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

Harika Öykü Dinç

doi:10.4274/balkanmedj.galenos.2022.2021-8-131

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

Abstract

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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