Thirty-seven samples taken from patients with a PCR-confirmed SARS-CoV-2 infection were analyzed with eight SARS-CoV-2 IgG or total antibody assays. Samples #1, #7, and #9 were taken nine days before to four days after PCR and were all found to be free of SARS-CoV-2 antibodies by the assays. These samples were not considered for calculation of the sensitivity but demonstrated seroconversion (Figure 1). Out of the remaining 34 samples, only one serum (#20; Figure 1), which was obtained from patient no. 12 ten days after a positive RT-PCR, tested negative for SARS-CoV-2 IgG/total antibodies in the eight assays. However, this sample exhibited a PRNT 1:10–1:20. All other samples were reactive in at least one assay (Figure 1). Twenty (76.9%) patients developed virus-neutralizing antibodies, as shown by a PRNT >1:10 (Figure 1 and Figure S1). With respect to the SARS-CoV-2 PCR (reference 1) or the PRNT results (reference 2), assay sensitivities ranged from 80.8% to 96.3% (Table 1).