Antigenic escape (alternatively called immune escape, immune evasion or escape mutation) occurs when the immune system of a host, especially of a human being, is unable to respond to an infectious agent, or, in other words, the host's immune system is no longer able to recognize and eliminate a pathogen such as a virus. This process can occur in a number of different ways of both a genetic and an environmental nature. Such mechanisms include homologous recombination, and manipulation and resistance of the host's immune responses.