Figure 1.

Virus isolation. Nasopharyngeal swabs positive for COVID-19 with cT value of <20.0 in qRT-PCR were considered for virus isolation in Vero cells. The samples were filtered in a 0.45-µm syringe filter, and 500 µl of the filtrate was used to infect Vero cells. Samples that produced CPE within three successive passages in Vero cells were authenticated and accessioned. Characteristics of the CPE produced by WT and Delta (A) variant of SARS-CoV-2 at passage level 5 is shown. Plaque morphology of WT and Delta variant of SARS-CoV-2 is also shown (B).