Why are infections so freaking lethal?

[Shurp]

Customize scenario, modify stat, immunity gain %200. Diseases are still deadly but not getting your doctor onto the patient THE MOMENT they develop a disease isn't a death sentance

You can modify immunity gain right from the scenario window, without applying a mod?  Clever!  But only works on a new game.  I'll have to try that next game.

[AngleWyrm]

Mortality rate
Mortality rate is a measure of the time until 1/2 of the infected population die. A mortality rate of 3 weeks means that 1/2 of the people who have had the disease for three weeks are dead.

It is also possible to express mortality as a variable against a standard unit of time, such as 6 months. A mortality of 3/4 at three months then means that 3 months after infection 3/4 of the infected die.