Laboratory evaluation of SARS-CoV-2 antibodies: detectable IgG up to 20 weeks post infection

Abstract Background The SARS-CoV-2 pandemic necessitated rapid and global responses across all areas of healthcare, including an unprecedented interest in serological immunoassays to detect antibodies to the virus. The dynamics of the immune response to SARS-CoV-2 is still not well understood and requires further investigation into the longevity of humoral immune response that is evoked due to SARS-CoV-2 infection. Methods We measured SARS-CoV-2 antibody levels in plasma samples from 880 people in Northern Ireland using Roche Elecsys Anti-SARS-CoV-2 IgG/IgA/IgM, Abbott SARS-CoV-2 IgG and EuroImmun IgG SARS-CoV-2 ELISA immunoassays to analyse immune dynamics over time. We undertook a laboratory evaluation for the UK-RTC AbC-19 rapid lateral flow immunoassay (LFIA), for the target condition of SARS-CoV-2 Spike protein IgG antibodies using a 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 up to 140 days (20 weeks) post infection, across all three laboratory-controlled immunoassays. On the known positive cohort, the UK-RTC AbC-19 lateral flow immunoassay showed a sensitivity of 97.58% (95.28%-98.95%) and on known negatives, showed specificity of 99.59% (98.53 %-99.95%). Conclusions Through comprehensive analysis of a cohort of pre-pandemic and pandemic individuals, we show detectable levels of IgG antibodies, lasting up to 140 days, 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.