HS Lessons On Modeling Virus Spread
Here are two resources that might be appropriate, but neither is a spreadsheet model. 

The first is a resource called Contagion that has just been created for the Greenfoot Java system (IDE plus resources). You can find it at the Greenroom. 

The second is a section on Simulation in a book called Polymorphism Companion. The book is actually the second volume of a pair and you might need the first one also Polymorphism: As It Is Played. They are both about using polymorphism, especially in Java. 

Both of these resources model a disease spreading through a population. They have various parameters you can set to get some realistic(ish) results. Think of a Disease interface, for example, with diseases of various characteristics implemented via polymorphism.