The next step was to engineer the H5 gene into the vaccine. It was inserted into segment 8, where the NS2 gene had been.
Another aspect of the new vaccine's design makes it safer still, by rendering successful reassortment less likely. Both NS1 and NS2 are needed for viral replication. Since the two genes are now separated into different segments, any reassortment will have to include both segments, instead of just segment 8, in order for a reassortant virus to be viable. This greatly reduced the probability of successful reassortment.
The World Health Organization (WHO) recognizes avian influenza subtypes H5, H7, and H9 as potential pandemic viruses, because they all have in rare instances infected humans, and because they circulate in wild birds. Single reassortants could be sufficient to breach the species barrier, and since they do not circulate among us, we lack any immunity. Moreover, H5 is unusually lethal, having killed roughly half of those few it is confirmed to have infected.
|Contact: Garth Hogan|
American Society for Microbiology