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.
Subjects will be recruited and divided into 3 groups:~Experimental Group (384 subjects): 1st dose : combined vaccination of COVAX+IIV4, 2nd dose: combined vaccination of COVAX+PPV23; Control Group A (384 subjects): 1st dose: COVAX only, 2nd dose: COVAX only; Control Group B (384 subjects): 1st dose: IIV4 only, 2nd dose: PPV23 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.