https://confluence.hl7.org/display/PHWG/SMART+Health+Card+-+Vaccination+Credential+IG

The SMART Health Card (SHC) Vaccination and Testing IG (aka VCI IG) requests a variance for the Immunization FHIR resource.

The VCI IG requires "data minimization" (DM) profiles to allow all relevant data to be contained within a QR code to enable offline verification. Several US Core elements are mandatory, which are not required for the VCI IG use cases and may bloat the size of the FHIR bundle embedded within the QR code. The VCI IG defines "Allowable Data" profiles which usually do not explicitly restrict cardinality (to 0..0) for many elements. The DM profiles derive from the AD profiles and further restrict allowable elements (by restricting cardinality to 0..0). The AD profiles may align with most data elements within the corresponding US Core profile, but it is expected that the DM profiles in the VCI IG will vary.

We understand that a profile with an element with 0..0 cardinality cannot derive from a profile (i.e., US Core) that specifies cardinality for the same element as mandatory (1..*).

The MUST SUPPORT definition for the VCI IG is also geared toward a limited set of use cases, whereas US Core definition of MUST SUPPORT is designed for a much broader and different set of use cases.

The VCI IG, in order to support emerging international stakeholders, may need to support value sets using code systems other than US code systems like CVX. Also, compared to US Core, the VCI IG may need to specify different handling for using multiple codes with the CodeableConcept Datatype (i.e., coding array with alternate codes or translations