Table 3.

Immunization identifiers excluded from the crosswalk

Immunization	Legacy System	Future EMR	Justification for exclusion
Purified protein derivative (PPD)	2	0	Not a vaccine: The PPD is not an immunization, although it is some-times treated as one [50]. The legacy system only provided the PPD administration date and PPD evaluation date, not the actual PPD result.*
TdaP, cocoon	2	0	Data validity concern: TdaP cocooning immunizations are given to new mothers (in some research protocols other caregivers), to protect newborns from pertussis [51]. We have 4800 births per year in our hospital system, yet only 19 ‘TdaP, cocoon’ instances, of which eight are recorded for men or women who were not of childbearing age.
Typhoid, generic	1	0	Data validity concern: We could not determine if the immunizations were oral typhoid or injectable typhoid and the follow-up for these immunizations is different [52]. Medical use concern: All patients with ‘typhoid’ immunizations recorded in our legacy system would need a booster before travelling again [52].
Encephalitis, generic	0	1	Crosswalk validity concern: No CVX code for generic encephalitis.
Influenza, specific formulations	0	4	Legacy system drawback: The legacy systems immunization identifier for influenza did not differentiate preservative vs. preservativefree or whole vs. split product influenza. To decrease the complexity of data entry for seasonal influenza within the future EMR we used: • 1 identifier for injectable influenza • 1 identifier for intranasal influenza • 1 identifier for high-dose influenza

^*Because PPD records were excluded before data extraction this data is not included in our analysis of the system crosswalk.