Freeze-drying various attenuated strains of Pasteurella pestis

A method is described for the preparation of freeze-dried living attenuated Pasteurella pestis organisms in a medium suitable for the development of a vaccine for human use. Viability recovery rates of 50% or greater were obtained with the attenuated strains of P. pestis when concentrates prepared from organisms harvested after 28-hr incubation were suspended in a sucrose-phosphate-glutamate solution containing 2.5% human serum albumin and freeze-dried. The freeze-dried organisms demonstrated no loss in viability after storage for 1 year at −20 °C.