The Sofia SARS Antigen FIA product insert indicates a LOD of 2.26x10 2 TCID50/mL 9 of BEI product number NR-52286. The product insert claims that the starting concentration of the NR-52286 lot used had a TCID50 of 3.4 x 10 5 per mL. To determine the copies per mL of this lot, we consulted the BEI reference data sheets, however no lot is shown with this starting concentration, and personal communication with BEI confirmed no such lot was made. For the three lots of NR-52286 with certificates of analysis as of August 8, 2020, the copies per mL per TCID50 per mL ranges from 1106 to 7250. Therefore, we assume the LOD for the Sofia test in terms of copies per mL is between 2.5x10 5 and 1.6x10 6 copies per mL.