Influenza — The Problems and the Future

The major problem concerning the control of influenza A is that of anticipating future antigenic changes. “Newcomer” viruses associated with pandemics appear to arise either from genetic recombination between human and animal viruses or from reactivation of a former epidemic human virus latent over long periods of time. Minor antigenic changes are due to the selection of variant strains by passage through a partly immune population. Immunity is largely dependent on serum antibodies, but previous infection appears to modify the response to a strain with an unrelated hæmagglutinin. A shared neuraminidase antigen may explain such heterologous immunity. Local (nasal) antibodies strengthen immunity by adding a component to serum antibodies. Inactivated vaccine given intranasally produces a local and serum antibody response which is unpredictable and therefore variable in degree. Vaccines made from live attenuated viruses probably have a place in immunization different from that of inactivated vaccines. They should be more effective when the population has had little previous contact with the current virus than at other times. Doubt is expressed that vaccines will ever provide epidemic control of influenza.