A number of issues here:

• The C-CDA to FHIR Immunizations mapping page lists the FHIR->CDA concept map instead of the CDA->FHIR concept map
• Neither of these concept maps appear on the list of terminology maps
• Both of these concept maps appear woefully incomplete (though.... so does the example FHIR value set; the code system, at least, has more values - but it's the v3 ActSite system which seems less useful that just preserving the original SNOMED value from C-CDA)

Additionally, no vendors provided examples of mapping this C-CDA->FHIR, it is only a MAY in C-CDA, and it is not mentioned in US Core. (I don't disagree with the field-mapping logically - these are equivalent fields; there are just several issues with the current concept mapping guidance).