HL7 VXU Message: Immunization Records

HL7 VXU (Unsolicited Vaccination Record Update) messages transmit immunization and vaccination records from EHRs, pharmacies, and clinics to external systems — most commonly Immunization Information Systems (IIS), also known as immunization registries. The VXU^V04 is the single trigger event: an unsolicited update that reports one or more vaccinations a patient has received.

Segment	Name	Required	Purpose
MSH	Message Header	Yes	Sender, receiver, message type, version
PID	Patient Identification	Yes	Patient demographics and identifiers
PD1	Patient Additional Demographic	No	Registry/protection indicators, primary facility
NK1	Next of Kin / Associated Parties	No	Parent or guardian (common for pediatric records)
PV1	Patient Visit	No	Visit context for the encounter
ORC	Common Order	Yes	Order grouping for each vaccination (repeating)
RXA	Pharmacy/Treatment Administration	Yes	The vaccine administered (repeating)
RXR	Pharmacy/Treatment Route	No	Route and body site of administration
OBX	Observation/Result	No	Supporting observations (VIS dates, eligibility)

A VXU^V04 carries a repeating ORC + RXA group — one per vaccine administered — with optional RXR and OBX segments inside each group. A single message can therefore report an entire immunization history in one transmission.

RXA (Pharmacy/Treatment Administration) is the defining segment of a VXU message — it records the specific vaccine that was given. Key fields:

Field	Name	Purpose
RXA-3	Date/Time Start of Administration	When the vaccine was administered
RXA-5	Administered Code	The vaccine — typically a CVX code
RXA-6	Administered Amount	Dose quantity
RXA-7	Administered Units	Dose units (e.g., mL)
RXA-9	Administration Notes	Information source (e.g., new vs. historical record)
RXA-15	Substance Lot Number	Lot number of the vaccine product
RXA-16	Substance Expiration Date	Product expiration date
RXA-17	Substance Manufacturer Name	Manufacturer — typically an MVX code
RXA-18	Substance Refusal Reason	Reason if the vaccine was refused
RXA-20	Completion Status	CP (complete), RE (refused), NA (not administered), PA (partial)
RXA-21	Action Code	A (add), D (delete), U (update)

Vaccines in RXA-5 are coded with CVX (CDC vaccine administered codes); manufacturers in RXA-17 use MVX (CDC manufacturer codes). Both code sets are maintained by the CDC.

RXR (Pharmacy/Treatment Route) describes how the vaccine entered the body. It follows the RXA it relates to:

Field	Name	Example
RXR-1	Route	IM (intramuscular), SC (subcutaneous), IN (intranasal)
RXR-2	Administration Site	LD (left deltoid), RD (right deltoid), LVL/RVL (vastus lateralis)

OBX segments inside an ORC/RXA group carry observations that support the immunization record rather than lab results. Common uses include:

• Vaccine Information Statement (VIS) dates — the publication date and the date the VIS was presented to the patient
• Funding eligibility — whether the dose was VFC-eligible (Vaccines for Children) and the patient’s eligibility category
• Vaccine funding program / source — public vs. private stock
• Dose number and series-related observations

Each observation is linked to its vaccination by appearing within that vaccine’s segment group.

A single-vaccine immunization update sent to an immunization registry:

Browse the full HL7 sample messages catalog for more example messages — each one ready to copy as valid HL7 or download as a .hl7 file.

Code	Status	Meaning
CP	Complete	The vaccine was fully administered
PA	Partially Administered	A partial dose was given
RE	Refused	The patient or guardian refused the vaccine
NA	Not Administered	The vaccine was not given

RXA-9 (Administration Notes) distinguishes a newly administered dose from a historical record entered from an outside source. A code of 00 (new immunization record) means the sending system administered the vaccine, while 01 (historical information — source unspecified) and related codes indicate the dose was recorded from prior documentation. Registries treat the two differently — new administrations may carry lot and manufacturer detail that historical entries often lack.

Immunization registries expect standardized coding: CVX codes identify the vaccine in RXA-5, and MVX codes identify the manufacturer in RXA-17. Both code sets are published and maintained by the CDC. Integration engines mapping local vaccine catalogs to VXU output must keep these crosswalks current, since the CDC adds CVX codes as new vaccine products reach the market.

The canonical profile for VXU messaging is the CDC HL7 Version 2.5.1 Implementation Guide for Immunization Messaging. It constrains the base HL7 v2.5.1 standard — defining required fields, cardinalities, and value sets specifically for IIS reporting. Most state and regional immunization registries publish their own local addendum on top of this guide, so implementations should validate against both the CDC guide and the target registry’s specification.

A registry typically returns an ACK to confirm receipt of a VXU message. Beyond unsolicited updates, the immunization messaging guide also defines a query pair — QBP^Q11 (request an immunization history) and RSP^K11 (the registry’s response) — used when a provider needs to retrieve a consolidated history rather than report a new dose.