Quantitative Measurement of the SARS-CoV-2 IgG Antibody and Surrogate Neutralizing Antibody Responses among mRNA COVID-19 Vaccine-Inoculated Medical Staff in Designated Medical Institutions for Infectious Diseases

This study was aimed at evaluating the changes in the antibody titers and neutralization ability before and after inoculation with an mRNA COVID-19 vaccine (Pfizer, USA) among healthcare professionals (HCPs) in Japan. A total of 221 HCPs were enrolled and their blood samples were collected at three time points: 1) before vaccination, 2) 3 weeks after the first dose, and 3) 3 weeks after the second dose. The titers of anti-SARS-CoV-2 Spike protein IgG antibody were measured in all the samples using VITROS-Anti-SARS-CoV-2 S1 Quant IgG Antibody (CLEIA, Ortho-Clinical Diagnostics, Inc. ), and the surrogate Virus Neutralization Test (sVNT) (ELISA, GenScript, USA) was performed in the samples obtained after the vaccination. The anti-SARS-CoV-2 IgG titers were 1) median: 0.16; Interquartile (IQR): 0.10-0.27, 2) median: 250; IQR: 99.5-466 and 3) median: 2,400; IQR: 1,480-3,950, respectively, at the three time-points. Our study also revealed the relationship between the anti-SARS-CoV-2 IgG antibody titer and the antibody neutralization activity.