Characterization of QuantiFERON Severe Acute Respiratory Syndrome Coronavirus 2 and Anti-severe Acute Respiratory Syndrome Coronavirus 2 Nucleocapsid and S1 Spike Protein Antibodies in Vaccinated and Unvaccinated Coronavirus Disease 2019 Patients

Background: Coronavirus disease 2019 (COVID-19) vaccination has been shown to elicit both humoral (antibody) and cell-mediated (T-cell) immune responses. This study aimed to characterize and compare the QuantiFERON severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and anti-SARS-CoV-2 antibody responses in vaccinated and unvaccinated COVID-19 patients, as well as vaccinated healthy controls (HCs). Methods: A total of 96 COVID-19 patients (68 vaccinated with Sinopharm and 15 with AstraZeneca), 13 unvaccinated COVID-19 patients, and 16 vaccinated HCs (8 Sinopharm and 8 AstraZeneca) were included. Serum antibodies against the SARS-CoV-2 spike (S1) protein and nucleocapsid (N) protein were measured by enzyme-linked immunosorbent assay. T-cell responses were evaluated using the QuantiFERON assay against three SARS-CoV-2 viral antigens (Ag1, Ag2, and Ag3). Results: There were no significant differences in S1 antibody levels between COVID-19 patients (vaccinated or unvaccinated) and HCs. However, 100 of unvaccinated COVID-19 patients had anti-N antibodies, which was significantly higher than the AstraZeneca-vaccinated group. T-cell responses did not differ significantly between vaccinated and unvaccinated patients or between vaccinated patients and HCs. Vaccination with Sinopharm induced higher levels of total N antibodies and greater interferon-gamma release against the viral antigens compared to the other groups. Conclusions: Vaccination, especially with Sinopharm, induced robust humoral (N antibodies) and cellular (T-cell) immune responses in COVID-19 patients. The findings highlight the importance of vaccination in eliciting a comprehensive immune response against SARS-CoV-2, even in the context of prior infection. Keywords: Antibody, severe acute respiratory syndrome coronavirus 2, SINO, spike protein, vaccine