Is WHO International Standard for Anti-SARS-CoV-2 Immunoglobulin Clinically Useful?

Background: The introduction of vaccination against SARS-CoV-2 infection needs precise instruments for quality control of vaccination procedure, detection of poor immunological response and estimation of the achieved protection against the disease but also against infection and being infective. Objective: To compare new automated SARS-CoV 2 Ig assay performance characteristics from the automated Elecsys SARS CoV 2 S (Roche) with the new LIAISON SARS-CoV-2 TrimericS IgG (DiaSorin) assay and their compatibility with WHO International Standard for anti-SARS-CoV-2 immunoglobulin. In the context of the mass vaccination programs, we undertook the investigation of clinical utility of the two new automated assays by analyzing results in samples collected at specified time points relative to the vaccination time. Design: Prospective assay evaluation. Patients: Medical staff undergoing vaccination with BioNTech/Pfizer Comirnaty vaccine between January and March 2021 (n = 79) and referred for serum antiSARS-CoV 2 Ig testing prior to vaccination, 21 days after the first dose, and 8, 14 and 30 days after the second dose. Main Outcome Measure(s): Serum antibody levels measured with Roche and DiaSorin assays. Results: Intra-assay imprecision was low with DiaSorin at 3.46%; and Roche at 2.5%. The Passing-Bablok regression equation for all tested samples was y (DiaSorin) = 184.61 + (1.03 x Roche) and the correlation between the assays (r=0.587; p < 0.0001). Conclusions: The novel automated assays exhibit strong concordance in calibration, with assay-specific interpretation required for routine clinical use. These results highlight the need for further work on the international standard of measurement of SARS-CoV 2 Ig especially in era of vaccination. The serological assays can be useful to detect IgG/IgM antibodies, to assess the degree of immunization, to trace the contacts, and to support the decision to readmit people to work or vaccinate them again. However, the values generated by both assays can be markedly different, and assay-specific and personalized interpretation is required.