2026 ICD-10-CM Diagnosis Code Z28.310Unvaccinated for COVID-19

ICD-10-CM Codes›Z00–Z99›Z20-Z29›Z28

ICD-10-CM Z28.310
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

Z28.310 is a billable ICD-10-CM diagnosis code for unvaccinated for COVID-19. It is valid on HIPAA claims for fiscal year 2026 (October 1, 2025 through September 30, 2026). The code is not accepted as a principal diagnosis by the Medicare Code Editor and exempt from POA reporting. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under No immunization or underimmunization.

Code Identity

ICD-10-CM Code
Z28.310
Billable Status
Yes — Valid for Submission
Code Describes
Unvaccinated for COVID-19
Short Description
Unvaccinated for COVID-19
Same as the full description in the CMS dataset.
Parent Code
Z28.31
Underimmunization for COVID-19 status

Code Classification

ChapterZ00–Z99Factors influencing health status and contact with health services
SectionZ20-Z29Persons with potential health hazards related to communicable diseases
CategoryZ28Immunization not carried out and underimmunization status
This CodeZ28.310Unvaccinated for COVID-19

Code EditsBilling

Medicare Code Editor checks that affect claim validity for Z28.310.

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.

Present on Admission (POA)Billing

Z28.310 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.

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.

    • COVID-19
      • unvaccinated (for)
    • Status(post)
      • underimmunization
        • COVID-19
          • unvaccinated (for)
    • Underimmunization status
      • COVID-19
        • unvaccinated (for)
    • Unimmunized
      • for COVID-19
    • Unvaccinated
      • for COVID-19

Clinical ClassificationClinical

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

CCSR FAC017
No immunization or underimmunization
Default principal diagnosis: inpatient No · outpatient No

Patient EducationClinical

COVID-19 Vaccines

COVID-19 (coronavirus disease 2019) is an illness caused by a virus. This virus is a coronavirus called SARS-CoV-2. In the United States, there are several vaccines that are effective at protecting people from getting seriously ill, being hospitalized, and dying from COVID-19.

Read the full article at MedlinePlus

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

Code History & ChangesHistory

Replacement Z28.310 replaces the following previously assigned code(s):

  • Z28.3 - Underimmunization status
FY 2023AddedAdded to the ICD-10-CM code setEffective October 1, 2022.
FY 2024–2025No changes
FY 2026CurrentCurrent code set, no changesEffective October 1, 2025 through September 30, 2026.

Questions About Z28.310Overview

Is Z28.310 (Underimmunization for COVID-19 status) a billable code?

Yes. This is a billable ICD-10-CM code, specific enough to report unvaccinated for COVID-19 on HIPAA-covered claims from October 1, 2025 through September 30, 2026.

Can Z28.310 be a principal diagnosis?

No. The Medicare Code Editor rejects this code as a principal diagnosis because unvaccinated for COVID-19 describes a circumstance that influences health status rather than a current illness. Report it as a secondary diagnosis.

Is Z28.310 exempt from POA reporting?

Yes. CMS lists this code among those exempt from present on admission reporting, so hospitals do not assign a POA indicator for unvaccinated for COVID-19 on inpatient claims.

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.