I am unable to find a metadata element for Immunization to indicate the source of the vaccine administered. In some cases, the source is private stock purchased by the provider. Other times the source is a guarantee program from public health or other entities. Tracking the source of the vaccine is essential to assure compliance with rules for managing inventory and replenishment. Such rules may be internal to a practice or requires by the guarantee program's management structure. While there is a .note metadata element, there should be a specific element to allow specification in some structured form about the origin of the vaccine dose that was administered. Lot number and manufacturer are not sufficient to handle this reference to source since the same lot number may be part of private stock and guarantee program stock. Mixing inventory can be quite problematic depending on the program. While this issue may be US Realm specific, a generic ability to refer to a vaccine source should be acceptable internationally - local or realm-specific profiles can address the value set bindings needed, if any.