Relationship between SARS-CoV-2 antibody titer and the severity of COVID-19

Background: It remains unclear whether high titers of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies aggravate clinical manifestations in patients or whether severe clinical manifestations result in high antibody titers. Thus, we investigated the cause–effect relationship between SARS-CoV-2 antibody titers and disease severity. Methods: We prospectively enrolled patients admitted with the diagnosis of coronavirus disease-19 (COVID-19) from February 2020 to August 2020. We measured SARS-CoV-2 antibody titers, namely anti-receptor-binding domain (RBD) antibody and neutralizing antibody (NAb), from blood samples and calculated the chest radiograph (CXR) scores of the patients to evaluate the severity of COVID-19. Results: Overall, 40 patients with COVID-19 were enrolled. Pneumonia was observed in more than half of the patients (25/40, 60%). SARS-CoV-2 antibody titers were higher in patients who were aged >60 years (anti-RBD antibodies, P = 0.003 and NAb, P = 0.009), presented with pneumonia (P = 0.006 and 0.007, respectively), and required oxygen therapy (P = 0.003 and 0.004, respectively) than in those who were not. CXR scores peaked (at 15–21 days after the onset of symptoms) statistically significantly earlier than SARS-CoV-2 antibody titers (at 22–30 days for NAb and at 31–70 days for anti-RBD antibody). There was a close correlation between the maximum CXR score and the maximum SAR-CoV-2 antibody titer. Conclusions: Based on the comparison of the peak time of SARS-CoV-2 antibody titers with the CXR score after symptom onset, we suggest that severe clinical manifestations result in high titers of SARS-CoV-2 antibodies.