When we think about virus pathogensis, we tend to get hung up on genetic variation and new “virulent” strains of virus appearing. The recent example of the Sydney 2012 strain of norovirus is a good example of this.
But we also know that around 20% of Europeans are highly resistant to symptomatic infections by noroviruses (Mendelian resistance to human norovirus infections. (2006) Seminars in immunology 18(6): 375-386).
Likewise, host variation in the IL28B gene is responsible for the outcome of hepatitis C virus (HCV) infection (Genetic Variation in the Interleukin-28B Gene Is Associated with Spontaneous Clearance and Progression of Hepatitis C Virus in Moroccan Patients. (2013) PLoS ONE 8(1): e54793).
So when you get sick, make sure you take your fair share of the responsibility!