This is a phase Ⅳ follow-up clinical trial based on the previous Phase Ⅳ clinical trial of an inactivated COVID-19 vaccine (CoronaVac) manufactured by Sinovac Life Sciences Co., Ltd.The purpose of this study is to evaluate the immunogenicity,safety and cross-immune response of booster immunization using COVID-19 vaccine,to compare the similarities and differences of immune responses between primary immunization and booster immunization and to detect antibody against hepatitis A and evaluate the immune persistence of the one dose immunization schedule of hepatitis A vaccine in healthy population aged 18 years and older.

This study is a phase 4 clinical trial to evaluate the immunogenicity,safety and cross-immune response of booster immunization using COVID-19 vaccine，to compare the similarities and differences of immune responses between primary immunization and booster immunization and to detect antibody against hepatitis A and evaluate the immune persistence of the one dose immunization schedule of hepatitis A vaccine in healthy population aged 18 years and older. The experimental vaccine is manufactured by Sinovac Life Sciences Co., Ltd.. A total of 180 healthy subjects received two dose of inactivated COVID-19 vaccine (CoronaVac) based on primary immunization in previous Phase Ⅳ clinical trial will be enrolled, including 90 adults aged 18-59 years and 90 elderly elderly aged 60 years and older.Subjects in each age group will receive the booster immunization of CoronaVac(the third dose) and will be collected blood sample before booster immunization and 14 days after booster immunization.

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;

Exclusion Criteria:

• History of asthma, history of allergy to the vaccine or vaccine components,or serious adverse reactions to the vaccine, such as urticaria, dyspnea,and angioedema;
• Severe neurological disease (epilepsy, convulsions or convulsions) or mental illness;
• Fever at the time of vaccination, or acute onset of chronic disease, or uncontrolled severe chronic disease, or acute disease;
• Pregnancy or lactation;
• Receipt of attenuated live vaccines in the past 14 days;
• Receipt of inactivated or subunit vaccines in the past 7 days
• According to the investigator's judgment, the subject has any other factors that are not suitable for participating in the clinical trial.