Hybrid Formation of Influenza Virus at 25

Abstract

It is clear that “cold hybrids” of influenza virus can be obtained at 25° by recombination of two live influenza virus, of human and animal origins, one of which is cold-adapted. The presently described “cold hybrids” contain the hemagglutinin of the current human or equine strains and the neuraminidase of the established “cold variant”. These derived lines can grow at 25° in tissue culture and embryonated eggs and are also able to form plaques at 25°. They can grow in mouse lungs and are temperature sensitive. The Hong Kong “cold hybrid” (CHI) is attenuated for animals and highly immunogenic. Since only about four weeks were required to obtain these strains, it is evident that the procedures used offer potential practical advantages for production of live influenza vaccine strains.