Biological, genetic and biochemical characterization of a cold-adapted recombinant A/Victoria/3/75 virus and its evaluation in volunteers.

A recombinant virus AA-CR19 was produced that contains RNA segments coding for one polymerase protein, the nucleoprotein and the matrix protein of cold-adapted A/Ann Arbor/6/60, but HA, NA and two other genes coding for polymerase proteins from A/Victoria/3/75. The nonstructural protein gene is probably derived from A/Ann Arbor/6/60, but may contain a spontaneous mutation. Biological characterization of AA-CR19 showed that it possesses the gene(s) responsible for cold-adaptation and temperature-sensitivity of the A/Ann Arbor/6/60 parent. At a dose of 10(7.2) TCID/50. AA-CR19 was found to be immunogenic and attenuated for seronegative volunteers.