Some time ago I suggested that Prime Base was the victim of a contaminated batch of Smallpox Vaccine. There was some discussion of whether or not the Project would have detected the contamination (I had suggested a prion) and whether prions would even have been available in the late 1980s.
I have been looking for the Quality Assurance protocols for the vaccine and my wonderful, brilliant wife found this
http://www.fda.gov/downloads/Biologi.../UCM078071.pdf. It is from 2002. It gives a clear indication that the testing that would have been done in the 1980s is pretty limited "Testing for anaerobes, coliforms,hemolytic streptococci and coagulasepositive
staphylococci, viable bacteria"
So I am going to back off the prions and instead suggest that the vaccine was purposefully contaminated with the rabies virus. None of the listed tests would have detected it. Rabies has a incubation period of 2 to 12 weeks. with as short as four days being possible. The disease can be treated post exposure if the rabies vaccine is given promptly enough, generally within ten days of exposure. Krell would have contaminated the smallpox vaccine with a strain of rabies that has a latency period that ensures few victims would show symptoms in time for the base to determine what was happening. Rabies is nearly 100% fatal if the post exposure treatment isn't given in the window, and before 2004 appears to have been invariably fatal.