vaccine.

13. Receipt of any vaccine within 4 weeks prior to the first study vaccination, except influenza vaccine, which may be received ≥ 2 weeks prior, and pneumococcal conjugate vaccine (PCV), for which the last dose of the primary series must have been administered ≥ 8 weeks prior to the first study vaccination.

14. Receipt of any live-attenuated vaccine within 4 weeks prior to the first study vaccination, or planned receipt of any live-attenuated vaccine through 4 weeks following each study vaccination, if not administered on the same day as the study vaccine.

15. Receipt of antiviral medications within 4 weeks prior to the first study vaccination, or planned use of antiviral medications at any time during the study through 6 weeks following the second vaccination.

16. Receipt of salicylates within 2 weeks prior to the first study vaccination, or planned use of salicylates at any time during the study through 6 weeks following the second vaccination.

17. Receipt of immunoglobulins (except for BeyfortusTM [nirsevimab]) or any blood products within 24 weeks prior to the first study vaccination, or planned receipt at any time during the study period.

18. Receipt or planned chronic use (defined as > 2 consecutive weeks) of systemic immunosuppressive therapy or immune-modifying medications, including anti-cancer chemotherapy, radiation therapy; or systemic corticosteroids (equivalent to ≥ 1 mg/kg/day of prednisone or 20 mg/day for individuals weighing >10 kg) within 24 weeks prior to the first study vaccination throughout the end of the study period (Use of inhaled, topical, or intranasal glucocorticoids is permitted).

    Prior/Concurrent Clinical Study Experience

19. Participation in another clinical study involving study intervention within 4 weeks (6 months in Korea in accordance with local regulations) prior to the first study vaccination, or concurrent / planned participation in another clinical study involving study intervention during this study.

    Other Exclusions

20. Investigators, study staff directly involved in conducting the study or supervised by the investigator, and their respective family members.