2026 ICD-10-CM Diagnosis Code Z28.311Partially vaccinated for COVID-19

ICD-10-CM Codes›Z00–Z99›Z20-Z29›Z28

ICD-10-CM Z28.311
CMSSource: CMS FY 2026 ICD-10-CM dataset · Effective Oct 1, 2025 – Sep 30, 2026

Z28.311 is a billable ICD-10-CM diagnosis code for partially vaccinated 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. Coders also document this condition as immunization series incomplete. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under No immunization or underimmunization.

Code Identity

ICD-10-CM Code
Z28.311
Billable Status
Yes — Valid for Submission
Code Describes
Partially vaccinated for COVID-19
Short Description
Partially vaccinated 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 CodeZ28.311Partially vaccinated for COVID-19

Code EditsBilling

Medicare Code Editor checks that affect claim validity for Z28.311.

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

Z28.311 is exempt from POA reporting on inpatient claims to general acute care hospitals. Review other POA exempt codes.

Approximate SynonymsGuidance

Alternate terms and clinical phrases that map to this code.

  • Immunization series incomplete
  • Partial vaccination for COVID-19
  • Requires first booster dose of SARS-CoV-2 vaccine
  • Requires second booster dose of SARS-CoV-2 vaccine
  • Requires third booster dose of SARS-CoV-2 vaccine
  • SARS-CoV-2 initial immunization series incomplete

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
      • partially vaccinated (for)
    • Immunization
      • partial
        • for COVID-19
    • Status(post)
      • underimmunization
        • COVID-19
          • partially vaccinated (for)
    • Underimmunization status
      • COVID-19
        • partially vaccinated (for)
    • Vaccination(prophylactic)
      • partial
        • 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 Z28.311 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 Z28.311Overview

Is Z28.311 (Underimmunization for COVID-19 status) a billable code?

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

Can Z28.311 be a principal diagnosis?

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

Is Z28.311 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 partially vaccinated 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.