Single-step growth curves of C-PA and WSN in infected cells. MDCK (A) and Vero (B) cells were infected with C-PA or WSN at an MOI of 5. Viruses were harvested 2, 4, 6, 8, 10, and 12 hr after infection and their titers on MDCK cells measured by a plaque-formation assay. The mean and standard deviation (error bar in the graph) of each plaque titer were calculated from 3 independent experiments. Statistical significance was evaluated with Student’s t-test. *p < 0.05, ***p < 0.005.