Persistence of Anti-SARS-CoV-2 Antibodies Following SARS-CoV-2 Infection

Abstract

Background: Since the first emergence of coronavirus disease 2019 (COVID-19) in China, elucidating the persistence and dynamics of antibody responses following infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has remained a major research priority. Objectives: To quantify serum titers of anti-SARS-CoV-2 IgM and IgG antibodies in patients with COVID-19 over a 9-month period. Methods: In this longitudinal study, blood samples were collected from 105 patients with COVID-19 who presented with mild to severe clinical manifestations at diagnosis and again at follow-up. Of these, 100 patients with complete serological data were included in the final analysis. Concentrations of anti-SARS-CoV-2-specific IgG and IgM antibodies in the collected serum samples were measured using an enzyme-linked immunosorbent assay (ELISA). Results: Of the 105 initially recruited patients, 100 (95.2%) had complete serological data and were included in the final analysis. Among all patients included in the final analysis (43 females and 57 males), 41% had severe manifestations, whereas the remainder had mild/moderate manifestations of the disease. Among all subjects, the median (interquartile range) serum IgM, baseline IgG, and follow-up IgG titers were 3.5, 10, and 4.4 cut-off index (COI), with IQRs of 5, 11.6, and 5.9, respectively. We found that approximately 81% of patients remained seropositive over the subsequent 9 months; however, the secondary IgG titer decreased from 10 to 4.4 COI relative to the primary IgG titer. Exploratory subgroup analyses suggested a slower decline in antibody levels among healthcare workers than among non-healthcare workers. However, in multivariable analysis, the baseline IgG level was the only independent predictor of antibody persistence at the 9-month follow-up. Conclusions: This study demonstrated that anti-SARS-CoV-2 antibody responses remained detectable in most patients approximately 9 months after infection. These findings provide preliminary evidence regarding the persistence of antibody responses and may have implications for vaccination strategies and the understanding of post-infection immunity.