The CDC scientists also reported that the virus is missing a feature in an internal gene called PB2 that is known to relate to transmissibility.

All seasonal flu viruses and the past three pandemic viruses -- in other words, all flu viruses which have successfully made the jump from other species into humans -- have had this feature. The H1N1 virus does not.

They don't know how the virus achieved transmissibility without this mutation or how likely it is to acquire it. But Tumpey said the mutation is also linked to increased virulence or disease severity and the flu community is watching closely for this change.



Ok, so without this gene this flu should not exist. It contains swine, bird and human strains without the gene that would have allowed it to jump species. How? it has to be tailor made for humans!