ISSN : 2146-3123
E-ISSN : 2146-3131

Anti-SARS-CoV-2 IgG and Neutralizing Antibody Levels in Patients with Past COVID-19 Infection: A Longitudinal Study
Harika Öykü Dinç1, Mehmet Demirci2, Yusuf Emre Özdemir3, Serhat Sirekbasan4, Ayse Nur Aktaş5, Rıdvan Karaali5, Yeşim Tuyji Tok6, Doğukan Özbey6, Rüveyda Akçin6, Nesrin Gareayaghi7, Mert Ahmet Kuşkucu7, Kenan Midilli6, Gökhan Aygün6, Suat Sarıbaş6, Bekir Kocazeybek6
1Department of Pharmaceutical Microbiology, Pharmacy Faculty, Bezmialem Vakıf University, İstanbul, Turkey
2Department of Medical Microbiology Faculty, of Medicine, Kırklareli University, Kırklareli, Turkey
3Specialist of Infectious Diseases and Clinical Microbiology, University of Health Sciences Turkey Bakırköy Sadi Konuk Training Research Hospital, İstanbul, Turkey
4Department of Medical Laboratory, Techniques Çankırı Karatekin University, Eldivan Vocational School of Health Services, Çankırı, Turkey
5Department of Infectious Diseases and Clinical Microbiology, Cerrahpasa Faculty of Medicine, İstanbul University-Cerrahpaşa, İstanbul, Turkey
6Department of Medical Microbiology, Cerrahpaşa Faculty of Medicine, İstanbul University-Cerrahpaşa, İstanbul, Turkey
7Blood Center İstanbul Şişli Hamidiye Etfal Training and Research Hospital, İstanbul, Turkey
DOI : 10.4274/balkanmedj.galenos.2022.2021-8-131
Pages : 172-177


Background: 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.
Aims: 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).
Study Design: A longitudinal study.
Methods: 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.
Results: 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, p = 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 (p = 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 (p = 0.018), but without significant differences between severe and moderate or mild COVID-19.
Conclusion: 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.

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