In order to examine the likelihood of efficient airborne human-to-human transmission of the 2012 H7N3 viruses, wildtype and mutant residues at previously identified key positions making H5 viruses transmissable in ferrets[33, 35] were compared to the corresponding residues in the hemagglutinin amino acid sequence for H7N3. Listed residue positions are based on H3 numbering as used in Imai et al. followed by alternative numbering as in Herfst et al. in parenthesis. An asterisk * indicates the single position where the new strain has a mammalian transmission-adapted rather than the avian wildtype residue.