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COVID-19 Testing

How Long Does It Take for COVID-19 Patients to Develop Antibodies?

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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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Related ObG Topics:

Use of Convalescent Plasma in Critically Ill COVID-19 Patients: Results from a Preliminary Study
CDC Weekly Update: Which Comorbidities are Associated with COVID-19 in the US?
Infants Born to Mothers with COVID-19 Have Detectable Levels of Antibodies

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