Viral Dynamics and Immune Correlates of Coronavirus Disease 2019 (COVID-19) Severity

Clin Infect Dis. 2021 Nov 2;73(9):e2932-e2942. doi: 10.1093/cid/ciaa1280.


Background: Key knowledge gaps remain in the understanding of viral dynamics and immune response of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection.

Methods: We evaluated these characteristics and established their association with clinical severity in a prospective observational cohort study of 100 patients with PCR-confirmed SARS-CoV-2 infection (mean age, 46 years; 56% male; 38% with comorbidities). Respiratory samples (n = 74) were collected for viral culture, serum samples for measurement of IgM/IgG levels (n = 30), and plasma samples for levels of inflammatory cytokines and chemokines (n = 81). Disease severity was correlated with results from viral culture, serologic testing, and immune markers.

Results: Fifty-seven (57%) patients developed viral pneumonia, of whom 20 (20%) required supplemental oxygen, including 12 (12%) with invasive mechanical ventilation. Viral culture from respiratory samples was positive for 19 of 74 patients (26%). No virus was isolated when the PCR cycle threshold (Ct) value was >30 or >14 days after symptom onset. Seroconversion occurred at a median (IQR) of 12.5 (9-18) days for IgM and 15.0 (12-20) days for IgG; 54/62 patients (87.1%) sampled at day 14 or later seroconverted. Severe infections were associated with earlier seroconversion and higher peak IgM and IgG levels. Levels of IP-10, HGF, IL-6, MCP-1, MIP-1α, IL-12p70, IL-18, VEGF-A, PDGF-BB, and IL-1RA significantly correlated with disease severity.

Conclusions: We found virus viability was associated with lower PCR Ct value in early illness. A stronger antibody response was associated with disease severity. The overactive proinflammatory immune signatures offer targets for host-directed immunotherapy, which should be evaluated in randomized controlled trials.

Keywords: COVID-19; cytokines; immunology; serology; viral culture.

Publication types

  • Observational Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies, Viral
  • COVID-19*
  • Female
  • Humans
  • Immunoglobulin M
  • Male
  • Middle Aged
  • Pneumonia, Viral*
  • Prospective Studies
  • SARS-CoV-2
  • Seroconversion


  • Antibodies, Viral
  • Immunoglobulin M