inclusion criteria: participated in the clinical studies on the safety and immunogenicity of inactivated covid-19 vaccine combined immunization with 23-valent pneumococcal polysaccharide vaccine in rushan city, shandong province from july to october 2021; the interval between complete immunization with two doses of covid-19 vaccine is 6-8 months; subjects will be willing to participate in the study and follow the study procedure to collect venous blood; proven legal identity;

inclusion criteria: participated in the clinical studies on the safety and immunogenicity of inactivated covid-19 vaccine combined immunization with 23-valent pneumococcal polysaccharide vaccine in rushan city, shandong province from july to october 2021; the interval between complete immunization with two doses of covid-19 vaccine is 6-8 months; subjects will be willing to participate in the study and follow the study procedure to collect venous blood; proven legal identity;