The effect of a rabies vaccine is mostly dependent upon the method of inactivating virus. Taking this fact into consideration, ultraviolet-irradiated inactivated vaccine (UV) was compared with vaccines prepared by conventional methods using phenol, merzonin (a Japanese proprietary name for sodium ethylmercurithiosalicylate), and formalin for inactivation and glycerin for attenuation.
Ultraviolet irradiation was carried out with the apparatus devised by Ando. The number of rotations per minute of the irradiation cylinder, the difference in height (in cm) between the fluid to be irradiated and the cylinder, and the inclination angle of the cylinder were so arranged as to make various combinations of factors for inactivation of virus. Samples of UV thus prepared were compared with those of vaccine inactivated by the other conventional agents, by calculating protection titers of these sample vaccines according to the Habel method.
As a result, it was revealed that the vaccine irradiated at 400 r. p.m., at a difference of 73cm, and at an angle of 30° was the most excellent of those inactivated by ultraviolet irradiation, showing a protection titer of 11, 165. Phenol-inactivated vaccine followed it with a protection titer of 10, 892. Next came merzonin-inactivated, glycerin-attenuated, and formalin-inactivated vaccines in the decreasing order of protection titer as listed. Therefore, the superiority of UV was confirmed. By comparing protection titers of samples of UV prepared with different conditions of ultraviolet irradiation, it was found that samples of high protection titer were mostly obtained from irradiation at a difference of 60 or 70 cm and an inclination angle of 20 to 30°.
UV was tested for keeping quality at 2 to 5°.
As a consequence, its potency was maintained 6 months after preparation and decreased a very little even 12 months after.
In short, UV is not inferior at all to the conventional vaccines prepared by other methods, in respe to safety and immunogenicity. The experimental results have made it possible to anticipate that a vaccine with more excellent immuno-genicity and keeping quality can be prepared by ultraviolet irradiation under appropriate conditions.
