A Randomized, Controlled, Multicenter Phase 4 Clinic Trial to Evaluate the Immunogenicity and Safety of Combined Immunization of Inactivated SARS-CoV-2 Vaccines (Vero Cell) (COVAX) (Produced in Wuhan) and 23-valent Pneumococcal Polysaccharide Vaccine (PPV23) or Quadrivalent Inactivated Influenza Vaccine (IIV4)
Subjects will be recruited and divided into 3 groups: Experimental Group (468 subjects): 1st dose : combined vaccination of COVAX+PPV23, 2nd dose: combined vaccination of COVAX+IIV4; Control Group A (468 subjects): 1st dose: COVAX only, 2nd dose: COVAX only; Control Group B (468 subjects): 1st dose: PPV23 only, 2nd dose: IIV4 only. Blood samples will be collected 3 times: before the 1st dose of vaccinatioin; before the 2nd dose of vaccination; 28 days after the 2nd dose of vaccination. The immunogenicity and safety of both experimental and control groups will be analyzed.