Neutralizing Antibodies Responses to SARS-CoV-2 in COVID-19 Inpatients and Convalescent Patients.

BACKGROUND: COVID-19 is a pandemic with no specific antiviral treatments or vaccines. The urgent needs for exploring the neutralizing antibodies from patients with different clinical characteristics are emerging. METHODS: A total of 117 blood samples were collected from 70 COVID-19 inpatients and convalescent patients. Antibodies were determined with a modified cytopathogenic neutralization assay (NA) based on live SARS-CoV-2 and enzyme linked immunosorbent assay (ELISA). The dynamics of neutralizing antibody levels at different time points with different clinical characteristics were analyzed. RESULTS: The seropositivity rate reached up to 100.0% within 20 days since onset, and remained 100.0% till day 41-53. The total GMT was 1:163.7 (95% CI, 128.5 to 208.6) by NA and 1:12441.7 (95% CI, 9754.5 to 15869.2) by ELISA. The antibody level by NA and ELISA peaked on day 31-40 since onset, and then decreased slightly. In multivariate GEE analysis, patients at age of 31-45, 46-60, and 61-84 had a higher neutralizing antibody level than those at age of 16-30 (�=1.0470, P=0.0125; �=1.0613, P=0.0307; �=1.3713, P=0.0020). Patients with a worse clinical classification had a higher neutralizing antibody titer (�=0.4639, P=0.0227). CONCLUSIONS: The neutralizing antibodies were detected even at the early stage of disease, and a significant response showed in convalescent patients.