Phase 3, open-label, Russian, multicenter, single-arm trial to evaluate the immunogenicity of varicella vaccine (VARIVAX™) in healthy infants, children, and adolescents.

Varicella (chickenpox) is a common, highly contagious disease caused by primary infection with varicella zoster virus (VZV), which can result in bacterial superinfection, central nervous system complications, and hospitalization. Stage 2 of this Phase 3 open-label study (ClinicalTrials.gov identifier: NCT03843632) enrolled 100 healthy infants, children, and adolescents (12 months-6 years, n = 37; 7-12 years, n = 33; 13-17 years, n = 30) without a clinical history of varicella. Participants aged 12 months-12 years were administered 1 dose of VARIVAX™ 0.5 mL (Varicella Virus Vaccine Live [Oka/Merck]) and adolescents aged 13-17 years were administered 2 doses 6 weeks apart. For participants seronegative at baseline (VZV antibody titer <1.25 glycoprotein enzyme-linked immunosorbent assay [gpELISA] units/mL), immunogenicity was assessed by seroconversion (VZV antibody titer ≥5 gpELISA units/mL) and VZV antibody geometric mean titers 6 weeks after the final dose. For participants who were VZV seropositive at baseline (VZV antibody titer ≥1.25 gpELISA units/mL), immunogenicity was assessed by antibody titer geometric mean fold rise and percentage of participants with ≥4-fold rise in antibody titer 6 weeks after the final dose. A Vaccine Report Card was used to report solicited and unsolicited adverse events through 42 days post-vaccination. After series completion among seronegative participants across age groups (n = 74), 98.6% demonstrated seroconversion 6 weeks post-vaccination; among seropositive participants (n = 26), 65.4% had ≥4-fold rise in antibody titer 6 weeks post-vaccination. No new safety signals were observed. Administering VARIVAX to infants, children, and adolescents resulted in an acceptable immune response with a safety profile consistent with the licensed product.