CPSF4 and infection: Surprisingly, earlier studies have shown that the F103L and M106I mutations found in the first fatal H5N1human infection in 1997 [81], resulted in a loss of ability of NS1 to bind CPSF30 and inhibit host gene expression [82] as has also been reported for A/PR/8/34 (H1N1) [83]and pandemic 2009 H1N1 viruses [84].