(a) A time of addition assay was conducted, in which 2.5 mg/mL of Spirulina extract was added at the indicated timepoints to MDCK cells infected with the A/WSN/33(H1N1) influenza strain. E0 medium was overlaid on cultures at 9 hours post-infection, and supernatants were harvested at 12 hours post-infection. (b) Virus yields were determined by the plaque assay, and reported as a percentage of untreated controls. Data represent the mean ± SD for two independent experiments. Statistical analysis was performed with two-tailed unpaired t-test, and the statistical significance was determined to be *P ≤ 0.05, **P ≤ 0.01, or ***P ≤ 0.001 for each treated group versus the virus control.