Figure 1.

Schematic diagrams showing the two experimental procedures used to investigate the antiviral effect of povidone-iodine (PVP-I) against severe acute respiratory syndrome-coronavirus-2 (SARS-CoV2) in vitro: (a) stock virus (3 μl, 10⁶ IU/ml) was mixed with 3 μl PVP-I solution (2, 1, 0.5, 0.25, 0.125, 0.0625 mg/ml) in test tubes. Contact times of 30 s, 1 min, 2 min and 5 min were used for each concentration. Each mixture was then diluted 500-fold with 3 ml culture medium and 500 μl aliquots of the diluted solutions were added to wells containing Vero cells (three replicates for each solution). After incubating at 35°C under 5% CO₂ for 48 h, the cytopathic effect was observed under a microscope; (b) virus solution (0.5 ml) was mixed with different concentrations of PVP-I (2, 1, 0.5, 0.25, 0.125, 0.0625 mg/ml) for 1 min. The mixture was transferred to an ultrafiltration centrifuge tube, centrifuged at 485.63 g for 5 min, and then 1 ml of culture medium was added to resuspend the mixture. Subsequently, 6 μl of 1 ml mixture was diluted 1:500 with 3 ml culture medium and 500 μl of diluted solutions was added to the wells (three replicates for each solution). All plates were incubated at 35°C under 5% CO₂ for 48 h. The 50% tissue culture infectious dose assay values were used to determine virus titre using the method of Reed and Muench. ¹⁹