Safety and Immunogenicity of Recombinant COVID-19 Variant Vaccine (Sf9 Cell) as a Booster

This is a randomized, phase Ⅱ, single-blind, randomized, parallel-group controlled clinical trial. The study plans to enroll subjects who have completed homologous primary vaccination with either inactivated or mRNA or Viral Vector COVID-19 vaccines (one or two doses) and have not been infected with COVID-19. All subjects will be evaluated for safety and immunogenicity after a single dose booster immunization with Recombinant COVID-19 variant Vaccine (Sf9 Cell) or inactivated COVID-19 vaccine (Vero cell) or mRNA vaccine or Viral Vector vaccine. The study plans to enroll about 600 subjects aged 18 years and above (subjects aged ≥ 60 years account for approximately 10%) that would be divided into three cohorts according to different primary vaccination: Inactivated COVID-19 vaccines cohort, mRNA COVID-19 vaccines cohort and Viral Vector COVID-19 vaccines cohort, with approximately 200 cases in each cohort. The subjects will be randomized to the Recombinant COVID-19 variant Vaccine (Sf9 Cell) group (test group) or the inactivated COVID-19 vaccine (Vero cell) group or mRNA vaccine or Viral Vector vaccine (control group) in a ratio of 1:1.