Booster Study of COVID-19 Protein Subunit Recombinant Vaccine

This trial is observer-blind, randomized, prospective intervention study. In this study 900 subjects who had received complete primary doses of authorized/approved inactivated (Sinovac®), mRNA (Pfizer®), or viral vector (AstraZeneca®) COVID-19 vaccine and willing to participate in the booster study by signing the consent form, will be involved in this trial. Subject will be divided into six groups, each 150 subjects per arm who had received a complete primary dose of inactivated (Sinovac®) vaccine, mRNA (Pfizer®) vaccine, or viral vector (AstraZeneca®) vaccine will receive one booster dose of SARS-CoV-2 subunit protein recombinant vaccine or active control.