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H5N1 Recombination and Reassortment
November 25, 2004
>>"In such a situation, the risk of genetic reassortment which might arise from co-infection of human and avian influenza virus, resulting in a new influenza virus with a pandemic potential, has become a major common concern," he noted. <<
WHO has the right idea, but the wrong mechanism. The human receptor binding domain is on the H. Thus, if the same cell was infected with H3N2 and H5N1, the human H3 could be swapped for the avian H5 to produce H3N1. This reassorted virus would be able to be transmistted from human to human, but most humans have antibodies to H3 (from H3N2 infections or vaccines), so there wouldn't be much of a pandemic.
However, if the receptor binding domain on H3 was put on the avian H5 via recombination, then the H5N1 would be able to transmit human to human, but would still be largely H5N1, the virus that produces a 70-80% case fatality rate in Vietnam and Thailand.
Such a recombinant, capable of infecting 1/4 of the world's population and killing 70% of those infected, would kill over 1 BILLION, not the 2-7 million cited by WHO.
Reassortment happens all of the time, but there is no documented human H3N1 because recombination drives influenza emergence and evolution, not reassortment (although reassortment magnifies recombination).