Immunogenicity and safety of a live attenuated varicella vaccine in children 1-12 years of age: A randomized, blinded, controlled, non-inferiority phase 3 clinical trial

Objectives: To evaluate the immunogenicity and safety of a live attenuated varicella vaccine produced using a cell factory process. Methods: In this randomized, blinded, controlled, non-inferiority phase 3 clinical trial conducted in Guizhou, healthy children aged 1-12 years were randomly assigned in a 2: 1 ratio to receive one dose of experimental or control vaccine. Physical examination and first blood collection were performed preimmunization on day 0. Diary cards were collected after day 15. Contact cards and second blood samples were collected on day 30. The primary immunogenicity endpoint was the positive conversion rate of the anti-varicella virus antibody at 30 days postimmunization in susceptible children. Secondary endpoints were the fourfold increase rate, positive conversion rate, geometric mean titer, and geometric mean increase at 30 days after immunization in the total cohort. Results: Of the 900 children assessed for eligibility, 894 received an experimental or control vaccine. Both the full analysis and safety analysis sets included 894 subjects. The seroconversion rate in the susceptible population was 95.84% in the experimental and 94.76% in the control group. The lower limit of the 95% confidence interval difference was -2.37%, which was greater than the non-inferiority margin set by the program (-10%). No significant difference in solicited adverse reactions was found between the groups. Within 6 months postimmunization, a total of 24 serious adverse events were reported, none related to the studied vaccine. Conclusion: The live attenuated varicella vaccine produced using a cell factory process was highly immunogenic, safe, and non-inferior to the product in the market. Further studies need to be implemented in the immune persistence, the epidemiological effectiveness and the rare adverse reactions.