LABORATORY PROPERTIES OF COLD-ADAPTED INFLUENZA-B LIVE VACCINE STRAINS DEVELOPED IN THE UNITED-STATES AND USSR, AND THEIR B/ANN-ARBOR/1/86 COLD-ADAPTED REASSORTANT VACCINE CANDIDATES

The adaptation of two influenza B strains (B/Leningrad/14/55 and B/Ann Arbor/1/66) to replication at 25°C is described. Comparison of the two viruses indicates that both also exhibit temperature sensitive phenotypes, although that of the virus B/Leningrad/14/55 is less pronounced. When inoculated into ferrets both viruses replicate well in the trachea, but only the B/Leningrad/14/55 cold-adapted virus replicates in the lungs. This virus exhibited a moderate level of attenuation in the animals, in contrast to the B/Ann Arbor/1/66 cold-adapted virus, which was fully attenuated. Reassortant viruses deriving the surface antigens of the contemporary wild type virus B/Ann Arbor/1/86 and most or all of their other genes, from one or other cold-adapted parent, were virtually indistinguishable from their respective cold-adapted parents. The B/Leningrad/14/55 reassortant was slightly more attenuated than its cold-adapted parent in ferrets. These studies extend knowledge of the properties of viruses used to prepare experimental live influenza B human vaccines. © 1990.