Antibody responses are induced after infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Therefore, antibody tests are critical tools in the clinical management and control of SARS-CoV-2 infection and coronavirus disease 2019 (COVID-19), according to study results published in the European Respiratory Journal.

Current knowledge of the antibody response to SAR-CoV-2 infection is limited and the diagnostic value of the antibody test remains to be clearly demonstrated. Thus, researchers investigated the characteristics of antibody responses in 80 patients with COVID-19 during their hospitalization periods at the First Affiliated Hospital of Zhejiang University in China by detecting total antibodies, immunoglobulin M (IgM), and IgG using immunoassays.

Researchers found the seroconversion rates to be 98.8%, 93.8%, and 93.8% in total antibodies, IgM, and IgG, respectively. The first detectable serology marker was total antibodies, followed by IgM and IgG, with a median seroconversion time of 15, 18, and 20 days post exposure or 9, 10, and 12 days post onset, respectively. Antibody levels appeared to increase rapidly beginning at 6 days post onset and were accompanied by a decline in viral load.

For patients in the first 7 days post onset, Ab demonstrated the highest sensitivity (64.1%) compared with IgM and IgG (33.3% for both, P <.001). The sensitivities increased to 100%, 96.7%, and 93.3%, respectively, 2 weeks later No significant difference was observed between enzyme-linked immunosorbent assays and other forms of immunoassays when the same antibody type was detected. These data demonstrate that follow-up antibody testing and monitoring of respiratory symptoms for 2 weeks after de-isolation is helpful for reducing the risk of spread.

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“Serology testing provides an important complement to RNA testing in the later stages of illness for pathogenic specific diagnosis and helpful information to evaluate the adapted immunity status of patients,” the study authors concluded.


Lou B, Li T-D, Zheng S-F, et al. Serology characteristics of SARS-CoV-2 infection since exposure and post symptom onset [published online May 19, 2020]. Eur Respir J. doi:10.1183/13993003.00763-2020