Long-term serological SARS-CoV-2 IgG kinetics following mRNA COVID-19 vaccine: real-world data from a large cohort of healthcare workers

Objectives: This study aimed to assess kinetics and predictive variables of humoral immune response to mRNA SARS-CoV-2 vaccine administration.Methods: We collected blood samples before (T0) and 15, 90, and 180 days after vaccination (T1, T2, and T3, respectively). The Quant SARS-CoV-2 Immunoglobulin (IgG) II Chemiluminescent Microparticle Immunoassay was used to determine anti-spike IgG.Results: In almost 30 0 0 healthcare-collected blood samples at the three time points, we found the following: at 15 days postvaccination, 97.6% of subjects presented a robust IgG anti-spike response ( > 4160 AU/ml); then, at three and six months, it decreased in median 6.5-fold to 35.0% and 3.0-fold to 3.3%, respectively. A linear mixed-effects model supported that female gender, younger age groups, and being seropositive prevaccination maintained higher antibody titers. Curves became tighter with time progression, although titers from seropositive subjects decrease at a slower rate than seronegative ones.Conclusion: These findings strengthen the case for a steep decrease of anti-SARS-CoV-2 antibodies up to six months, suggesting that serological evaluation might guide the need for periodic booster vaccinations in specific groups prone to lower antibody titers.(c) 2022 The Authors. Published by Elsevier Ltd on behalf of International Society for Infectious Diseases. This is an open access article under the CC BY-NC-ND license ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )