Study on Heterologous Prime-boost of Recombinant COVID-19 Vaccine (Ad5 Vector) and RBD-based Protein Subunit Vaccine

This is a randomized, observer-blind, placebo-controlled study, for evaluation of safety and immunogenicity of heterologous prime-boost immunization of recombinant COVID-19 vaccine (adenovirus type-5 vector) and RBD-based protein subunit vaccine (ZF2001) against COVID-19 in Chinese healthy population. 120 healthy subjects aged over 18 years of age who have been vaccinated with recombinant adenovirus type-5 vectored vaccine will be recruited in this study. Of them, 60 subjects will be enrolled in the "0-28 days" regimen and other 60 will be enrolled in "0-56 days" regimen. Subjects, 30 of them are 18-59 years old and 30 are 60 years old and above in each regimen will be randomly vaccinated with the second dose of subunit vaccine(ZF2001) against COVID-19 or a commercial influenza vaccine in a ratio of 2:1. They will then be vaccinated with the third dose of ZF2001 on month 4 after the second dose. The occurrence of adverse events within 28 days and serious adverse events within 6 months after the last vaccination will be observed. In addition, blood samples will be collected on day 0 before the second vaccination, day 14, 28 after the second vaccination and day 14, month 6 after third vaccination to test serum antibody levels and to profile the immune cells' subgroups and germlines. Each subject will remain in this study for approximately 12 months.