- subjects were previously confirmed cases of covid-19 or asymptomatic infected persons; - being allergic to any component of vaccines (including excipients) ; - injection of non-specific immunoglobulin within 1 month before enrollment; - injection of live attenuated vaccines within 1 month and injection of other vaccines within 14 days before enrollment; - subjects who have experienced severe allergic reactions to vaccines (e.g. acute anaphylaxis, urticaria, angioneurotic edema, dyspnea, etc.); - having uncontrolled epilepsy and other progressive neurological disorders and a history of guillain-barre syndrome; - having severe liver and kidney diseases, malignant tumors, acute diseases or acute episodes of chronic diseases; - have been diagnosed with congenital or acquired immunodeficiency, hiv infection, lymphoma, leukaemia or other autoimmune diseases; - have been diagnosed with thrombocytopenia or other clotting disorders that may contraindicate subcutaneous injection; - during an acute episode of chronic bronchitis/chronic obstructive pulmonary disease; - subjects who had vaccine-related adverse reactions after the second dose; - having high fever (axillary temperature ≥39.0℃) for three days after the second dose of inoculation, or severe allergic reaction; - having any adverse nervous system reaction after the second dose; - during the acute onset of a chronic disease, or the recovery of acute complications less than two weeks; - other reasons for exclusion considered by the investigator.

- subjects were previously confirmed cases of covid-19 or asymptomatic infected persons; - being allergic to any component of vaccines (including excipients) ; - injection of non-specific immunoglobulin within 1 month before enrollment; - injection of live attenuated vaccines within 1 month and injection of other vaccines within 14 days before enrollment; - subjects who have experienced severe allergic reactions to vaccines (e.g. acute anaphylaxis, urticaria, angioneurotic edema, dyspnea, etc.); - having uncontrolled epilepsy and other progressive neurological disorders and a history of guillain-barre syndrome; - having severe liver and kidney diseases, malignant tumors, acute diseases or acute episodes of chronic diseases; - have been diagnosed with congenital or acquired immunodeficiency, hiv infection, lymphoma, leukaemia or other autoimmune diseases; - have been diagnosed with thrombocytopenia or other clotting disorders that may contraindicate subcutaneous injection; - during an acute episode of chronic bronchitis/chronic obstructive pulmonary disease; - subjects who had vaccine-related adverse reactions after the second dose; - having high fever (axillary temperature ≥39.0℃) for three days after the second dose of inoculation, or severe allergic reaction; - having any adverse nervous system reaction after the second dose; - during the acute onset of a chronic disease, or the recovery of acute complications less than two weeks; - other reasons for exclusion considered by the investigator.