Anti-SARS-CoV-2 IgG antibody response among Indian COVID-19 patients using β-propiolactone-inactivated, whole virus-based indirect ELISA

J Virol Methods. 2021 Jan:287:113996. doi: 10.1016/j.jviromet.2020.113996. Epub 2020 Oct 22.


Background: Coronavirus disease 2019 (COVID-19) pandemic caused by infection with severe acute respiratory syndrome - coronavirus-2 (SARS-CoV-2) continues to affect many countries and large populations. Serologic assays for antibody detection aid patient diagnosis and seroepidemiologic investigations.

Methods: An indirect IgG ELISA was developed indigenously using β-propiolactone (BPL) inactivated SARS-CoV-2. This assay was used for screening 200 healthy donor sera collected prior to COVID-19 emergence (2017-2019), 185 serum/plasma samples of confirmed COVID-19 patients (n = 137) and 57 samples of viral RNA positive asymptomatic contacts (n = 51). The IgG response was studied in relation to duration and severity of illness.

Results: The ELISA demonstrated 97 % specificity and IgG detection in >50 %, 80 %, 93.8 % and 100 % of the patients respectively during the first, second, third and fourth week of illness. IgG detection rate was higher in patients with severe disease (SD, 90.9 %) than those with mild disease (MD, 68.8 %) during the second week of illness (P = 0.027). IgG seropositivity among asymptomatic contacts was 64.7 %. IgG ELISA absorbance values were higher in SD than MD patients during the first 2 weeks of illness (P < 0.05). No significant difference was observed between the absorbance values of asymptomatic subjects and MD patients (P = 0.94).

Conclusion: The BPL inactivated virus-based ELISA could detect IgG antibodies early and in a significant proportion of COVID-19 patients suggesting its potential utility as a supplement to the currently used viral RNA detection tests in patient diagnosis and contact screening algorithms.

Keywords: Antibody; COVID-19; ELISA; IgG; Inactivated virus; SARS-CoV-2.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies, Viral / blood
  • COVID-19 / blood
  • COVID-19 / diagnosis*
  • COVID-19 / pathology
  • COVID-19 Serological Testing / methods*
  • Enzyme-Linked Immunosorbent Assay
  • Humans
  • Immunoglobulin G / blood*
  • Propiolactone / pharmacology*
  • SARS-CoV-2 / immunology*
  • Sensitivity and Specificity
  • Seroepidemiologic Studies
  • Virus Inactivation / drug effects


  • Antibodies, Viral
  • Immunoglobulin G
  • Propiolactone