Experiments in the preparation of live influenza B vaccines.

A study is described of the selection of influenza B virus recombinants. Three virulent viruses isolated in 1970, 1970 and 1973, were crossed with host-range mutants of low virulence for man, which had originally been isolated in 1940, 1959 and 1956, respectively. Nine presumptive recombinants were inoculated into volunteers with low initial HI antibody titres. Although a number proved attenuated and there was evidence of high frequency of recombination, antigenic characterization of neuraminidases proved difficult. There was always some crossing between parental surface antigens, and appropriate antigenic hybrids for preparation of reference antisera were not available. Comparative virus titres at 33 degrees C and 38 degrees C were of limited value as a genetic marker. It is suggested that biological methods are unsatisfactory for the study of influenza B virus recombinants, and should be replaced by biochemical techniques designed to trace the parental origins of individual RNA segments.