I rarely get sick. The original mutated viruses were carrier viruses for cancer and the common cold, and I'm up-to-date on my vaccinations.
Also, amplification happens in a very short time frame. If you don't trust me, just lock me somewhere for 12 hours. If I'm still me, not zombifying.
I couldn't really blame them. If more people shot just in case, there would have been fewer dead and taken cities in the Rising. Not that I want to be shot, but it's an understandable reaction, as I told Thomas.