False positivity of SARS-CoV-2 IgG/total antibody tests in ten out of 100 archived sera collected in the summer 2018 and winter 2018/2019. A signal (S)/cut-off (CO) value ≥1 is considered as positive for SARS-CoV-2 IgG/total antibodies. Results of the ViraChip® IgG test (Viramed, VM), of the plaque reduction neutralization assay (PRNT, Figure S1), and of both recomLine assays (blot v1 and v2) are listed in the table. p, positive and n, negative. For better clarity, positive test results are printed in red in the table.