Early detection of neutralizing antibodies against SARS-CoV-2 in COVID-19 patients in Thailand

PLoS One. 2021 Feb 12;16(2):e0246864. doi: 10.1371/journal.pone.0246864. eCollection 2021.


Background: The presence of neutralizing antibodies (NAbs) is an indicator of protective immunity for most viral infections. A newly developed surrogate viral neutralization assay (sVNT) offers the ability to detect total receptor binding domain-targeting NAbs in an isotype-independent manner, increasing the test sensitivity. Thus, specimens with low IgM/ IgG antibody levels showed strong neutralization activity in sVNT.

Methods: This study aimed to measure the %inhibition of NAbs measured by sVNT in PCR-confirmed COVID-19 patients. The sensitivity of sVNT for the diagnosis of SARS-CoV-2 infection and its kinetics were determined.

Results: Ninety-seven patients with PCR-confirmed SARS-CoV-2 infection were included in this study. Majority of the patients were 21-40 years old (67%) and 63% had mild symptoms. The sensitivity of sVNT for the diagnosis of SARS-CoV-2 infection was 99% (95% confidence interval (CI) 94.4-100%) and the specificity was 100% (95% CI 98.3-100%). The negative predictive value of sVNT from the samples collected before and after 7 days of symptom onset was 99.5% (95% CI 97.4-100%) and 100% (95% CI 93.8-100%), respectively. The level of inhibition at days 8-14 were significantly higher than days 0-7 (p<0.001). The median %inhibition values by severity of COVID-19 symptoms were 79.9% (interquartile range (IQR) 49.7-91.8%); 89.0% (IQR 71.2-92.4%); and 86.6% (IQR 69.5-92.8%), for mild, moderate and severe/critical symptoms respectively. The median level of sVNT %inhibition of severe was significantly higher than the mild group (p = 0.05).

Conclusion: The sVNT is a practical and robust serological test for SARS-CoV-2 infection and does not require specialized biosafety containment. It can be used clinically to aid diagnosis in both early and late infection especially in cases when the real-time RT-PCR results in weakly negative or weakly positive, and to determine the protective immune response from SARS-CoV-2 infection in patients.

Publication types

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

MeSH terms

  • Adult
  • Antibodies, Neutralizing / analysis
  • Antibodies, Neutralizing / isolation & purification*
  • Antibodies, Viral / isolation & purification
  • COVID-19 / diagnosis*
  • COVID-19 / immunology
  • COVID-19 Nucleic Acid Testing
  • COVID-19 Serological Testing / methods*
  • Female
  • Humans
  • Male
  • Middle Aged
  • Neutralization Tests / methods*
  • SARS-CoV-2 / physiology*
  • Sensitivity and Specificity
  • Serologic Tests
  • Spike Glycoprotein, Coronavirus / chemistry
  • Thailand
  • Young Adult


  • Antibodies, Neutralizing
  • Antibodies, Viral
  • Spike Glycoprotein, Coronavirus
  • spike protein, SARS-CoV-2