(A-B) Supernatants from the panel of infected (A) Vero E6-TMPRSS2 and (B) Vero E6 cells were harvested when CPE was observed and the viral titer (FFU/mL measured by focus forming assay) was determined for the final time point of each sample that successfully isolated. Samples are colored according to the day CPE was observed and the sample was harvested. Total E RNA CT of the original clinical sample used for viral isolation is plotted on the X axis. Data shown is from the subset of samples that successfully isolated in each cell line. Limit of detection for infectious titer is 400 FFU/mL. 