Figure 1

For the development and characterization of suitable EQA sample material, a dilution series of SARS-CoV-2 cell culture supernatants and a SARS-CoV-2 negative sample were measured by antigen LFTs (a, b) and automated immunoassays (c) by four expert laboratories and the manufacturer. Test line intensities were interpreted in comparison to the respective control line intensity and are shown for (a) lyophilized sample material and (b) for liquid sample material. Applied grading system: ‘test line stronger than control line (5), ‘test line as strong as control line’ (4), ‘test line weaker than control line’ (3), ‘test line much weaker than control line’ (2) and ‘test line faint, just visible’ (1), a negative result was defined as (0). Results from automated immunoassays are also compared for lyophilized and liquid sample material (c). The different tests used are shown in different colours. The LFTs of Abbott—Panbio COVID-19 Ag Rapid Test (light blue) and Roche (SD Biosensor) 1—SARS-CoV-2 Rapid Ag Test (light green) were used by several laboratories. Automated immunoassays were applied by two laboratories with either the SARS-CoV-2 Ag Roche Cobas [COI] or the SARS-CoV-2 Ag-CLIA Diasorin [TCID₅₀/mL].