pathogens such as the influenza virus have receptors that enable them to bind to host cell surfaces antibodies to these viral receptors prevent the virus from binding to and infecting cells these are neutralizing antibodies since they neutralize the ability of the virus to infect the cell in some cases viruses arise that are able to escape the effects of neutralizing antibodies this can happen when two different strains of influenza virus are able to infect the same host cell the progeny viruses produced from such doubly infected cells can contain segments of genome from either of the two original viruses some viruses will acquire a segment of genome from the other strain encoding the receptor for host cell surfaces neutralizing antibodies that block the binding of the original virus will be unable to recognize the receptor from the second strain and will be unable to prevent the virus binding to and infecting host cells this process in which large changes in the antigenicity of the virus occur is known as antigenic shift these large changes can mean that much of the immunity against the original virus is ineffective and such antigenic shift mutations are often associated with large-scale virus epidemics