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Objectives: To explore the influential factors and titer trend of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) specific IgG antibody in convalescent patients with coronavirus disease 2019 (COVID-19), and to provide theoretical basis for the feasibility of clinical treatment of convalescent plasma., Methods: Colloidal gold immunochromatography assay was used to detect the SARS-CoV-2 specific IgG antibody and its titer in 113 convalescent patients with COVID-19 who were followed up from February 19, 2020 to April 6, 2020. The basic characteristics and treatment factors of patients in the high titer group (antibody titer≥1꞉160, n =22) and the low titer group (antibody titer <1꞉160, n =91) were analyzed. The IgG antibody titer in the high titer group was continuously monitored and the trend of titer was analyzed., Results: The difference in the clinical type of COVID-19, onset time, first admission C-reactive protein, absolute value of lymphocyte, absolute value of CD19 + CD3 - lymphocytes, and the treatment of glucocorticoid were not statistically significant between the patients in the high titer group and the low titer group (all P >0.05). The male patients in the high titer group were more than those in the low titer group ( P <0.05). The titer of SARS-CoV-2 specific IgG antibody in the high titer group decreased to less than 1꞉160 28 d after discharge., Conclusions: Male COVID-19 patients might be more likely to produce high titer SARS-CoV-2 specific IgG antibodies than female. The peak level of SARS-CoV-2 specific IgG antibody in convalescent patients is maintained for a short period. Using plasma from convalescent COVID-19 patients for treatment should be within 28 d after discharge.

Objectives: To evaluate curative effects of coronavirus disease 2019 (COVID-19) patients by the transfusion of other convalescent plasma., Methods: Retrospective analysis of the clinical data of 18 patients with severe and critical COVID-19, who were hospitalized in the ICU of Xianghu Branch of the First Affiliated Hospital of Nanchang University from February 1 to March 15, 2020. Patients were subdivided into an experimental group ( n =6, who had transfused the plasma) and an observation group ( n =12, who had no plasma transfusion). Basic clinical data and prognosis indexes of these two groups were compared. Moreover, for the experimental group, the dynamic changes of blood oxygen saturation before and after the transfusion, the changes of lymphocyte absolute value 48 hours after the transfusion, and the detection of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleic acid were analyzed., Results: There were no significant differences in age, gender, blood type and other basic clinical data between the two groups (all P >0.05).There were no significant differences in ventilator machine weaning time, extracorporeal membrane oxygenation (ECMO) weaning time, body temperature recovery to normal time, and hospitalization days between these two groups (all P >0.05). For the experimental group, before, during and after the convalescent plasma transfusion, the blood oxygen saturation of all 6 patients at all time (1, 6, 8, 12, 24, 36, and 48 h) was more than 90%, and there was no significant fluctuation. There were 3 patients whose absolute value of lymphocyte was increased 48 hours after the transfusion, and the remaining was decreased. There were 5 patients whose SARS-CoV-2 nucleic acid detection turned negative 48 hours after the transfusion, accounting for 83.3%., Conclusions: Transfusion of convalescent plasma will not affect outcomesof COVID-19 patients, which can neutralize SARS-CoV-2 in patients and reduce the loading capacity of SARS-CoV-2.