BACKGROUND AND PURPOSE:

• Data regarding time course to develop antibody response to SARS-CoV-2 is limited
• Zhao et al. (Clinical Infectious Diseases, 2020) investigated the dynamics of total antibody (Ab), IgM and IgG antibodies against SARS-CoV-2 in a series of blood samples taken from patients with confirmed COVID-19

METHODS:

• Cohort study
• Setting
  • Shenzhen Third People’s Hospital, China
• Participants
  • Acute respiratory infection syndromes and/or abnormalities in chest CT images accompanied by detectable SARS-CoV-2 RNA in respiratory sample since illness onset (COVID-19 Diagnosis Based on National Health Commission of China Protocol)
  • All in critical condition requiring ventilation (invasive or non-invasive)
• Study design
  • Enzyme linked immunosorbent assays (ELISA) were performed on successive plasma samples to determine
    • Total antibodies (Ab) against SARS-CoV-2 (specificity 99.1%)
    • IgM antibody (specificity: 98.6%)
    • IgG antibody (specificity: 99.0%)
  • Antibody dynamics analyzed during disease progression

RESULTS:

• 173 patients | 535 plasma samples
• Seroconversion rate
  • Ab: 93.1%
  • IgM: 82.7%
  • IgG: 64.7%
• Negative antibody findings: 12 patients
  • These patients had samples taken earlier in their disease course (10 <day 10; 2 on day 11 and 13 after onset)
• Median seroconversion time
  • Ab: day 11
  • IgM: day 12
  • IgG: day 14
• <40% of patients had antibodies within 1 week of disease onset
• >15 days after onset, antibody testing was more sensitive, detecting a greater percentage of patients with COVID-19
  • Ab: 100%
  • IgM: 94.3%
  • IgG: 79.8%
• Combining RNA and antibody detection significantly improved sensitivity (p<0.001)
  • This was true even in the early stages of disease (<1 week since onset; p=0.007)
• A higher titer of Ab was independently associated with a worse clinical classification (p=0.006)

CONCLUSION:

• Antibodies against SARS-CoV-2 were present in 100% of COVID-19 patients after 15 days since disease onset
  • Antibodies were only detected in 40% of patients within 1 week of disease onset
• The authors highlight important points related to antibodies, including
  • This study could not evaluate the persistence of antibodies because samples were collected during the acute phase
  • Cross-reactivity of the assay to other coronaviruses needs to be further assessed
• The authors suggest that combining serological antibody tests with the PCR-based tests for viral RNA could improve the accuracy of disease diagnosis

Learn More – Primary Sources:

Antibody responses to SARS-CoV-2 in patients of novel coronavirus disease 2019

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