Impact of the elderberry extract on propagation of IV. A) Focus size reduction assay. MDCK cells were infected with the two virus strains as indicated and incubated for 48 h in the presence of the extract (1:100). Foci were detected by immunochemistry. B) Pre-treated MDCK cells were infected with pre-treated virus and were propagated for 48 h in the presence of the extract. As control untreated virus and cells were used for infection. The mean titre of three independent experiments is given as percentage of the control (black) set to 100%. Standard deviation is indicated (KAN-1: p < 0.07, Mass: p < 0.03).