LAUSR

The coronavirus disease-2019 (COVID-19) has become a global cause of death/injury, particularly for those with limited access to vaccination programs and healthcare systems. The risk of re-infection is not negligible due to the emergence of new variants and the decrease in immunity of those who have recovered COVID-19 before. In this study, it was aimed to show longitudinally the change in antibody levels of patients hospitalized for COVID-19 who had an antibody response in the early stages of their infection and to reveal a response pattern that would help to predict patients whose antibody responses decreased or persisted over time. This observational, single-center study included 38 non-critical patients admitted to COVID-19 wards. Anti-spike-1 IgG levels were investigated by the "enzyme-linked immunosorbent assay (ELISA)" method in two different samples taken at different times in each patient. Two distinct anti-spike-1 IgG antibody response patterns were detected in the study; the first pattern was that with low antibody production at first who had an increase in antibody levels after an average of six months, and the second pattern was that the initially high antibody levels decreased after an average of six months. This paradoxical kinetic may blur physicians' predictions of antibody response. In general, anti-spike-1 antibody levels showed a moderate decrease after six months, but production seems to continue (mean ∆IgG= -0.77; σ= 4; p= 0.24). Higher antibody levels were observed at the beginning in patients with concomitant bacterial pneumonia (mean initial IgG= 7.67; σ= 3.54) (p= 0.03). Although the production of S1-IgG in patients recovered from severe acute respiratory system coronavirus2 (SARS-CoV-2) was modestly reduced compared to the beginning measurements, the production in general persisted during the study period. It appears that IgG responses increase or remain constant in individuals with relatively low IgG index values when controlled after an average of 180 days, while IgG tends to decrease in individuals with high IgG index values.