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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.
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Objective:To evaluate the in vitro cross-neutralization of serum antibodies in human and mice immunized with inactivated SARS-CoV-2 vaccine against Delta and Beta variants. Methods:Human serum samples after a second and a third dose of inactivated SARS-CoV-2 vaccine and mouse serum samples after a two-dose vaccination were collected. The neutralizing antibodies in the samples against SARS-CoV-2 strains of prototype, Delta and Beta variants were detected using micro-neutralization assay in biosafety level Ⅲ laboratory. The seroconversion rates and geometric mean titers (GMTs) of antibodies were calculated.Results:The seroconversion rates of antibodies in human serum samples against different SARS-CoV-2 strains were all above 95%. After two-dose vaccination, the GMTs of neutralizing antibodies against the prototype, Delta and Beta strains were 109, 41 and 15, respectively. The GMTs decreased by 2.7 folds and 7.3 folds for the Delta and Beta variants as compared with the prototype strain. After the booster vaccination, the GMTs of neutralizing antibodies against the prototype, Delta and Beta strains were 446, 190 and 86, respectively. The GMTs of neutralizing antibodies against Delta and Beta variants decreased by 2.3 folds and 5.2 folds as compared with that against the prototype strain. The seroconversion rates of antibodies against different SARS-CoV-2 strains in mouse serum samples were all 100%. The GMTs of neutralizing antibodies against the prototype, Delta and Beta strains were 2 037, 862 and 408, respectively. The GMTs decreased by 2.4 folds and 5.0 folds for the Delta and Beta variants.Conclusions:Inactivated SARS-CoV-2 vaccine could induce a certain level of neutralizing antibodies against Delta and Beta variants in both human and mouse models. Moreover, a third dose of vaccine induced higher levels of neutralizing antibodies against Delta and Beta variants in human. This study provided valuable data for the clinical application and protective evaluation of the inactivated SARS-CoV-2 vaccine.