A PhaseⅡ Study to Evaluate the Safety & Immunogenicity of SARS-CoV-2 Alpha/Beta/Delta/Omicron Variants COVID-19 Vaccine

Inclusion Criteria: * The age when signing ICF should meet the requirements of the scheme (Group A ≥18 years old; Group B 12-17 years old; Group C, 3-11 years old) male or female; * Have previously received the recommended dose and immunization procedures of COVID-19 vaccine approved for domestic market, and the interval between signing ICF and receiving the last dose of COVID-19 vaccine is 6-24 months; * Subject and/or guardian or client of both parties are able to sign a written ICF and voluntarily participate in the trial, fully understand the trial procedure, the risks of participating in the trial and the alternative interventions available to non-participants; * The subject and/or the guardian or client of both parties can read, understand and fill in the diary card; * Healthy subjects or subjects with stable underlying diseases. Stable underlying diseases were defined as those who were in stable condition at least 3 months before inclusion in the study, had no significant change in treatment regimen and had not been admitted to hospital due to disease progression; * Fertile men and women of childbearing age voluntarily agree to take effective contraceptive measures from signing the ICF to 180 days after receiving the trial vaccine; Pregnancy tests for women of childbearing age during the screening period were negative. Exclusion Criteria: * Fever (\> 14 years of age, axillary temperature ≥37.3℃; ≤14 years old, axillary temperature ≥37.5℃); * SARS-CoV-2 nucleic acid …