Attenuation of influenza A/New Jersey/76 virus strain, preparation of live vaccine and vaccine reactogenicity in volunteers.

The NIB-3 strain (a recombinant of influenza A/New Jersey/76 and X-31 strains) was further attenuated by nine egg passages at 28 degrees C for the purpose of obtaining a "cold-adapted variant" suitable for preparation of live freeze-dried vaccine with 5% peptone. The vaccine with two infectivity titres, of 7 and 6 log EID50/dose respectively, administered intranasally, was studied in a double-blind placebo-controlled field trial. The reactogenicity of the vaccine was evaluated on the basis of fever reactions during the first three days after vaccination and by the detection of local virus recovery from throat swabs taken on the first four days after vaccination.