BACKGROUND: This study examined the safety and immunogenicity of an inactivated SARS-CoV-2 vaccine .
METHOD: In a phase I randomized, double-blinded, placebo-controlled trial involving 192 healthy adults 18-59 years old, two injections of three doses (50 EU , 100 EU , 150 EU) of an inactivated SARS-CoV-2 vaccine or placebo were administered intramuscularly at a 2- or 4-week interval . The safety and immunogenicity of the vaccine were evaluated .
RESULTS: Vaccination was completed in 191 subjects . Forty-four adverse reactions occurred within 28 days, most commonly mild pain and redness at the injection site or slight fatigue . At days 14 and 28, the seroconversion rates were 87.5% and 79.2% (50 EU), 100% and 95.8% (100 EU), and 95.8% and 87.5% (150 EU), respectively, with geometric mean titers (GMTs) of 18.1 and 10.6 , 54.5 and 15.4, and 37.1 and 18.5, respectively, for the schedules with 2-week and 4-week intervals . Seroconversion was associated with synchronous upregulation of antibodies against the S protein, N protein and virion and a cytotoxic T lymphocyte (CTL) response . No cytokines and immune cells related to immunopathology were observed . Transcriptome analysis revealed the genetic diversity of immune responses induced by the vaccine . INTERPRETATION: In a population aged 18-59 years in this trial, this inactivated SARS-CoV-2 vaccine was safe and immunogenic .
TRIAL REGISTRATION: CTR20200943 and NCT04412538.