Persistence assessment of SARS-CoV-2-specific IgG antibody in recovered COVID-19 individuals and its association with clinical symptoms and disease severity: A prospective longitudinal cohort study.

Abstract Background Antibodies play an important role in neutralizing invading pathogens and protecting the host against re-infection. Thus, the accurate assessment of antibodies during a pandemic can provide important evidence for monitoring pathogen exposure, understanding the role of antibodies in protective immunity, and helping vaccine development. Methods In this study, 96 west Iranian recovered COVID-19 subjects were recruited and, based on clinical symptoms and disease severity, categorized into three different groups: mild, moderate, and severe. In addition, the presence and dynamic change of SARS-CoV-2-specific IgG antibody three, four-, and six months post symptom onset (PSO) were measured. Also, the association between IgG antibody titer with clinical symptoms and disease severity was examined. Results Although in real-time RT-PCR-positive samples negative IgG antibody results were found, most subjects mount humoral immune responses that could raise a robust SARS-CoV-2-specific IgG antibody. Furthermore, this antibody persisted in the serum of most recovered COVID-19 subjects at least six months PSO and demonstrated little to no decrease. Also, specific IgG antibody titer was strongly correlated with clinical symptoms and disease severity. Conclusions These results provide an insight into the presence and persistence of the SARS-CoV-2-specific IgG antibody. Although serological tests could not be used as the primary diagnostic test, they may support real-time RT-PCR results. Also, they could be used for diagnosing COVID-19 subjects tested later outside of the optimal period. Thus, the SARS-CoV-2-specific IgG antibody is an excellent marker of COVID-19 infection or vaccination and provides an additional diagnostic tool for verifying results and helps monitor and control COVID-19 spread.