Question: if say 2 people had the same illness but only one survived,is this because even if it is the same virus it is slightly different so they cant cure every person with the same disease?

Hayley Evers-King answered on 13 Mar 2013:

Usually this happens because different people have different reactions to a virus or disease. This can come from their previous health (maybe they are old/young or have been sick recently) or their genetics. Some people are more resistent to viruses and diseases than others, by studying this, scientists can figure out how to treat different diseases.

However, as you say, viruses can also change and be slightly different – flu is a good example of this.