So the virus..what?

My main goal for the virus was to completely change the composition of the human population over time.  I imagined two main scenarios: completely decimate the current population of healthy people over an extended period of time, or reach a stable composition of the healthy, the sick, and a number of carriers.  

After messing around in my code last week..the results were not at all what I expected. 

No matter what my initial values for each parameter, the population would continuously be overrun by completely healthy people in a matter of weeks after the initial infections.