Stratified and cryogenically stored (SACS) vaccines, a new concept in emergency foot-and-mouth disease vaccine formulation and storage.

Strategic reserves of foot-and-mouth disease (FMD) antigen have become an integral part of FMD control policy for many countries. They are based on two principles, ready formulated vaccine stored at +4 degrees C, or concentrated antigen preparations held at ultra-low temperature for later formulation. However, the latter is more economical, since ready formulated vaccine, based on oil or aluminium hydroxide/saponin adjuvants, requires regular replacement. This is primarily the result of the vaccine's limited shelf-life, nominally 18 months at +4 degrees C. Unfortunately, lowering the temperature of storage, in a bid to extend its shelf-life, has a detrimental effect on the vaccine's potency. Montanide ISA 206 and 25, two 'ready-to-formulate' oil adjuvants which can be used in all target species, are ideal for emergency vaccination. Their potential is enhanced by the ease in which they are formulated into oil emulsion vaccines. Here we describe a novel approach of layering the individual components of FMD vaccine in the same primary container and then storing the product at ultra-low temperature. This avoids the detrimental effect on potency, normally observed with frozen formulated FMD vaccine, and could substantially extend the products shelf-life. The implications of this approach for emergency vaccination strategy are discussed.