Fig. 2. Seroconversion of ferrets. Ferrets were tested for seroconversion at 19 and 21 days p.i. using a blocking ELISA detecting antibodies against the NP gene. In the H3N2 AT group, one of the animals died before seroconversion and hence only one animal is above the baseline. Serum samples were tested in duplicate and values are presented as mean±sem per cent seropositive.