This is a randomized, double-blinded, and positive-controlled phaseⅡb clinical trial of 640 participants aged 18 years and above, who have completed 2 doses of inactivated COVID-19 vaccine (CoronaVac®) or mRNA COVID-19 vaccine (Comirnaty) as the primary vaccination. Participants will be enrolled and randomly assigned into two arms at a ratio of 1:1 to receive a booster dose of medium-dose (600SU) or high-dose (1200SU) COVID-19 Vaccine. For those who were vaccinated with CoronaVac®, the booster dose will be given 3-8 months after their second dose. For those who were vaccinated with Comirnaty, the booster dose will be given 6-8 months after their second dose. Each participant will be collected 5.0 ml blood sample before vaccination and 14 days,3 months and 6 months after booster immunization.Immunogenicity assessments will be determined by neutralizing antibodies in all participants.In addition,all participants will be monitored for immediate reactions (within 30 minutes) after the booster dose vaccination, adverse events of special interest (AESIs) and serious adverse events (SAEs) for 12 months after booster dose inoculation. In addition, all participants in will be monitored for local and systemic solicited adverse events (AEs) within 7 days and the unsolicited AEs within 28 days.
This is a randomized, double-blinded, and positive-controlled Phase IIb clinical trial of COVID-19 vaccine (CoronaVac®) manufactured by Sinovac Research & Development Co., Ltd.The purpose of this study is to evaluate the immunogenicity of using the high (1200SU) or medium (600SU) dose of CoronaVac® as the booster dose.