Influential factor and trend of specific IgG antibody titer in coronavirus disease 2019 convalescents.

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, =22) and the low titer group (antibody titer <1꞉160, =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 CD19CD3 lymphocytes, and the treatment of glucocorticoid were not statistically significant between the patients in the high titer group and the low titer group (all >0.05). The male patients in the high titer group were more than those in the low titer group (<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.