Formation of SARS-CoV-2 specific antibodies in dynamics

The coronavirus disease 2019 (COVID-19) is an infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Antibody testing plays a big role in understanding virus’s epidemiology and it reveals whether a patient’s immune system has developed antibodies against the virus. The main goal of this study was to evaluate antibody response to SARS-CoV-2 in dynamics. 178 plasma samples from 154 patients (both hospitalized and outpatients) were analysed for the presence of virus-specific (IgG NCP, IgG S1 and IgA) antibodies using EUROIMMUN semi-quantitative ELISA. Plasmas samples positive for virus-specific antibodies were quantified using quantitative ELISA (ANTIBODIES) for anti-SARS-CoV-2 IgG and IgM class antibodies. In 131 COVID-19 patients’ plasma samples anti-SARS-CoV-2 IgG NCP, in 135 - anti-SARS-CoV-2 IgG S1 and in 117- anti-SARS-CoV-2 IgA class antibodies were detected. 24 patients had been tested for antibodies in dynamics (at various times after the first sampling). 7 patients’ samples were positive for IgG (7/24, 29.2%), 15 patients’ samples – for both IgM and IgG class antibodies (15/24, 62.5%). IgM level at first time point was higher than at second time point. 2 patients were SARS-CoV-2 IgM, IgA and IgG negative at first and second time point. IgA antibodies begin to appear on day 8 or 9. Approximately two weeks after infection, IgA and IgG antibodies had reached equal levels (8/24, 33.33%) and subsequently, IgA titres decreased (15/24, 62.5%), but IgG showed a tendency to decrease after two months. In one sample collected after two months, IgM antibodies had reappeared. Tendency of IgG titres to decrease after two months could indicate on an un-sustained long-term antibody response. Repeated IgM production can indicate a possible COVID-19 reinfection in some patients.