What would emerge would be a disease as deadly as avian influenza, which currently has a case fatality rate of over 50%, but that moves as easily as seasonal influenza does from person to person,
Bird flu is a disease among animals; it's very difficult for this virus to move from poultry into humans. Our concern is that it will change in a way that will allow it to easily move between humans, and that will trigger a pandemic.
What this virus can't do now is move easily from person to person. We worry that it could develop this characteristic of human-to-human transmission.