Detection of serum antibody levels after inoculation of an inactivated SARS-CoV-2 vaccine
XU Nani1, HU Xiaowei1, LI Haiyan2, ZHENG Lin1, KONG Qingxin3, QIN Pan1, LI Jing1, YE Fei4
1. Department of Immunization Program, Xihu District Center for Disease Control and Prevention, Hangzhou, Zhejiang 310030, China; 2. Hangzhou Di'an Medical Laboratory Co., Ltd, Hangzhou, Zhejiang 310012, China; 3. Hangzhou Center for Disease Control and Prevention, Hangzhou, Zhejiang 310021, China; 4. Hangzhou Xixi Hospital, Hangzhou, Zhejiang 310023, China
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.
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