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Figure. A) The 8-plasmid reverse genetics system to generate recombinant,
live, attenuated pandemic influenza vaccines. Six plasmids encoding the
internal genes of the attenuated donor virus are mixed with 2 plasmids
encoding the circulating avian virus hemagglutinin (HA) and neuraminidase
(NA) genes (which may or may not have been modified to remove virulence
motifs). Qualified cells are transfected with the plasmids, and the attenuated
reassortant virus is isolated. B). Generation of live, attenuated pandemic
influenza vaccine viruses with the 6 internal genes from the attenuated
donor virus bearing attenuating mutations (*) and the HA and NA genes
from the circulating avian virus by classic reassortment. The 6-2 reassortants
generated by this method are selected in the presence of antiserum specific
for HA and NA of the attenuated donor virus.
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