[Influenza].

Progress in influenza research within the last 5 years with particular reference to the variation of surface antigens and its relation to epidemiology and immunity is reviewed. Antigenic shift may be a consequence of reassortment of genes between influenza strains. The origin of the newly introduced genes cannot be ascertained at present. The possibility that under certain circumstances animal strains become established in the human population with or without genetic interaction with human strains has to be considered and even latency of the virus in men is within the realms of possibility. The monoclonal antibody technique revealed much more complicated antigenic structures of the hemagglutinin than has been proposed before and at present a forecast of future antigenic changes is impossible. Furthermore, no future epidemiologic developments can be predicted from the antigenic changes alone.