Hepatitis C virus (HCV) has the propensity to cause chronic infection. HCV affects an estimated 170 million people worldwide. Immune escape by continuous genetic diversification is commonly described using a metaphor of "arm race" between virus and host. We developed a mathematical model that explained all clinical observations which could not be explained by the "arm race theory". The model applied to network of cross-immunoreactivity suggests antigenic cooperation as a mechanism of mitigating the immune pressure on HCV variants. Cross-immunoreactivity was observed for dengue, influenza, etc. Therefore antigenic cooperation is a new target for therapeutic- and vaccine- development strategies. Joint work with P.Skums and Yu. Khudyakov (CDC)