Vaccination infection idea

After some initial testing that just allowing contagious patients to infect other patient who have the same disease does not produce enough infected people to make a decent epidemic. The idea now is to let contagious patients change the disease of another patient as long as that patient is not fully diagnosed yet and, to begin with, has a non-visual disease (of which most contagious diseases are to make it simple to spread without changing the player model).

I was thinking about how to implement it and came up with a basic outline.

• For patients with the same disease infections work as they currently do where the contagious strain is simply passed on making the infected patient now contagious as well.
• For patient with a different disease (non-visual) who is not diagnosed, when infected:
  1. Change the patients disease to the contagious disease - set the infected icon, let them infect others etc.
  2. Allow them to continue to the GP or next diagnostic step (no patient would suddenly notice they had a different disease and turn around spontaneously)
  3. The member of staff in the next room they visit "realises" that they have a different disease than they were supposed visit the room for and sends them back to the GP.
  4. GP is confused about the patients diagnosis and resets the percentage diagnosed back to 0 - this could potential make the length of diagnosis up to 2x as long depending on how far they are through diagnosis and is something which could be amended for difficulty.
  5. The patient continues the game as a patient with the contagious disease through diagnosis, treatment etc. and acts like a contagious patient infecting others in a similar way.

Ideas, improvements, or limitations of this idea i'd like to hear about then hopefully we'll have something resembling the original epidemics.