Safety and Immunogenicity Study of Booster Vaccination With Medium-dosage or High-dosage SARS-CoV-2 Inactivated Vaccine for Prevention of COVID-19

This study a randomized, double-blinded, phase ⅠV clinical trial of SARS-CoV-2 inactivated vaccine .The purpose of this study is to evaluate the safety and immunogenicity of booster vaccination with high-dosage SARS-CoV-2 vaccine in populations who have received two-dose Coronavac with 2nd dose vaccinated more than 6 month.A total of 1200 subjects who have received two-dose Coronavac with 2nd dose vaccinated more than 6 month will be enrolled.All of subjects will be randomly divided into two groups in a 1:1 ratio .Subjects in experimental group will receive high-dosage SARS-CoV-2 inactivated vaccine.Subjects in control group will receive medium-dosage SARS-CoV-2 inactivated vaccine .