Deciphering the dynamic changes in antibodies against SARS-CoV-2 is essential for understanding the immune response in COVID-19 patients. Here we analyze the laboratory findings of 1,850 patients to describe the dynamic changes of the total antibody, spike protein (S)-, receptor-binding domain (RBD)-, and nucleoprotein (N)-specific immunoglobulin M (IgM) and G (IgG) levels during SARS-CoV-2 infection and recovery. The generation of S-, RBD-, and N-specific IgG occurs one week later in patients with severe/critical COVID-19 compared to patients with mild/moderate disease, while S- and RBD-specific IgG levels are 1.5-fold higher in severe/critical patients during hospitalization. The RBD-specific IgG levels are 4-fold higher in older patients than in younger patients during hospitalization. In addition, the S- and RBD-specific IgG levels are 2-fold higher in the recovered patients who are SARS-CoV-2 RNA negative than those who are RNA positive. Lower S-, RBD-, and N-specific IgG levels are associated with a lower lymphocyte percentage, higher neutrophil percentage, and a longer duration of viral shedding. Patients with low antibody levels on discharge might thereby have a high chance of being tested positive for SARS-CoV-2 RNA after recovery. Our study provides important information for COVID-19 diagnosis, treatment, and vaccine development.

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Coronavirus disease 2019 (COVID-19) is causing worldwide pandemic with no specific therapeutic agents, especially for severe or critical patients. To comprehensively evaluate the effectiveness, safety, and indications of convalescent plasma transfusion (CPT) therapy for severe or critical COVID-19 patients, we analyzed the clinical, laboratory, and radiologic characteristics of 1,568 patients from a single center, in which 138 patients received ABO-compatible CPT. The median time from the first symptom to CPT was 45 days. 2.2% and 4.1% of cases died in the CPT group and in the standard-treatment group, respectively. 2.4% and 5.1% of patients in the CPT and the standard-treatment group have been admitted to ICU eventually. 70% of the patients who had severe respiratory symptoms got improved and removed oxygen supports within 7 days after CPT. The viral loads and C-reactive protein (CRP) concentration significantly decreased (P<0.001), and the percentage of lymphocytes increased (P=0.006), 76.8% of cases received radiological improvements within 14 days after CPT. Patients with a higher percentage of lymphocytes and a lower percentage of neutrophils and CRP concentration respond better to CPT (P<0.05). Notably, for the patients who received CPT within 7 weeks after symptom onset, the median time from CPT to clinical improvements was approximately 10 days. But the time to clinical improvements was significantly prolonged for patients who received CPT later than 7 weeks after onset. Our study will provide important information for the clinical practice in COVID-19 treatment, as well as provide real-world observations and clinical data for the development of monoclonal antibodies.

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