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First Author: Huan Ma et al. 

Journal/preprint name: MedRxiv 

Tags: Immunology/Immunity, Clinical/Diagnostics, Serology 


Ma et al. measured the levels of IgG, IgM and IgA against SARS-CoV-2 RBD for 27 COVID-19 convalescent patients (1 critically ill, 4 severe, 20 moderate and 2 mild patients) on the day of discharge from hospital and on a voluntary revisit 28-99 days (median 91 days) later. A significant reduction in RBD-specific antibody levels was observed overall, and patients with low levels of antibodies at hospital discharge remained low at revisit. Finally, an exponential decay model of antibody kinetics following infection was used to predict the number of days post hospital discharge when RBD-specific antibodies would reach undetectable levels. 

Research Highlights

  1. Observed that after 90 days post discharge from hospital, symptomatic patients had a significant decrease in RBD-specific IgG, IgM and IgA. 

  1. Predicted RBD-specific IgG to become seronegative 273 days, IgM 150 days and IgA 108 days post hospital discharge.   

  1. Observed that symptomatic patients being discharged from hospital with low RBD-specific antibody levels, remained low at revisit. 

Impact for COVID-19 research:  

  • Observed that symptomatic patients 90 days after discharge from hospital had a significant decrease in RBD-specific antibody levels which may have an impact on long-term immunity for infected individuals 


  • Study Type: Cohort study 

  • Important cell lines/viral models used: SARS-CoV-2 

  • Key Techniques: PCR, previously established chemiluminescence kit detecting RBD-specific antibodies  


  • Small number of patients. 

  • Number of repeats for each sample is not mentioned or was not carried out. 

  • Would have been interesting to have investigated antibody responses to the whole spike protein of SARS-CoV-2 rather than just the RBD. 

  • Would have been interesting to have measured the antibody responses at additional time points (the majority were at >85 days post hospital discharge with a few at 29-38 days), for example at 50-70 days or a later time point than 100 days – this might also increase the accuracy of their antibody seronegative predictions. 

  • Would have been informative to have also examined cellular immune responses in the patients.