When are the humans alerted?

[AnimalMan]

Severity gives cure away. The more severe it is the more the WHO wants to cure it i.e severity = danger to society. Play parasite and use symbiosis you'll understand a little better

- oh and brutal and mega brutal random blood tests take place limiting the range of secrecy that can be obtained using low severity tactics. Usually by the time you have a single country fully infected you will get a blood test.