Immunogenicity and Safety of a Live Attenuated Varicella Vaccine in Healthy Children Aged 12 to 15 Months: A Phase III, Randomized, Double-Blind, Active-Controlled Clinical Trial.

Objectives

The varicella vaccine (VarV) produced by Sinovac (Dalian) obtained World Health Organization (WHO) prequalification in November 2022. However, no direct comparative studies have been conducted between VarV and other WHO-prequalified varicella vaccines. The study aimed to assess the immunogenicity and safety of Sinovac's VarV compared with Merck Sharp & Dohme's (MSD) VARIVAX® (Moorgate, London, UK) following a single dose administration.

Methods

This Phase III, randomized, double-blind, active-controlled, non-inferiority trial was conducted in the Philippines. Healthy children aged 12 to 15 months were enrolled. Eligible participants were randomly assigned (1:1) to receive a single dose of varicella vaccine either manufactured by Sinovac (Test group) or MSD (Active control group). Immunogenicity was evaluated 6 weeks after vaccination by enzyme-linked immunosorbent assay (ELISA). The primary immunogenicity endpoint was seroresponse rate 6 weeks after vaccination. Seroresponse rate was defined as varicella-zoster virus (VZV) antibody concentration ≥ 10 mIU/mL in participants who were seronegative (antibody concentration < 10 mIU/mL) at baseline. The secondary endpoint was the corresponding geometric mean concentration (GMC). Adverse events (AEs) and serious adverse events (SAEs) were monitored for 6 weeks after vaccination.

Results

Among the 484 participants analyzed, the seroresponse rates 6 weeks after vaccination were 98.85% and 98.88% in the Test group and Active control group, respectively, with a difference of -0.03% (95% CI: -3.10%, 2.99%), which exceeded the predefined non-inferiority margin of -10%. The corresponding GMCs were 35.73 mIU/mL and 37.34 mIU/mL, respectively, with the ratio of 0.96 (95% CI: 0.86, 1.06), also exceeding the predefined non-inferiority margin of 0.67. Furthermore, the incidence of adverse reactions (ARs) in the Test group was lower than that in the Active control group (38.08% vs. 55.51%).

Conclusions

Sinovac's VarV demonstrated non-inferior immunogenicity to WHO-prequalified comparator vaccine (VARIVAX®) and favorable safety profile. These findings indicated that VarV (Sinovac, Beijing, China) met WHO standards for varicella vaccine evaluation, supporting its global use consideration.