Anti-Spike protein assays to determine post-vaccination antibody levels: a head-to-head comparison of five quantitative assays

Abstract

Background Reliable quantification of the antibody response to SARS-CoV-2 vaccination is highly relevant for identifying possible vaccine failure and estimating the time of protection. Therefore, we aimed to evaluate the performance of five different Anti-SARS-CoV-2 antibody assays regarding the quantification of anti-spike (S) antibodies induced after a single dose of BNT162b2. Methods Sera of n=69 SARS-CoV-2 naive individuals 21+/-1 days after vaccination with BNT162b2 (Pfizer/BioNTech) were tested using the following quantitative SARS-CoV-2 antibody assays: Roche S total antibody, DiaSorin trimeric spike IgG, DiaSorin S1/S2 IgG, Abbott II IgG, and Serion/Virion IgG. Test agreement was assessed by Passing-Bablok regression. Results were further compared to the percent inhibition calculated from a surrogate virus neutralization test (sVNT) by correlation and ROC (receiver-operating-characteristics) analysis. Results Individual values were distributed over several orders of magnitude for all assays evaluated. Although the assays were in good overall agreement (rho=0.80-0.94), Passing-Bablok regression revealed systematic and proportional differences, which could not be eliminated by converting the results to BAU/mL as suggested by the manufacturers. 7 (10%) individuals had a negative sVNT results (i.e. <30% inhibition). These samples were reliably identified by most assays and yielded low binding antibody levels (ROC-AUCs 0.84-0.93). Conclusions Although all assays evaluated showed good correlation, readings from different assays were not interchangeable, even when converted to BAU/mL using the WHO international standard for SARS-CoV-2 immunoglobulin. This highlights the need for further standardization of SARS-CoV-2 serology.

Usefulness of IVD Kits for the Assessment of SARS-CoV-2 Antibodies to Evaluate the Humoral Response to Vaccination

“…Some initial studies used only the ELISA method [ 27 ]. A publication on a similar topic to our study includes another paper by Perkmann et al [ 28 ] who compared five tests (including three that were evaluated in our study) using sera from 69 individuals who did not suffer from SARS-CoV-2 infection. The samples used were obtained 21 days after the first dose of the BNT162b2 vaccine.…”

Initial SARS-CoV-2 vaccination response can predict booster response for BNT162b2 but not for AZD1222

“…All analyses were performed at the Department of Laboratory Medicine, Medical University of Vienna, which operates a certified (ISO 9001:2015) and accredited (ISO 15189:2012) quality management system. Performance data of both tests have been published before ( Perkmann et al, 2020 , Perkmann et al, 2021a ).…”

“…Determination of spike-protein specific antibodies after SARS-CoV-2 vaccination, although not unrestrictedly recommended ( Centers for Disease Control and Prevention, 2021 ), is commonly performed. The post-vaccination antibody levels, even when measured with standardized commercially available CE-certified quantitative test systems, differ significantly ( Kristiansen et al, 2021 , Perkmann et al, 2021a ). Furthermore, in addition to these analytically related differences, there are significant differences in expected levels depending on the age and serostatus of the vaccinees ( Krammer et al, 2021 , Perkmann et al, 2021b , Subbarao et al, 2021 ), the vaccine used ( Eyre et al, 2021 ), and the timing of blood collection (elapsed time interval since first or second dose).…”

Immunogenicity of SARS-CoV-2 BNT162b2 vaccine in solid organ transplant recipients

“…Anti-SARS-CoV-2 RBD IgG assays have shown an excellent correlation with neutralizing antibodies. 3 Antibodies were measured at a median of 10 (IQR: 9-10) days from the second vaccination dose. We evaluated the associations among demographic and clinical characteristics and positive antibody response using modified Poisson regression with a robust variance estimator.…”