These are a set of 4 online simulations.  You can choose whether to focus on a single class, or see what happens between two classes, when a disease is introduced.  Counter-Plague Plus versions allow you to designate a number of people who are already immune to the disease.

To start, decide how many people you want in the class(es), and how many people are initially infected by the disease.  Then press Next to see what happens step by step, or Run for the complete epidemic.  A bar chart on the bottom right of the screen records the number of cases at each step, and how many people recover. 

The rules are as for Counter Plague, so dice determine whether the infection is passed on or not. You can change the number of infections which each die number on the die produces. In e-Counter Plague 2 class versions, you can set different infection rates for the class which has the initial infection and the other class.

Green smiley faces are people who have not yet had the disease.  Red miserable faces are people who are sick.  Blue faces are people who have recovered and are now immune or have been immunised (in e-Counter Plague Plus versions).