Ultra-Sensitive Serial Profiling of SARS-CoV-2 Antigens and Antibodies in Plasma to Understand Disease Progression in COVID-19 Patients with Severe Disease

Clin Chem. 2020 Dec 1;66(12):1562-1572. doi: 10.1093/clinchem/hvaa213.


Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected over 21 million people worldwide since August 16, 2020. Compared to PCR and serology tests, SARS-CoV-2 antigen assays are underdeveloped, despite their potential to identify active infection and monitor disease progression.

Methods: We used Single Molecule Array (Simoa) assays to quantitatively detect SARS-CoV-2 spike, S1 subunit, and nucleocapsid antigens in the plasma of patients with coronavirus disease (COVID-19). We studied plasma from 64 patients who were COVID-19 positive, 17 who were COVID-19 negative, and 34 prepandemic patients. Combined with Simoa anti-SARS-CoV-2 serological assays, we quantified changes in 31 SARS-CoV-2 biomarkers in 272 longitudinal plasma samples obtained for 39 patients with COVID-19. Data were analyzed by hierarchical clustering and were compared to longitudinal RT-PCR test results and clinical outcomes.

Results: SARS-CoV-2 S1 and N antigens were detectable in 41 out of 64 COVID-19 positive patients. In these patients, full antigen clearance in plasma was observed a mean ± 95% CI of 5 ± 1 days after seroconversion and nasopharyngeal RT-PCR tests reported positive results for 15 ± 5 days after viral-antigen clearance. Correlation between patients with high concentrations of S1 antigen and ICU admission (77%) and time to intubation (within 1 day) was statistically significant.

Conclusions: The reported SARS-CoV-2 Simoa antigen assay is the first to detect viral antigens in the plasma of patients who were COVID-19 positive to date. These data show that SARS-CoV-2 viral antigens in the blood are associated with disease progression, such as respiratory failure, in COVID-19 cases with severe disease.

Keywords: SARS-CoV-2; longitudinal plasma samples; serological; single molecule arrays; viral antigen.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Antibodies, Viral / blood*
  • Antigens, Viral / blood*
  • COVID-19 / blood
  • COVID-19 / diagnosis*
  • COVID-19 Serological Testing
  • Coronavirus Nucleocapsid Proteins / blood
  • Disease Progression*
  • Female
  • Hospitalization
  • Humans
  • Intensive Care Units
  • Intubation
  • Limit of Detection
  • Male
  • Middle Aged
  • Phosphoproteins / blood
  • Prognosis
  • Protein Subunits / blood
  • SARS-CoV-2 / chemistry*
  • SARS-CoV-2 / immunology*
  • Spike Glycoprotein, Coronavirus / blood


  • Antibodies, Viral
  • Antigens, Viral
  • Coronavirus Nucleocapsid Proteins
  • Phosphoproteins
  • Protein Subunits
  • Spike Glycoprotein, Coronavirus
  • nucleocapsid phosphoprotein, SARS-CoV-2
  • spike protein, SARS-CoV-2