GMT of anti-RBD specific antibody at Month 1 after boost vaccination.;Occurrence of adverse events (AE) within 7 days after each dose of the recombinant SARS-CoV-2 vaccine (Sf9 cell) or placebo;

GMT of anti-RBD specific antibody at Month 1 after boost vaccination.;Occurrence of adverse events (AE) within 7 days after each dose of the recombinant SARS-CoV-2 vaccine (Sf9 cell) or placebo;