STUDIES ON A SIMPLIFIED POTENCY TEST OF INACTIVATED POLIOV-ACCINE AND AN ATTEMPT OF LYOPHILIZATION OF VACCINE

Abstract

Procedures of the newly devised mouse potency test of inactivated poliovirus vaccine are as follows: Mice are immunized intraperitoneally with two doses of each dilution of test vaccine separated by 3 days, They are challenged intraperitoneally with a fixed large dose of each type poliovirus after 4 days of second vaccination. Approximately 6 hours after the virus challenge they are bled by heart puncture. The individual heparinized blood is frozen-stored until tested, when the thawed whole blood is inoculated undiluted into each of two monkey kidney tissue culture tubes in 0.1ml amount. The tubes are incubated at 37°C and observed for specific CPE, final reading is made on 7 th day. Under these conditions virus titer of mouse blood in the unvaccinted control group used to fall in the range of 10² to 10³ TCD₅₀per 0.1ml. For the immunized mice, when neither of the inoculated tubes shows CPE, the mouse blood is considered as virus-negative. A ratio, number of mouse virus-negative vs. number of mouse tested, is obtained for each of vaccine dilutions. To indicate potency of vaccine 50% Antigenic Extinction Limiting Value is calculated by Reed & Muench's method using above-mentioned ratios.
This mouse potency test can considerably curtail time and labor for the work. In a number of experiments including repeated tests with same lots or vaccine this test has been shown to be an acceptable rapid method measuring immunogenicity of poliovaccine, especially, for orientation purpose of a study. Discussions on the sensitivity of the test have been given from our data described.
As for lyophilization of vaccine, a freeze-dried product having good potency as can be used as a reference purpose has been prepared by concentration of vaccine using Carbowax, dialysis against hypotonic salt solution and addition of Polyvinylpyrrolidone, Glycine and L-Hydroxyproline before lyophilization. Increase of thermostability of the lyophilized vaccine as compared with the original fluid vaccine has been demonstrated for Type 1 component in the 50°C heating test.