immunogenicity and safety of a third dose of covid-19 vaccine(vero cell), inactivated in the elderly

Conditions: COVID-19

Summary: this is an open phase ⅲ clinical trial of covid-19 vaccine (vero cell), inactivated manufactured by sinovac research \& development co., ltd.the purpose of this study is to evaluate immunogenicity and safety of a third dose at different times after two-dose of covid-19 vaccine (vero cell), inactivated in the elderly aged 60 years and above.

this study is an open phase ⅲ clinical trial. the main purpose of this study is to evaluate immunogenicity and safety of a third dose at different times after two-dose of covid-19 vaccine (vero cell), inactivated manufactured by sinovac research \& development co., ltd. in the elderly aged 60 years and above.a total of 400 subjects aged 60 years and above who had received two doses of covid-19 vaccine(vero cell), inactivated manufactured by sinovac research \& development co., ltd. between 3 - 6 months ago (100 subjects for 3 months, 4 months, 5 months and 6 months,respectively) will be enrolled and receive a third dose of two-dose of covid-19 vaccine (vero cell), inactivated were enrolled.

Eligibility criteria:
inclusion criteria: * subjects aged 60 years and above; * provide legal identification; * have completed two-dose of covid-19 vaccine (vero cell), inactivated manufactured by sinovac research\& development co., ltd. for 3\~6 months（the interval between two doses was 21\~35 days）； * be able to understand and voluntarily sign the informed consent form and be willing to complete the study according to the research plan. exclusion criteria: * history of sars-cov-2 infection(laboratory confirmed); * those who have received covid-19 vaccine from other manufacturers other than sinovac research\& development co., ltd., or who have received booster immunization with covid-19 vaccine after two doses of covid-19 vaccine (vero cell),inactivated manufactured by sinovac research\& development co., ltd.; * history of serious adverse reactions to the vaccine or vaccine components, such as urticaria dyspnea and angioneuroedema; * autoimmune disease or immunodeficiency/immunosuppression; * severe chronic diseases, severe cardiovascular diseases, hypertension and diabetes that cannot be controlled by drugs, liver or kidney diseases, malignant tumors, etc; * severe neurological disease (epilepsy, convulsions or convulsions) or mental illness; * immunosuppressive therapy, cytotoxic therapy, inhaled corticosteroids(excluding allergic rhinitis corticosteroid spray therapy, acute noncomplicated dermatitis superficial corticosteroid therapy) in the past 6 months or plan to receive these treatments during the study period; * receipt of blood products within in the past 3 months or plan to receive these treatments during the study period; * receipt of other investigational drugs in the past 30 days; * receipt of attenuated live vaccines in the past 14 days,or receipt of inactivated or subunit vaccines in the past 7 days; * onset of various acute or chronic diseases within 7 days prior to the study; * axillary temperature \>37.0°c; * according to the investigator's judgment, the subject has any other factors that are not suitable for participating in the clinical trial.