Evaluation of Immunogenicity and Safety of Combined Immunization of COVID-19 Vaccine (Produced in Beijing) and PPV23 / IIV4

This randomized, parallel, controlled study is designed to evaluate the immunogenicity and safety of simultaneously immunization of COVAX + PPV23 and COVAX + IIV4. 1152 subjects are divided into 3 groups, including 1 experimental group and 2 control groups (control group A and B). Each group includes 384 subjects respectively. Experimental Group (384 subjects) will receive: 1st dose : combined vaccination of COVAX+IIV4, 2nd dose: combined vaccination of COVAX+PPV23; Control Group A (384 subjects) will receive: 1st dose: COVAX only, 2nd dose: COVAX only; Control Group B (384 subjects) will receive: 1st dose: IIV4 only, 2nd dose: PPV23 only. Specifically, each group will be divided again. Each 384-subject group is divided again into 2 age-based subgroups: (1) 18-59 years old; (2) ≥60 years old. Each subgroup includes 192 subjects respectively. Blood samples will be collected 3 times: (1) before the 1st dose of vaccinatioin; (2) before the 2nd dose of vaccination; (3) 28 days after the 2nd dose of vaccination. To evaluate the immunogenicity, the investigators will detect and compare the neutralizing antibody levels, the seroconversion rates and antibody geometric mean concentrations. The safety of all groups will be monitored as well.