Antibody levels were determined by the Roche Elecsys SARS-CoV-2 S assay in arbitrary units (AU) per ml as described previously [9 (link)] with a linear range from 0.4 AU/mL to 25,000 AU/mL. Samples that exceeded 25,000 AU/mL were manually diluted at 1:30 and retested. A negative test result was defined as <0.8 AU/mL, a low positive response between 0.8 AU/mL and 103 AU/mL, and a positive response >103 AU/mL. SARS-CoV-2 Nucleocapsid antibodies were assessed by the Elecsys anti-NC-SARS-CoV-2 Ig assay (Roche, Mannheim Germany; cutoff ≥ 1 COI/mL).
Cellular immune response was determined by a commercial spike-specific Interferon-Gamma-Release-Assay (IGRA, EUROIMMUN, Lübeck, Germany), as previously described [9 (link)]. The IGRA was interpreted according to the manufacturer’s instructions, with Interferon-gamma (IFN-γ) levels of <100 mlU/mL being negative, 100–200 mlU/mL being low positive, and >200 mlU/mL being high-positive [30 (link)].
Cellular immune response was determined by a commercial spike-specific Interferon-Gamma-Release-Assay (IGRA, EUROIMMUN, Lübeck, Germany), as previously described [9 (link)]. The IGRA was interpreted according to the manufacturer’s instructions, with Interferon-gamma (IFN-γ) levels of <100 mlU/mL being negative, 100–200 mlU/mL being low positive, and >200 mlU/mL being high-positive [30 (link)].
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