Serum antibody levels in COVID-19 patients six months after hospital discharge

ObjectiveTo investigate the level of serum antibodies in COVID-19 patients six months after discharge， and to provide data to evaluate the duration of IgM， IgG and neutralizing antibody titers in the patients.

MethodsEnzyme-linked immunosorbent assay （ELISA） was used to determine the antibody levels of IgM and IgG， and the new coronavirus live virus neutralization test was used to detect the neutralizing antibodies in the plasma of 181 recovered patients.

ResultsThe IgG positive rate was 92.27% （167/181） in COVID-19 patients six months after discharge， while the lgM positive rate was 28.18% （51/181）. Six months after hospital discharge， 117 recovered patients （64.64%） were positive for IgG antibodies and negative for IgM antibodies， indicating that they had produced stable antibodies. This result suggested that they had been infected with the new coronavirus （SARS-CoV-2） and were in the recovery stage. The positive detection rate of neutralizing antibodies was as high as 91.71%.

ConclusionSix months after infection with SARS-CoV-2， IgG antibodies produced in the patients continue to exist， and the neutralizing antibodies maintain a high and stable level. Results of this study have important guiding significance for future research on the durability of new coronavirus antibodies.