InfluenzaFollowing the identification of a virus agent causing human influenza,314 efforts were made to develop vaccines effective in preventing or at least mitigating the infection. The finding of Burnet315 that the fertile hen's egg provided a favorable medium for cultivating the influenza virus led ultimately to the use of this agent as the preferred culture medium. The demonstration that at least two distinct types of virus — designated "A" and "B" — could cause influenza316,317 posed the necessity of producing an effective bivalent vaccine. Numerous studies, usually with monovalent preparations, gave more or less equivocal results, whether the vaccine . . .