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

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.