This study is a single-center, randomized, double-blind, active-controlled Phase Ⅲ clinical trial, as well as an immuno-bridging clinical trial by parallel testing previous serum after primary immunization of COVID-19 vaccine (Vero cell), inactivated (Omicron variant). The main purpose of this study is to evaluate the superiority of immunogenicity against SARS-CoV-2 Omicron strain induced by one-dose booster immunization of inactivated COVID-19 vaccine (Omicron variant)developed by Sinovac Life Sciences Co., Ltd.in subjects who have received two- or three-dose COVID-19 vaccine（CZ strain）, compared with one-dose booster of COVID-19 vaccine（CZ strain）in subjects who have received three-dose COVID-19 vaccine（CZ strain）and to evaluate the non-inferiority of immunogenicity against SARS-CoV-2 Omicron strain induced by one-dose booster immunization of inactivated COVID-19 vaccine (Omicron variant), developed by Sinovac Life Sciences Co., Ltd, in subjects who have received two- or three-dose COVID-19 vaccine（CZ strain）,compared with the immunogenicity against SARS-CoV-2（CZ strain）induced by two-dose COVID-19 vaccine（CZ strain）primary immunization. This clinical trial consists of two stages. A total of 1750 healthy subjects will be enrolled including 1500 healthy subjects aged 18 years and older who have received 2 or 3 doses of the COVID-19 vaccine（CZ strain）（750 population were vaccinated with 2 doses and 3 doses of COVID-19 vaccine（CZ strain）respectively）in stage I of the clinical trial,250 subjects in stage Ⅱ of the clinical trial.~Stage I of the clinical trial:1500 healthy subjects （750 population were vaccinated with 2 doses or 3 doses of COVID-19 vaccine（CZ strain）respectively）who have received two or three doses of the prototype (CZ strain) COVID-19 vaccine, including 1200 subjects aged 18~59 years old and 300 subjects aged 60 years and above. Subjects in each age group will be randomly divided into experimental group and control group in a ratio of 2:1. Subjects in the experimental group will receive one dose of inactivated COVID-19 vaccine (Omicron variant), and subjects in the control group will receive one dose of COVID-19 vaccine（CZ strain）.~Stage Ⅱ of the clinical trial:Backup serum samples will be selected from 250 healthy adult subjects aged 26-45 years who received two doses of inactivated COVID-19 vaccine(CZ strain)from clinical trial of lot-to-lot consistency of an inactivated SARS-CoV-2 Vaccine(Pro-NCOV-4001).
This is a randomized, double-blind, active-controlled Phase Ⅲ clinical trial, as well as an immuno-bridging clinical trial by parallel testing previous serum after primary immunization of COVID-19 vaccine (Vero cell), inactivated (Omicron variant). The main purpose of this study is to evaluate the superiority of immunogenicity against SARS-CoV-2 Omicron strain induced by one-dose booster immunization of inactivated COVID-19 vaccine (Omicron variant), developed by Sinovac Research and Development Co., Ltd.in subjects who have received two- or three-dose Prototype COVID-19 vaccine （CZ strain）, compared with one-dose booster of Prototype COVID-19 vaccine （CZ strain） in subjects who have received three-dose Prototype COVID-19 vaccine （CZ strain）, and to evaluate the non-inferiority of immunogenicity against SARS-CoV-2 Omicron strain induced by one-dose booster immunization of inactivated COVID-19 vaccine (Omicron variant), developed by Sinovac Research and Development Co., Ltd., in subjects who have received two- or three-dose Prototype COVID-19 vaccine, compared with the immunogenicity against SARS-CoV-2 Prototype strain induced by two-dose Prototype COVID-19 vaccine（CZ strain）after primary immunization.