Evaluation of the IgG antibody response to SARS CoV-2 infection and performance of a lateral flow immunoassay: cross-sectional and longitudinal analysis over 11 months

Louise Robertson, Julie Moore, Kevin Blighe, Kok Yew Ng, Nigel Quinn, Fergal Jennings, Gary Warnock, Peter Sharpe, Mark Clarke, Kathryn Maguire, Sharon Rainey, RK Price, William Burns, Amanda Kowalczyk, Agnes Awuah, Sara Mc Namee, Gayle Wallace, David Hunter, Steve Sager, Connie Chao-ShernM. Andrew Nesbit, James McLaughlin, Tara C. B. Moore

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Objective To evaluate the dynamics and longevity of the humoral immune response to SARS-CoV-2 infection and assess the performance of professional use of the UK-RTC AbC-19 Rapid Test lateral flow immunoassay (LFIA) for the target condition of SARS-CoV-2 spike protein IgG antibodies.

Design Nationwide serological study.

Setting Northern Ireland, UK, May 2020–February 2021.

Participants Plasma samples were collected from a diverse cohort of individuals from the general public (n=279), Northern Ireland healthcare workers (n=195), pre-pandemic blood donations and research studies (n=223) and through a convalescent plasma programme (n=183). Plasma donors (n=101) were followed with sequential samples over 11 months post-symptom onset.

Main outcome measures SARS-CoV-2 antibody levels in plasma samples using Roche Elecsys Anti-SARS-CoV-2 IgG/IgA/IgM, Abbott SARS-CoV-2 IgG and EuroImmun IgG SARS-CoV-2 ELISA immunoassays over time. UK-RTC AbC-19 LFIA sensitivity and specificity, estimated using a three-reference standard system to establish a characterised panel of 330 positive and 488 negative SARS-CoV-2 IgG samples.

Results We detected persistence of SARS-CoV-2 IgG antibodies for up to 10 months post-infection, across a minimum of two laboratory immunoassays. On the known positive cohort, the UK-RTC AbC-19 LFIA showed a sensitivity of 97.58% (95.28% to 98.95%) and on known negatives, showed specificity of 99.59% (98.53 % to 99.95%).

Conclusions Through comprehensive analysis of a cohort of pre-pandemic and pandemic individuals, we show detectable levels of IgG antibodies, lasting over 46 weeks when assessed by EuroImmun ELISA, providing insight to antibody levels at later time points post-infection. We show good laboratory validation performance metrics for the AbC-19 rapid test for SARS-CoV-2 spike protein IgG antibody detection in a laboratory-based setting.
Original languageEnglish
JournalBMJ Open
Issue number6
Early online date29 Jun 2021
Publication statusPublished online - 29 Jun 2021

Bibliographical note

Publisher Copyright:
© Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.


  • Antibodies, Viral
  • Antibody Formation
  • COVID-19
  • Covid-19
  • Cross-Sectional Studies
  • Diagnostic Microbiology
  • Humans
  • Immunization, Passive
  • Immunoassay
  • Immunoglobulin G
  • Molecular Diagnostics
  • Northern Ireland
  • SARS-CoV-2
  • Sensitivity and Specificity
  • Spike Glycoprotein, Coronavirus
  • molecular diagnostics
  • diagnostic microbiology


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