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Overview of sample origin. A total of 334 samples were tested. A commercial IgG ELISA (Euroimmun, Lübeck, Germany) was used for pre-screening. All but 30 samples were positive for SARS-CoV-2 IgG antibodies, of which 128 came from patients who had recently recovered from confirmed COVID-19 and 177 were from vaccinated individuals (collected at least three weeks after vaccination). In addition, 30 samples collected in mid to late 2018 served as negative control samples.
