Fig. 4: Antibody responses in donor and recipient ferrets.

Sera were collected from donor and recipient ferrets on the indicated days. Antibody responses against A/H1N1 virus (a) were measured by hemagglutination inhibition (HI) assay, whereas responses against SARS-CoV-2 (b) and SARS-CoV (c) were assessed using a nucleoprotein (NP) ELISA. Dotted lines indicate the detection limit of each assay. OD: Optic density.