Neuraminidase (NA) activity of 10 strains of influenza A and 10 strains of influenza B virus was determined by fluorometric and colorimetric assays using 4-methylumbelliferyl (4-MU)-N-Ac-α-D-neuraminide and fetuin as the substrate, respectively. The ratio of NA activity measured by colorimetric assay to that measured by fluorometric assay was significantly higher with influenza B virus than with influenza A virus. When measured by fluorometric assay, NA activity of influenza A virus was strongly inhibited by etylenediaminetetraacetate, while that of influenza B virus was not. Influenza B virus NA was also significantly less susceptible to competitive inhibition by N-acetylneuraminic acid than influenza A virus NA, suggesting the different substrate specificity of the two NAs. It is worth to note that such an enzymological heterogeneity between influenza A and B virus NAs is demonstrated only by the use of a low molecular weight synthetic substrate, 4-MU-N-Ac-α-D-neuraminide and fluorometric assay.
Inactivated poliomyelitis vaccines were prepared with each type of concentrated and purified attenuated and virulent viruses (Sabin 1, 2, 3, Mahoney, Brunhilde, MEF-1 and Saukett). During inactivation period with formalin, no significant difference were observed for the decrease of virus infectivity between Sabin and virulent viruses. By analysis of D antigen content with gel diffusion test befor and during inactivation period, type 1 Mahoney showed instability and could be recovered only 29% of D antigen at the end of inactivation period, but Sabin type 1 showed good stability as well as other types of Sabin and virulent viruses. In immunization tests with guinea pigs, inactivated Sabin viruses induced good seroconversion against not only homologous Sabin virus but also virulent virus. These results indicate that it seems possible to make inactivated poliomyelitis vaccine with Sabin viruses having comparable immunogenicity to the vaccine from virulent viruses. By use of attenuated virus the safety of the vaccine is improved and the vaccine can be prepared in the facilities in which live oral vaccine is producing.