2027 ICD-10-CM Diagnosis Code T50.B15SAdverse effect of smallpox vaccines, sequela
T50.B15S is a billable ICD-10-CM diagnosis code for adverse effect of smallpox vaccines, sequela. The 7th character S marks it as a sequela code, which reports a problem that remains after the original condition has resolved. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 922 through 923. The code is not accepted as a principal diagnosis by the Medicare Code Editor and exempt from POA reporting. Coders also document this condition as adverse reaction to smallpox vaccine. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Poisoning/toxic effect/adverse effects/underdosing, sequela.
Code Identity
Code Classification
Code EditsBilling
Medicare Code Editor checks that affect claim validity for T50.B15S.
Present on Admission (POA)Billing
T50.B15S is exempt from POA reporting on inpatient claims to general acute care hospitals. Review the other POA exempt codes in Poisoning by, adverse effect of and underdosing of drugs, medicaments and biological substances (T36-T50).
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Adverse reaction to smallpox vaccine
- Encephalitis caused by smallpox vaccine
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 2027, published by CMS and the National Center for Health Statistics.
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to T50.B15S: its own notes plus those printed at T50, block T36-T50, and Chapter 19. A note printed at a category, block or chapter applies to every code under it.
Includes
Further defines, or gives examples of, the content of the category.
- adverse effect of correct substance properly administered
- poisoning by overdose of substance
- poisoning by wrong substance given or taken in error
- underdosing by (inadvertently) (deliberately) taking less substance than prescribed or instructed
Excludes1
Not coded here: the excluded code is never reported together with this one, unless the two conditions are unrelated.
- toxic reaction to local anesthesia in pregnancy (O29.3-)
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
Code First
The underlying condition named in the note is sequenced before this code.
Use Additional Code
Add a second code, after this one, to fully describe the condition.
- code to identify any retained foreign body, if applicable (Z18.-)
Notes
General instructions on how these codes are used.
- Use secondary code(s) from Chapter 20, External causes of morbidity, to indicate cause of injury. Codes within the T section that include the external cause do not require an additional external cause code
- The chapter uses the S-section for coding different types of injuries related to single body regions and the T-section to cover injuries to unspecified body regions as well as poisoning and certain other consequences of external causes.
7th Character
Every code in the category takes a 7th character from the listed values, with the placeholder X filling any empty positions before it.
- The appropriate 7th character is to be added to each code from category T50
- Ainitial encounter
- Dsubsequent encounter
- Ssequela this code
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Referenced in Other NotesGuidance
Instructional notes printed at other codes that name T50.B15S, its category, or a range that includes it.
Use Additional Code 3
These codes say to use an additional code from the note, and T50.B15S is one of the codes named.
- G04.02 Postimmunization acute disseminated encephalitis, myelitis and encephalomyelitiscode to identify the vaccine (T50.A-, T50.B-, T50.Z-) names T50.B-, which includes this code
- G04.32 Postimmunization acute necrotizing hemorrhagic encephalopathycode to identify the vaccine (T50.A-, T50.B-, T50.Z-) names T50.B-, which includes this code
- G61.1 Serum neuropathycode for adverse effect, if applicable, to identify serum (T50.-) names T50.-, which includes this code
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Smallpox Vaccine
a vaccinia virus vaccine used for immunization against smallpox. it is now recommended only for laboratory workers exposed to smallpox virus. certain countries continue to vaccinate those in the military service. rare complications most often associated with older generation smallpox vaccines include vaccinia, secondary bacterial infections, and encephalomyelitis. because monkeypox virus and smallpox virus are both orthopoxvirus and are closely related smallpox vaccines provide effective cross-protection against mpox, monkeypox (https://www.cdc.gov/poxvirus/monkeypox/clinicians/smallpox-vaccine.html).
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.
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.B15S to ICD-9-CMHistory
The closest ICD-9-CM equivalents under the General Equivalence Mappings.
Code HistoryHistory
Questions About T50.B15SOverview
What is the ICD-10 code for adverse effect of smallpox vaccines, sequela?
The ICD-10-CM code for adverse effect of smallpox vaccines, sequela is T50.B15S (sometimes written as T50B15S). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is T50.B15S (Adverse effect of smallpox vaccines) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report adverse effect of smallpox vaccines, sequela on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What does the 7th character S in T50.B15S mean?
The final character S makes this a sequela code: it reports a lingering problem that remains after the adverse effect of smallpox vaccines itself has resolved, not the original event.
What MS-DRG does T50.B15S group to?
On inpatient claims, adverse effect of smallpox vaccines, sequela maps to MS-DRG 923, 922, with relative weights from 0.9980 to 1.6248 depending on complications. Higher weights mean higher Medicare reimbursement.
Can T50.B15S be a principal diagnosis?
No. The Medicare Code Editor rejects this code as a principal diagnosis because adverse effect of smallpox vaccines, sequela describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.
