ABSTRACT
Objective @#To investigate the serum levels of antibodies against SARS-CoV-2 after inoculation of an inactivated SARS-CoV-2 vaccine, so as to provide insights into the evaluation of the vaccine immunogenicity. @*Methods @#In this single-arm Objective performance criteria trial, residents aged 18 to 59 years and inoculated with an inactivated SARS-CoV-2 vaccine in Xihu District, Hangzhou City from October to December of 2020 were selected using a cluster sampling method. Blood samples were collected prior to inoculation, 14 and 28 days post-inoculation of the first dose, and 28 days post-inoculation of the second dose. Serum levels of anti-SARS-CoV-2 IgM and IgG antibodies were detected using the magnetic particle-based chemiluminescence immunoassay. The seroconversion of antibodies and dynamic changes of antibody levels were analyzed.@*Results @#Totally 310 participants were enrolled, including 133 subjects on day 14 post-inoculation of the first dose, 97 subjects on day 28 post-inoculation of the first dose and 254 subjects on day 28 post-inoculation of the second dose. The seroconversion rates of anti-SARS-CoV-2 IgG antibody were 6.02%, 28.87% and 98.43%, and the median IgG antibody levels were 1.76 ( interquartile range, 3.25 ), 5.69 ( 9.95 ) and 52.05 ( 47.60 ) AU/mL ( P<0.05 ), respectively, while the seroconversion rates of anti-SARS-CoV-2 IgM antibody were 9.02%, 11.34% and 12.99%, and the median IgG antibody levels were 1.89 ( 3.28 ), 2.06 ( 4.71 ) and 2.65 ( 4.01 ) AU/mL ( P>0.05 ), respectively. In addition, higher serum levels of anti-SARS-CoV-2 IgG and IgM antibodies were detected post-inoculation relative to pre-inoculation ( P<0.05 ), and higher serum IgG antibody levels were found in subjects aged 18 to 39 years than in those aged 40 to 59 years ( P<0.05 ). @*Conclusions @#Inoculation of two doses of the inactivated SARS-CoV-2 vaccine achieves a high immunogenicity among residents aged 18 to 59 years 28 days post-inoculation, and the anti-SARS-CoV-2 IgM antibody is detectable in some residents following inoculation of the first dose.