This study is a randomized, double-blinded clinical Trial, to evaluate the non-inferiority of the commercial scale Inactivated SARS-CoV-2 vaccine against that of the pilot scale among adults aged 26-45 years, and the open-labelled, bridging non-inferiority of the vaccine induced immunogenicity in elderly against that in adults. The experimental vaccine was manufactured by Sinovac Research \& Development Co.,Ltd. Totally 1040 subjects，including: 130 subjects aged 18\~25 years; 520 subjects aged 26\~45 years, with 260 in each group; 130 subjects aged 46\~59 years; 260 subjects aged ≥60 years.
Subjects will be assigned to receive two doses of medium-dosage vaccine on the schedule of 0,14.
