- Viral RNA was not detected in the patients' blood
- Not enough information available about the kinetics of the viral load
- Severe COVID-19 patients were excluded from this study because passive antibody therapy was administered before sample collection.

University of Michigan - Ann Arbor

Syracuse University

Virus-specific neutralizing antibodies are key in creating an immune protection against viral infections. NAbs have been widely used in the past as a passive antibody therapy for SARS-CoV and Ebola virus. They are also used in evaluating the efficacy of vaccines against smallpox, polio and influenza viruses. In this study plasma samples from 175 adult COVID-19 patients admitted to Shanghai Public Health Clinical Center were collected and then screened using a sensitive pseudotyped-lentiviral-vector-based neutralization assay. All COVID-19 patients that participated in this study had mild to common symptoms and developed peak NAbs levels 10-15 days after the onset of the disease. A wide variability in NAbs plasma levels was observed among patients.

Variations of SARS-CoV-2 specific neutralizing antibodies in recovered COVID-19 patients

Wu F, Wang A, Liu M, et al. Neutralizing antibody responses to SARS-CoV-2 in a COVID-19 recovered patient cohort and their implications. medRxiv; 2020. DOI: 10.1101/2020.03.30.20047365. 

Neutralizing Antibody Responses to SARS-CoV-2 in a COVID-19 Recovered Patient Cohort and Their Implications

From all the patients that participated in this study that were lab confirmed SARS-250
 CoV-2  infected, about 30% presented very low NAbs titers (ID50: < 500), 10 patients presented an ID50: <40 which is below the detection levels; about 17% had a showed medium-low (ID50: 500-999); 39% a medium-high ID: 1000-2500 and 14% high (ID50: > 2500) NAb titers. Two weeks after the discharge, plasma samples were taken again from these patients and no difference in NAbs titers was shown. Interestingly, a proportion of patients infected with  SARS-CoV-2  was still able to recover without developing NAbs. 

 Very low titers of SARS-CoV-2 specific NAbs observed in about 30% of patients

The data from this study suggests a positive correlation between age and NAbs titers. Elderly patients plasma samples showed significantly higher levels of spike-binding antibodies, targeting S1 and S2 compared to young patients. Furthermore, at the time of admission, elderly patients had higher blood CRP levels and lower lymphocyte counts which might suggest that the high NAbs levels in this group of patients can be due to a stronger induced innate immune response. However, there was no difference between patients' ages and the time they spent recovering in the hospital. 

High levels of SARS-CoV-2-specific NAbs in elderly and middle-age COVID-19 recovered patients

Plasma samples from COVID-19 patients contained mainly high titers of  SARS-CoV-2 RBD, S1, and S2-specific binding antibodies. Plasma from COVID-19 patients was not effective in inhibiting  SARS-CoV infection in PsV neutralization assay. However, it showed some cross-binding activity with the SARS-CoV antibodies, possibly explained by the conserved epitopes between SARS-CoV-2 and SARS-CoV spike proteins. This data suggest that the immunogenicity between SARS-CoV-2 and SARS-CoV is different. 

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