2026 ICD-10-CM Diagnosis Code B03Smallpox

ICD-10-CM Codes›A00–B99›B00-B09›B03

ICD-10-CM B03
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

B03 is a billable ICD-10-CM diagnosis code for smallpox. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026) and groups to MS-DRG 865 through 866. Coders also document this condition as alastrim. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Viral infection.

Code Identity

ICD-10-CM Code
B03
Billable Status
Yes — Valid for Submission
Code Describes
Smallpox
Short Description
Smallpox
Same as the full description in the CMS dataset.
Chapter
B00-B09
Viral infections characterized by skin and mucous membrane lesions

Code Classification

ChapterA00–B99Certain infectious and parasitic diseases
SectionB00-B09Viral infections characterized by skin and mucous membrane lesions
CategoryB03Smallpox
This CodeB03Smallpox

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Alastrim
  • Flat-type smallpox
  • Hemorrhagic smallpox
  • Modified smallpox
  • Smallpox
  • Smallpox without rash
  • Variola major

Tabular List NotesGuidance

Coding notes and annotation back-references applicable to this code.

  • In 1980 the 33rd World Health Assembly declared that smallpox had been eradicated.
  • The classification is maintained for surveillance purposes.

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

External Cause of Injuries IndexGuidance

References for this code in the External Cause of Injuries Index.

    • Alastrim
    • Smallpox
    • Variola(major) (minor)
    • Varioloid

Clinical ClassificationClinical

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

CCSR INF008
Viral infection
Default principal diagnosis: inpatient Yes · outpatient Yes

Clinical InformationClinical

  • Smallpox

    an acute, highly contagious, often fatal infectious disease caused by an orthopoxvirus characterized by a biphasic febrile course and distinctive progressive skin eruptions. vaccination has succeeded in eradicating smallpox worldwide. (dorland, 28th ed)

  • 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).

  • Variola virus

    a species of orthopoxvirus causing infections in humans. no infections have been reported since 1977 and the virus is now believed to be virtually extinct.

  • Orthopoxvirus

    a genus of the family poxviridae, subfamily chordopoxvirinae, comprising many species infecting mammals. viruses of this genus cause generalized infections and a rash in some hosts. the type species is vaccinia virus.

  • Modified Smallpox

    smallpox that occurs in an individual who has been vaccinated.

  • MVA-BN Smallpox Vaccine|Imvamune|Imvanex|JYNNEOS|MVA Smallpox Vaccine|Modified Vaccinia Ankara - Bavarian Nordic Smallpox Vaccine|Modified Vaccinia Ankara Smallpox Vaccine|VACCINIA VIRUS MODIFIED STRAIN ANKARA-BAVARIAN NORDIC NON-REPLICATING ANTIGEN

    a vaccine consisting of modified vaccinia ankara-bavarian nordic (mva-bn), a live, attenuated, non-replicating, proprietary version of the mva virus, used for the prevention of smallpox and monkeypox, with potential antineoplastic activity. upon intratumoral administration, mva-bn smallpox vaccine may induce both cellular and humoral immune responses, which may lead to tumor cell lysis.

  • Smallpox

    a condition that is caused by infection with variola, and that is characterized by small, raised bumps.

  • Variola Virus|Smallpox Virus|Smallpox Virus|VARIOLA VIRUS|Variola Virus VAR

    an orthopoxvirus that is the causative agent of smallpox.

  • Alastrim

    a orthopoxvirus that causes a milder clinical syndrome than smallpox.

Patient EducationClinical

Smallpox

Smallpox is a disease caused by the Variola major virus. Some experts say that over the centuries it has killed more people than all other infectious diseases combined. Worldwide vaccination stopped the spread of smallpox three decades ago. The last case was reported in 1977. Two research labs still keep small amounts of the virus.

Read the full article at MedlinePlus

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

Convert B03 to ICD-9-CMHistory

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

ICD-9-CM
050.0 Variola major
Approximate The match is approximate rather than exact.
ICD-9-CM
050.1 Alastrim
Approximate The match is approximate rather than exact.
ICD-9-CM
050.9 Smallpox NOS
Approximate The match is approximate rather than exact.

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 B03Overview

Is B03 (Smallpox) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report smallpox on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

What MS-DRG does B03 group to?

When smallpox is the principal diagnosis on an inpatient stay, it groups to MS-DRG 865, 866, with relative weights from 0.8696 to 1.4983 depending on complications. Higher weights mean higher Medicare reimbursement.

What is the ICD-9 equivalent of B03?

Under the General Equivalence Mappings, smallpox converts to ICD-9-CM 050.0 (variola major), 050.1 (alastrim), and 050.9 (smallpox 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.