Antiviral activity of fucoidan against NDV (PFU reduction). Vero cells (1.5 × 105 cells) plated in 24-well plates were infected with NDV and treated with different concentrations of fucoidan or ribavirin during and after infection for 48 h, and the antiviral activity was determined in a PFU reduction assay. The data are expressed as relative PFU (%) to that for the untreated virus-infected control cells, which was defined as 100%. VC, viral control. The data shown are the mean ± SD from four replicated experiments.