Reassortants of influenza B viruses for use in vaccines: an evaluation.

Three slightly different procedures for the preparation of influenza B virus reassortants from B/Lee/40 and B/Lyon/79, and B/Johannesburg/58 and B/Hong Kong/82 parental viruses are described. Following cloning procedures in eggs or allantois-on-shell cultures in the presence of antisera to B/Lee or B/Johannesburg, twenty-eight putative reassortants were obtained. Using SDS-PAGE to determine the migration rates of virion polypeptides, eighteen isolates from mixed infections of B/Lee with B/Lyon, and three isolates from mixed infections of B/Johannesburg with B/Hong Kong, were found to be reassortants. All reassortants possessed surface proteins derived from either B/Lyon or B/Hong Kong and one to three internal polypeptides from either B/Lee or B/Johannesburg. None of the reassortants showed a growth capacity in embryonated eggs as high as that of their B/Lee or B/Johannesburg parent viruses. The procedures used, and the influenza B reassortants thus generated, would appear to offer no major advantages over the existing methods and influenza B strains at present employed for the preparation of inactivated influenza virus vaccines.