The influence of modifications in the potency of smallpox vaccines on the immunological reactivity of the organism.

The possible influence of shipment and storage conditions upon the potency of smallpox vaccines was investigated by testing the direct effect of vaccine potency on the type of cutaneous reaction and on the level of serum antibodies. Vaccine no. 1--freshly prepared, shipped and stored at +4 degrees C--proved to be more potent than vaccine no. 2, at the limit of its efficiency, shipped and maintained under usual conditions. To maintain the initial potency of smallpox vaccines it is recommended either to improve the shipment and storage conditions, or to use a lyophilized vaccine.