Written informed consent was obtained from all personnel who agreed to participate. == Antibody test == Blood samples were obtained from participants before the second dose of the BNT162b2 mRNA vaccination (median: 20 days [interquartile range (IQR): 20 to 21 days] after the first dose) and 2 weeks after the second dose (median: 13 days [IQR: 11 to 14 days] after the second dose). after the second injection, when adjusted for age, sex, AE score after the first injection, and log-transformed spike IgG after the first injection. == Conclusions == Although the sample size was relatively small, reactogenicity after the second Glyburide injection may not accurately reflect antibody production. == Introduction == Effective and appropriate coronavirus disease 2019 (Covid-19) vaccination is the most promising strategy for controlling the spread of SARS-CoV2 contamination on a worldwide basis [13]. Currently, nucleoside-modified messenger RNA (mRNA) vaccines encoding SARS-CoV2 full-length spike and adenoviral vector vaccines have been used mainly in Western countries. Vaccination levels in Canada, the United States, England, and Israel are now reaching 55%69%, dramatically reducing the infection rate [47]. In Japan, the number of Covid-19 infections is usually increasing, but the vaccination rate is still low (26%) due to a limited supply of Glyburide vaccines and a slow throughput for vaccine injection. Glyburide Local and systemic reactogenicity after the second injection of mRNA vaccines is usually more common than after the first injection [1,2,8]. The second injection has a booster effect that produces substantial antibody titers against SARS-CoV2 spike antigen. Thus, we hypothesized that the degree of reactogenicity following the second injection could be an indicator of the level of SARS-CoV2 spike antibody production. Accordingly, the aim of this study was to investigate whether local and systemic reactogenicity after the second injection of an mRNA vaccine reflects subsequent SARS-CoV2 spike antibody levels in Japanese healthcare workers. == Materials and methods == == Study participants == This was a prospective, longitudinal, observational study in a single center. The study was approved by the institutional review board of the University of Occupational and Environmental Health, School of Medicine (approval number: UOEHCRB21-023). During early 2021, the only vaccine available in Japan was the BNT162b2 mRNA Covid-19 vaccine (Pfizer/BioNTech). The Japanese government started to disperse this vaccine to healthcare workers in February 2021, and our university hospital received the vaccine in the middle of March 2021. The hospital chairman decided to administer the first dose of BNT162b2 mRNA Covid-19 vaccine (30 g per dose injected into the deltoid muscle) to hospital employees during the fourth week of March and the second dose during the third CFD1 week of April (April 12 to April 16). Since we received ethical approval for the study on April 12 the time available to acquire informed consent and to conduct the study was quite short (range: 1 to 5 days), we advertised for the study participation to subjects working in four departments (Department of Laboratory and Transfusion Medicine, Department of Pathology, Department of Pharmacy, Second Department of Internal Glyburide Medicine) in the hospital. Study participation was voluntary. Participant recruitment was started on April 12 and ended on April 16. Written informed consent was obtained from all personnel who agreed to participate. == Antibody test == Blood samples were obtained from participants before the second dose of the BNT162b2 mRNA vaccination (median: 20 days [interquartile range (IQR): 20 to 21 days] after the first dose) and 2 weeks after the second dose (median: 13 days [IQR: 11 to 14 days] after the second dose). A SARS-CoV2 IgG assay was performed with chemiluminescent immunoanalysis of microparticles used for quantitative detection of IgG antibodies against the spike protein of the SARS CoV-2 computer virus (spike IgG) employing the Architect system (Abbott Diagnostics) with a cut-off <50 antibody models/mL (AU/mL) in both blood samples. To exclude the possibility of previous Covid-19 infection,.