2026 ICD-10-CM Diagnosis Code T50.Z95AAdverse effect of other vaccines and biological substances, initial encounter

ICD-10-CM Codes›S00–T88›T36-T50›T50

ICD-10-CM T50.Z95A
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

T50.Z95A is a billable ICD-10-CM diagnosis code for adverse effect of other vaccines and biological substances, initial encounter. The 7th character A marks it as an initial encounter code, used while the patient is receiving active treatment. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 917 through 918. The code is not accepted as a principal diagnosis by the Medicare Code Editor. Coders also document this condition as adverse reaction caused by antiserum. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Adverse effects of drugs and medicaments, initial encounter.

Code Identity

ICD-10-CM Code
T50.Z95A
Billable Status
Yes — Valid for Submission
Code Describes
Adverse effect of other vaccines and biological substances, initial encounter
Short Description
Adverse effect of vaccines and biological substances, init
Parent Code
T50.Z95
Adverse effect of other vaccines and biological substances

Code Classification

ChapterS00–T88Injury, poisoning and certain other consequences of external causes
SectionT36-T50Poisoning by, adverse effect of and underdosing of drugs, medicaments and biological substances
CategoryT50Poisoning by, adverse effect of and underdosing of diuretics and other and unspecified drugs, medicaments and biological substances
This CodeT50.Z95AAdverse effect of other vaccines and biological substances, initial encounter

Code EditsBilling

Medicare Code Editor checks that affect claim validity for T50.Z95A.

Unacceptable principal diagnosis
There are selected codes that describe a circumstance which influences an individual's health status but not a current illness or injury, or codes that are not specific manifestations but may be due to an underlying cause. These codes are considered unacceptable as a principal diagnosis.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Adverse reaction caused by antiserum
  • Allergic reaction caused by vaccine product
  • Anaphylaxis caused by component of vaccine product
  • Encephalomyelitis caused by vaccine
  • Postvaccinal autoimmune reaction
  • Post-vaccination optic neuropathy
  • Thrombosis with thrombocytopenia syndrome following vaccination
  • Vaccine adverse reaction
  • VITT - vaccine-induced immune thrombotic thrombocytopenia

Coding GuidelinesGuidance

When coding an adverse effect of a drug that has been correctly prescribed and properly administered, assign the appropriate code for the nature of the adverse effect followed by the appropriate code for the adverse effect of the drug.

The appropriate 7th character is to be added to each code from block Poisoning by, adverse effect of and underdosing of diuretics and other and unspecified drugs, medicaments and biological substances (T50). Use the following options for the applicable episode of care:

  • A - initial encounter
  • D - subsequent encounter
  • S - sequela

Source: ICD-10-CM Official Guidelines for Coding and Reporting, FY 2026, published by CMS and the National Center for Health Statistics.

Clinical ClassificationClinical

AHRQ’s CCSR groups this code into broader clinical categories.

CCSR INJ028
Adverse effects of drugs and medicaments, initial encounter
Default principal diagnosis: inpatient No · outpatient Yes

Table of Drugs and ChemicalsClinical

Substances in the Table of Drugs and Chemicals that reference this code family. Always confirm in the Tabular List before coding.

SubstanceAccidentalSelf-harmAssaultUndeter­minedAdverse
Effect		Under­dosing
Glandular extract (medicinal) NECT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Pegademase, bovineT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NECT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::antineoplasticT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::bacterial NECT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::bacterial NEC::withT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::bacterial NEC::with::other bacterial componentT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::bacterial NEC::with::pertussis componentT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::bacterial NEC::with::viral-rickettsial componentT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::bacterial NEC::mixed NECT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::BCGT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::choleraT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::diphtheriaT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::diphtheria::with tetanusT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::diphtheria::with tetanus::and pertussisT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::influenzaT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::measlesT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::measles::with mumps and rubellaT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::meningococcalT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::mumpsT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::paratyphoidT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::pertussisT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::pertussis::with diphtheriaT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::pertussis::with diphtheria::and tetanusT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::pertussis::with other componentT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::plagueT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::poliomyelitisT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::poliovirusT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::rabiesT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::respiratory syncytial virusT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::rickettsial NECT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::rickettsial NEC::withT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::rickettsial NEC::with::bacterial componentT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::Rocky Mountain spotted feverT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::rubellaT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::sabin oralT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::smallpoxT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::TABT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::tetanusT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::typhoidT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::typhusT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::viral NECT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96
Vaccine NEC::yellow feverT50.Z91T50.Z92T50.Z93T50.Z94T50.Z95T50.Z96

Patient EducationClinical

Vaccine Safety

Vaccines play an important role in keeping us healthy. They protect us from serious and sometimes deadly diseases. Vaccines are injections (shots), liquids, pills, or nasal sprays that you take to teach your body's immune system to recognize and defend against harmful germs. The germs could be viruses or bacteria.

The full article covers:

  • What are vaccines?
  • Do vaccines cause side effects?
  • How are vaccines tested for safety?

Read the full article at MedlinePlus

Courtesy of MedlinePlus, a service of the U.S. National Library of Medicine.

Convert T50.Z95A to ICD-9-CMHistory

The closest ICD-9-CM equivalents under the General Equivalence Mappings.

ICD-9-CM
995.29 Adv eff med/biol NEC/NOS
ApproximateCombination The match is approximate, and more than one code can be needed to describe the source diagnosis. Confirm with contextual judgment.
ICD-9-CM
E949.9 Adv eff biologic NEC/NOS
ApproximateCombination The match is approximate, and more than one code can be needed to describe the source diagnosis. Confirm with contextual judgment.

Code HistoryHistory

FY 2016AddedAdded to the ICD-10-CM code setEffective October 1, 2015, the first year of ICD-10-CM.
FY 2017–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About T50.Z95AOverview

Is T50.Z95A (Adverse effect of other vaccines and biological substances) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report adverse effect of other vaccines and biological substances, initial encounter on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What does the 7th character A in T50.Z95A mean?

The final character A marks the initial encounter: use it while the patient is receiving active treatment for adverse effect of other vaccines and biological substances, such as an emergency visit or first evaluation.

What MS-DRG does T50.Z95A group to?

On inpatient claims, adverse effect of other vaccines and biological substances, initial encounter maps to MS-DRG 917, 918, with relative weights from 0.8571 to 1.5684 depending on complications. Higher weights mean higher Medicare reimbursement.

Can T50.Z95A be a principal diagnosis?

No. The Medicare Code Editor rejects this code as a principal diagnosis because adverse effect of other vaccines and biological substances, initial encounter describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.

What is the ICD-9 equivalent of T50.Z95A?

Under the General Equivalence Mappings, adverse effect of other vaccines and biological substances, initial encounter converts to ICD-9-CM 995.29 (adv eff med/biol NEC/NOS) and E949.9 (adv eff biologic NEC/NOS). The mapping is approximate, so confirm the match fits the documentation.

Footnotes

[1] Not chronic - A diagnosis code that does not fit the criteria for chronic condition (duration, ongoing medical treatment, and limitations) is considered not chronic. Some codes designated as not chronic are acute conditions. Other diagnosis codes that indicate a possible chronic condition, but for which the duration of the illness is not specified in the code description (i.e., we do not know the condition has lasted 12 months or longer) also are considered not chronic.