SARS-CoV-2 is a newly-discovered positive-sense RNA virus, the cause of coronavirus disease 2019 (COVID-19) currently spreading worldwide. The SARS-CoV-2 S glycoprotein is considered a main target for neutralizing antibodies. In order to better understand the kinetics of the antibody response, we evaluated the relation between two consecutive antibody titers determined over an average period of four months. A total of 628 subjects were included in the study. A significant reduction of the antibody titers over time was found: Ab Titer 1: 8.1 Arbitrary Units (AU)/mL (IQR: 4.8-29.3); Ab Titer 2: 6.2 AU/mL (IQR: 0-28.5); p<0.0001. A Receiver Operator Characteristic curve analysis showed an Area Under the Curve (AUC) of 0.973 (95% CI: 0.962-0.984; p<0.0001) with an Ab titer 1 threshold of 110 AU/mL to predict an Ab Titer 2 ≥50 AU/mL with 100% specificity. Likewise, an AUC of 0.952 (95% CI: 0.930-0.974; p<0.0001) with an Ab titer 1 threshold of 185 AU/mL was found to predict an Ab Titer 2 ≥100 AU/mL. This study showed that the SARS-CoV-2 S1/S2 IgG median titer declined over an average period of four months and that the first IgG determination thresholds found can help predict IgG values after the same interval.
Keywords: COVID-19; COVID-19 Serological Testing; SARS-CoV-2.