Influence of residual moisture and sealing atmosphere on viability of two freeze-dried viral vaccines

Abstract

This study demonstrated the complexity of the factors leading to changes in the infectivity titers of freeze-dried canine distemper and poultry infectious bronchitis viral vaccines. The change in moisture content during the storage period was an additional parameter which may influence the infectivity titer. The results emphasized the difficulty of predetermining variations in infectivity titers from the initial residual moisture. The analysis of the variations in infectivity titers during the storage of the two vaccines led to the formulation of a hypothesis of the presence of two components of different thermostability. Moreover, the temporary increase in the infectivity titer of infectious bronchitis vaccine stored at 6°C seemed to indicate the existence of aggregates of infectious particles progressively dissociating during storage concurrent with a progressive inactivation of infectious particles.