Studies on Lyophilization of Sabin Vaccine. 2. Investigation on Long Time Incubation at High and Low Temperatures of Lyophilized Sabin Vaccine

Lyophilization of vaccine is one of the possible options for the development of a heat-stable poliovaccine. In our previous study in which conditions affecting the lyophilization of Sabin poliovaccine were investigated, it was found that infectivity titration of lyophilized viruses was under at least three kind of variabilities i. e., i) the variability among different lyophilization experi-ments, ii) the variability within the same lyophilization experiment and iii) the variability inherent to virus titration experiments. In the present study, experiments on lyophilization of three types of Sabin vaccine virus and long time incubation of the lyophilized vaccine viruses at relatively high and low temperatures were carried out, taking great care to minimize the afore-mentioned variabilities and using the optimum conditions for lyophilization found in the previous study. The results showed that lyophilization greatly increased the heat-stability of Sabin vaccine and that type 1, 2 and 3 lyophilized vaccine viruses withstood one week at 37°C with an average loss of infectivity of 0.53 log, 0, 0.55 log10 and 0.39 log10, respectively