Anti-SARS-CoV-2 IgG and Neutralizing Antibody Levels in Patients with Past COVID-19 Infection: A Longitudinal Study

• Published in: Balkan medical journal Vol. 39; no. 3; pp. 172 - 177
• Main Authors: Dinç, Harika Öykü, Demirci, Mehmet, Özdemir, Yusuf Emre, Sirekbasan, Serhat, Aktaş, Ayse Nur, Karaali, Rıdvan, Tuyji Tok, Yeşim, Özbey, Doğukan, Akçin, Rüveyda, Gareayaghi, Nesrin, Kuşkucu, Mert Ahmet, Midilli, Kenan, Aygün, Gökhan, Sarıbaş, Suat, Kocazeybek, Bekir
• Format: Journal Article
• Language: English
• Published: Turkey Galenos Yayinevi Tic. Ltd 24-05-2022; Galenos Publishing; Galenos Publishing House
• Subjects: Antibodies, Neutralizing; Antibodies, Viral; COVID-19; Health aspects; Humans; Immune response; Immunoglobulin G; Longitudinal Studies; Original; Physiological aspects; SARS-CoV-2; Turkey
• ISSN: 2146-3123; 2146-3131
• DOI: 10.4274/balkanmedj.galenos.2022.2021-8-131

Monitoring the longevity of immunoglobulin G (IgG) responses following severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infections is vital to understanding the role of antibodies in preventing infection.
To determine the quantitative IgG responses specific to the Spike-S1 (S1) receptor-binding domain (S1/RBD) region of the virus in serum samples taken between 4 weeks and 7 months after polymerase chain reaction (PCR) positivity in patients who are diagnosed with coronavirus disease-2019 (COVID-19).
A longitudinal study.
This study included 113 patients with a clinical and molecular diagnosis of COVID-19. The first and second serum samples were taken 1 and 7 months, respectively, after the PCR positivity. S1/RBD-specific IgG antibody response was assayed using anti-SARS-CoV- 2 QuantiVac ELISA (IgG) kit (Euroimmun, Lübeck, Germany). The neutralizing antibodies were investigated in 57 patients whose IgG test results were above the cut-off value.
In 57 patients with SARS-CoV-2 IgG, the anti-SARS-CoV-2 IgG quantitative antibody levels significantly decreased after 7 months (Z = −2.197,
= 0.028). A correlation was detected between the anti-SARS-CoV-2 IgG and nAb percent inhibition (IH%) levels detected in 1 month (rs = 0.496, p < 0.001), but without significant correlation in serum samples taken on 7 months. The nAb IH% levels of the first and second were compared for COVID-19 severity and revealed no statistical difference (
= 0.256). In the second serum sample, the nAb IH%s of patients with moderate COVID-19 showed a statistically significant difference from patients with mild COVID-19 (
= 0.018), but without significant differences between severe and moderate or mild COVID-19.
SARS-CoV-2 quantitative IgG antibody titers are significantly reduced at long-term follow-up (> 6 months). Due to the limited information on seroconversion, comprehensive studies should be conducted for long-term follow-up of the immune response against SARS-CoV-2.