CVX (Vaccine Administered Codes)

terminology system technical clinicalhealthcareinteroperabilityfhir

Acronym for: Vaccine Administered Codes

Source: CDC System: http://hl7.org/fhir/sid/cvx Code: CVX Reviewed: 20/01/2026 License: CC-BY-4.0

CVX (Vaccine Administered Codes)

One-sentence definition: CVX is a freely available, CDC-maintained numeric code set that identifies the type of vaccine product administered to a patient — independent of manufacturer or package — enabling consistent immunization data exchange between EHRs, immunization information systems, and public health registries.

Full Definition

CVX codes identify vaccine types at the level that matters for clinical and public health purposes: the antigen and formulation, not the specific package or lot. CVX 207, for example, identifies the Moderna mRNA COVID-19 vaccine; CVX 208 identifies the Pfizer-BioNTech mRNA COVID-19 vaccine. Each distinct vaccine product has its own CVX code, but a single code covers all package sizes and manufacturers for that product — because the clinical and epidemiological significance is in the vaccine type, not the packaging.

CVX is maintained by the Centers for Disease Control and Prevention (CDC), National Center for Immunization and Respiratory Diseases (NCIRD), and published in coordination with HL7. It is freely available in the public domain — no licensing fees, no registration required. CVX codes are distributed as a flat table updated as needed when new vaccines are approved for clinical use.

In the FHIR ecosystem, CVX is the standard coding system for the Immunization.vaccineCode element in the US Core Immunization profile. It is also used in immunization information system (IIS) transactions — the state and territorial registries where vaccination records are reported, aggregated, and queried for immunization history.

Context and Usage

Where This Term Appears

CVX appears throughout immunization data workflows:

  • FHIR resources: Immunization.vaccineCode — the primary element identifying what vaccine was given
  • Immunization information systems (IIS): HL7 v2 VXU (Vaccination Update) messages and FHIR-based IIS integrations both use CVX
  • Public health reporting: syndromic surveillance, vaccine coverage reporting, and outbreak investigation data use CVX to identify vaccine types
  • US Core Immunization profile: CVX is required for conformant FHIR immunization records
  • CMS quality measures and HEDIS: immunization measures reference CVX codes to identify whether specific vaccines were administered

Common Usage Examples

In conversation: “The IIS expects CVX codes — our source system uses NDC, so we need to map at the interface layer before we can submit.”

In documentation: “The Immunization.vaccineCode must be populated with a CVX code using system http://hl7.org/fhir/sid/cvx to satisfy US Core conformance.”

In technical contexts — a FHIR Immunization resource using CVX:

{
  "resourceType": "Immunization",
  "status": "completed",
  "vaccineCode": {
    "coding": [
      {
        "system": "http://hl7.org/fhir/sid/cvx",
        "code": "207",
        "display": "COVID-19, mRNA, LNP-S, PF, 100 mcg/0.5 mL dose"
      }
    ]
  },
  "patient": {
    "reference": "Patient/example"
  },
  "occurrenceDateTime": "2021-03-15"
}

Why CVX Exists

Before standardized vaccine codes, immunization records were exchanged using NDC (National Drug Codes), which identify specific packaged products — the exact formulation, package size, and manufacturer for a specific production lot. NDC is suitable for dispensing and inventory management, but it creates fragmentation for immunization records: the same vaccine from two manufacturers has different NDC codes, even though the clinical significance is identical for immunization coverage purposes.

The CDC developed CVX to provide a stable, product-type identifier for vaccines that remains consistent across manufacturers and package sizes. This allows immunization registries to aggregate vaccination records from multiple providers and source systems without needing to maintain manufacturer-specific mapping tables.

Key Characteristics

Numeric Codes

CVX codes are short numeric values (one to three digits). Unlike the structured alphanumeric format of ICD-10 or the long numeric format of SNOMED CT, CVX codes have no internal structure — the number is an opaque identifier, not a classification hierarchy. CVX 21 is varicella vaccine; CVX 33 is pneumococcal polysaccharide vaccine (PPSV23); CVX 207 is mRNA COVID-19 (Moderna). The numbers do not encode a classification.

CDC Maintenance

The CDC updates CVX as new vaccines enter clinical use. Code table releases are versioned and dated; the current table is publicly available from the CDC’s IIS Standards website. New vaccine products are added before or shortly after FDA approval. Retired codes (for vaccines no longer in use) are marked inactive but retained in the table so historical records remain interpretable.

Vaccine Product Identification

CVX identifies the vaccine product at the level of antigen and formulation. For vaccines available in multiple formulations (pediatric vs adult dose, adjuvanted vs non-adjuvanted), separate CVX codes distinguish the clinically significant variants. For vaccines with multiple manufacturers using the same formulation, a single CVX code covers all manufacturers — manufacturer identity is captured in the companion MVX (Manufacturer) code.

CVX and FHIR

Immunization Resource

The FHIR Immunization resource uses vaccineCode to identify what was administered. US Core requires CVX for this element. The coding system URI is http://hl7.org/fhir/sid/cvx. Most US-market EHRs maintain a CVX code table and populate this element from charge capture or administration records.

A single vaccineCode can carry multiple codings — CVX for the vaccine type and NDC for the specific product dispensed are commonly paired in a CodeableConcept, satisfying both public health reporting requirements (CVX) and pharmacy dispensing tracking (NDC).

VaccineCode Element

Immunization.vaccineCode is a CodeableConcept — it can hold multiple codings from different systems. The US Core Immunization profile requires at least one coding with system http://hl7.org/fhir/sid/cvx. Additional codings for NDC or manufacturer-specific codes can be included alongside CVX without violating conformance requirements.

Technical Considerations

Free and Public Domain

CVX is not subject to licensing restrictions. The CDC publishes the code table freely; organizations can download, redistribute, embed in products, and use CVX codes in commercial software without fees or agreements. This distinguishes CVX from CPT (AMA-licensed) and SNOMED CT (national licensing), making it straightforward to include in any product that handles immunization data.

Relationship to NDC and MVX

The three coding systems form complementary layers for vaccine identification:

  • CVX: vaccine product type — what antigen and formulation was given (clinical and public health significance)
  • MVX: manufacturer — who made the vaccine (supplemental, used when manufacturer tracking matters)
  • NDC: specific packaged product from a specific manufacturer — the physical item that was dispensed

IIS and public health reporting uses CVX as the primary identifier. Pharmacy systems use NDC for dispensing. A complete immunization record may carry all three, linked within a single vaccineCode CodeableConcept.

Relationship to Other Terms

  • FHIR — CVX is the required coding system for Immunization.vaccineCode in FHIR US Core profiles
  • LOINC — LOINC codes immunization-related observations (e.g., serological test results); CVX codes the administered vaccine itself

Common Misconceptions

Misconception 1: CVX Identifies Vaccine Manufacturers

  • Incorrect belief: Each CVX code identifies a specific manufacturer’s version of a vaccine — so Moderna and Pfizer COVID-19 vaccines have different CVX codes because of the manufacturer.
  • Reality: CVX codes identify the vaccine type (antigen and formulation), not the manufacturer. Moderna and Pfizer mRNA COVID-19 vaccines have different CVX codes (207 and 208) because their formulations differ clinically, not because of the manufacturer. Two vaccines with identical formulations from different manufacturers would share a CVX code. Manufacturer identity is tracked separately using MVX codes.
  • Why it matters: Implementations that expect one-to-one CVX-to-manufacturer mapping will produce incorrect results when multiple manufacturers supply the same formulation. Design immunization workflows to treat CVX as formulation-type identifier and MVX as manufacturer identifier — separate concerns.

Misconception 2: CVX is Only for COVID-19 Vaccines

  • Incorrect belief: CVX codes were developed in response to COVID-19 and primarily cover COVID-19 vaccines.
  • Reality: CVX has been in use since the early 1990s and covers the entire US vaccine schedule — childhood immunizations (DTaP, MMR, varicella, hepatitis B, Hib, rotavirus, PCV, IPV), adult vaccines (influenza, pneumococcal, zoster, Td/Tdap), travel vaccines, and specialty vaccines. COVID-19 vaccines received new CVX codes when they were authorized, but they are a small fraction of the overall code table.
  • Why it matters: Immunization information systems expecting only COVID-19 CVX codes will fail to report historical vaccination records. Any system handling comprehensive immunization histories needs the full CVX code table.

Why CVX Matters

CVX is the interoperability foundation for immunization data exchange in the US. It enables a vaccination record created in one EHR to be understood by a state immunization registry, a school health system, a travel medicine clinic, and a public health surveillance system — all using the same vaccine type identifier. For FHIR implementations, CVX conformance in the Immunization.vaccineCode element is what makes immunization records portable and computationally interpretable outside the originating system.

Cross-References

  • FHIR — the data exchange standard that requires CVX in its Immunization resource profiles
  • LOINC — the observation coding system used for immunization-related assessments and serological results

Last reviewed: January 20, 2026 Definition authority: CDC Content status: Canonical reference