1961 年 11 巻 4 号 p. 257-266
Attenuation of the Okuda and Kinugasa strains of influenza A2 virus, isolated in our laboratory in 1957, was attempted by egg passage, using chiefly 10 or 11 day eggs. Mainly 10-3 dilution of infected chorio-allantoic fluid was used as inoculum for serial passage. Infected chorio-allantoic fluids of various generations of egg passage were inoculated by inhalation or instillation method to human volunteers. For inhalation, an outlet of a nebulizer with an air compresser was kept 1-2cm apart from the nostrils of volunteers, and fine mist was inhaled by deep or normal breathing for 10 or 60sec. Instillation method was far less efficient than inhalation method, and only inhalation method was used in the following experiments.
The Okuda strain of the 3rd and the Kinugasa strain of 7th egg passage provoked typical signs of influenza. The materials of about 100th passage of these strains proved to have little pathogenicity, while antigenicities of them were well preserved (Table 1, 2).
Egg infectious titer of materials and inhalation time were important factors. When the titer was low, hemagglutination inhibiting (HI) antibody was poorly provoked in the subjects. When the titer was high and the material was inhaled for 60sec., some persons showed transient fever without local catarrhalic sign. When the inoculum was not so high, general toxic reactions were negligible (Table 3). Not only HI antibody, but other antibodies increased (Table 4). The persons with clinical signs such as fever, headache or lassitude, showed far poorer antibody response, than those without clinical sign.
Reisolation of virus from inoculated persons was unsuccessfuland infection to others from them was not observed. The S-antibody rise and the small quantities of virus needed for antibody response seem to show active propagation of influenza virus in human volunteers. No significant difference was observed between these two strains.
The strains and the inoculation method are hopeful to be used as live influenza vaccination.