Detection of PB2 627K mutation in two highly pathogenic isolates of the H7N9 subtype influenza A virus from chickens in northern China

PB2 E627K mutation of influenza A virus has been considered relevant to increased mammalian virulence and adaptation. In H7N9, the substitution is naturally confined to most human isolates and few low pathogenic avian isolates. However, we isolated two highly pathogenic H7N9 variants harboring PB2 627K from chickens in northern China.