The symptoms that the survivors are experiencing are very much like the symptoms of Gulf War Syndrome. See this FR post. I wonder if the anthrax powder has been tested for chemical weapons in addition to anthrax, perhaps the cholinesterase inhibitors that are suspected of causing Gulf War Syndrome.
Leaving us to ask another question. Is the genie getting out of the bottle all by itself, if prematurely? Or is this merely Phase II of a "timed release" program, designed to reach a climax...when?