Longitudinal Assessment of Anti-SARS-CoV-2 Immune Responses for Six Months Based on the Clinical Severity of COVID-19

Abstract

Background: There is insufficient data on the longevity of immunity acquired following severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. We aimed to evaluate the duration of SARS-CoV-2-specific humoral and cellular immunity according to the clinical severity of coronavirus disease 2019 (COVID-19).Methods: Convalescent blood was collected prospectively from 97 patients who had recovered from COVID-19. The level of humoral immunity to SARS-CoV-2 was measured using the anti-SARS-CoV-2 nucleocapsid immunoglobulin G (IgG) assay and the plaque reduction neutralization test with sera collected at three periods: within 8 weeks, at 9-20 weeks, and at 22-27 weeks after diagnosis. IFN-γ ELISpot assays were conducted using overlapping peptides covering spike, nucleocapsid, and membrane proteins of SARS-CoV-2.Findings: The study population comprised asymptomatic (n=14), symptomatic/non-pneumonic (n=42), and pneumonic (n=41) patients. The anti-SARS-CoV-2 IgG and neutralizing antibody (NAb) titers lasted until six months after diagnosis, with positivity rates of 66·7% and 86·9%, respectively. The level of humoral immunity at six months after diagnosis were significantly higher in the pneumonic group than in the symptomatic/non-pneumonic group. Older age, prolonged viral shedding and accompanying pneumonia were more frequently found in patients with sustained humoral immunity. SARS-CoV-2 specific T-cell response was strongly observed in pneumonic patients and prominent in individuals with sustained humoral immunity.Interpretation: Most (> 85%) patients carries NAb until six months after diagnosis of SARS-CoV-2 infection, providing insights for establishing vaccination strategies against COVID-19.Funding Statement: This study was supported by a grant of the Korea National Institute of Health, Korea Disease Control and Prevention Agency (project number: 2020-ER5314-00), Korea University Guro Hospital (Korea research-driven hospital) (No. O2001061), and the Korea Health Technology R&D Project through the Korea Health Industry Development Institute (KHIDI), funded by the Ministry of Health & Welfare, Republic of Korea (grant number: HI20C0452).Declaration of Interests: The authors declare no competing interests.Ethics Approval Statement: The study protocol was approved by the Institutional Review Board of the Korea University Guro Hospital (approval number: 2020GR0130). All participants provided written informed consent.