Second dose of chickenpox (varicella) vaccine for healthy children

Immunogenicity and Safety of the Second Dose of Varicella Vaccine in Healthy Children: An Open-label Study

This project will give a Sinovac second dose of the chickenpox vaccine to children aged 15 months–12 years who had a first dose at 12 months to see if switching brands is safe and produces good immune responses.

Quick facts

• Phase: Phase 3
• Study type: Interventional
• Enrollment: 300 (estimated)
• Ages: 15 Months to 12 Years
• Sex: All
• Sponsor: Sinovac (Dalian) Vaccine Technology Co., Ltd. (Industry-sponsored)
• Drugs / interventions: prednisone
• Locations: 5 sites (Akdeniz and 4 other locations)
• Trial ID: NCT07475000 on ClinicalTrials.gov

What this trial studies

This Phase 3 trial will enroll about 300 healthy children in Turkey who received a first varicella dose at 12 months and assign them to five groups based on the brand of their initial vaccine. All participants will receive the second dose manufactured by Sinovac and will be followed for up to 42 days to record safety events and immune responses. Blood samples will be collected before and after vaccination to measure antibody responses and document immunogenicity. Written parental consent and age-appropriate assent will be obtained prior to enrollment.

Who should consider this trial

Good fit: Healthy children aged 15 months to 12 years who received one varicella vaccine dose at 12 months in Turkey and whose parents or legal guardians can provide consent and attend study visits.

Not a fit: Children with prior reported chickenpox infection, recent exposure to varicella, those who have already received more than one varicella dose, or those with a known severe allergy to vaccine components are unlikely to benefit from this protocol.

Why it matters

Potential benefit: If successful, the results could support safely giving a Sinovac second dose after different first-dose brands, simplifying vaccination schedules and improving protection against chickenpox.

How similar studies have performed: Two-dose varicella schedules are known to produce stronger immunity than a single dose, but evidence specifically about switching brands for the second dose is more limited.

Eligibility criteria

Inclusion Criteria:

1. Healthy children aged 15 months to 12 years.
2. Have received one dose of varicella vaccine at 12 months of age in Turkey (verified by vaccination card or official electronic immunization record).
3. Written informed consent obtained from parent(s) or legally authorized representative(s); assent obtained from children as applicable according to local regulations.
4. Able to comply with study procedures, as assessed by the investigator.
5. Able to provide verifiable identification and be contacted for study follow-up during the study period.

Exclusion Criteria:

1. History of varicella-zoster virus (VZV) infection (based on parental report or medical record).
2. Known exposure to VZV within 4 weeks prior to screening.
3. Receipt of more than one dose of varicella vaccine.
4. Interval between first dose of varicella vaccine and enrollment less than 3 months.
5. Known allergy to any vaccine component or history of severe allergic reaction to any vaccine (e.g., urticaria, dyspnea, angioedema).
6. Known or suspected immunodeficiency or autoimmune disease (including but not limited to systemic lupus erythematosus, ankylosing spondylitis, autoimmune thyroid disease, asplenia, functional asplenia, or HIV infection).
7. Poorly controlled chronic disease or history of severe systemic disease.
8. Current or history of severe neurological disorders (e.g., epilepsy, convulsions or seizures excluding simple febrile seizures) or psychiatric disorders.
9. Receipt of ≥14 days of immunosuppressive or immunomodulatory therapy (e.g., prednisone ≥20 mg/day or ≥2 mg/kg/day or equivalent), or cytotoxic therapy within 180 days prior to screening, or planned use during the study period.
10. Receipt of blood products or immunoglobulins within 180 days prior to screening, or planned receipt during the study period.
11. Receipt of other investigational drugs or vaccines within 30 days prior to screening, or planned receipt during the study period.
12. Receipt of live attenuated or nucleic acid vaccines within 28 days prior to screening, or subunit or inactivated vaccines within 7 days prior to screening.
13. Fever (axillary temperature \>37.2°C), abnormal vital signs, or clinically significant abnormal findings on physical examination on the day of vaccination.
14. Skin conditions at the intended injection site (e.g., inflammation, ulceration, rash, scar, or other conditions that may interfere with administration or safety assessment).
15. Acute illness or exacerbation of chronic disease within 7 days prior to vaccination, or known or suspected active infection.
16. Any condition that, in the opinion of the investigator, would make the participant unsuitable for participation in the study.

Where this trial is running

Akdeniz and 4 other locations

• Akdeniz University Health, Research and Application Center (Hospital), Department of Child Health and Diseases, Department of Social Pediatrics — Akdeniz, Turkey (Türkiye) (Recruiting)
• Ankara Bilkent City Hospital, Pediatrics and Pediatric Infectious Diseases Clinic — Ankara, Turkey (Türkiye) (Not_yet_recruiting)
• Hacettepe University Hospitals, Department of Pediatrics, Department of Social Pediatrics — Ankara, Turkey (Türkiye) (Recruiting)
• REPUBLIC of TURKEY MINISTRY of HEALTH ANKARA BILKENT CITY HOSPITAL — Ankara, Turkey (Türkiye) (Not_yet_recruiting)
• Ege University Hospital (Application and Research Center) Department of Child Health and Diseases — Ege, Turkey (Türkiye) (Not_yet_recruiting)

Conditions Varicella; Varicella Immunisation