F2 and influenza: Considering that the PB1-F2 ORF from 20Ch557/H6N2 virus is 90 amino acids in length – as commonly found in AIV isolated from ducks – and that the all PB1-F2 proteins from AIV from SAm lineage have phenylalanine at position 83 instead of serine, further functional analyses of the PB1-F2 protein from 20Ch557/H6N2 virus should be considered to determine its role in influenza pathogenicity in chickens.