2027 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 2027 ICD-10-CM dataset · Effective Oct 1, 2026 – Sep 30, 2027

Z28.310 is a billable ICD-10-CM diagnosis code for unvaccinated for COVID-19. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 951. 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 the other POA exempt codes in Persons with potential health hazards related to communicable diseases (Z20-Z29).

Instructional NotesGuidance

Instructions from the official ICD-10-CM Tabular List that apply to Z28.310: its own notes plus those printed at Z28.31, Z28.3, Z28, and Chapter 21. 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.

From Z28 Immunization not carried out and underimmunization status applies to 17 codes
  • vaccination not carried out

Use Additional Code

Add a second code, after this one, to fully describe the condition.

From Z28.3 Underimmunization status applies to 3 codes
  • code, if applicable, to identify:
  • immunization not carried out because of contraindication (Z28.0-)
  • immunization not carried out because of patient decision for other and unspecified reason (Z28.2-)
  • immunization not carried out because of patient decision for reasons of belief or group pressure (Z28.1)
  • immunization not carried out for other reason (Z28.8-)

Code Also

A second code may be needed to fully describe the condition; the note gives no sequencing direction.

From Z28 Immunization not carried out and underimmunization status applies to 17 codes
  • if applicable, encounter for immunization safety counseling (Z71.85)

Notes

General instructions on how these codes are used.

From Z28.31 Underimmunization for COVID-19 status applies to 2 codes
  • These codes should not be used for individuals who are not eligible for the COVID-19 vaccines, as determined by the healthcare provider.
From Chapter 21 (Z00-Z99) Factors influencing health status and contact with health services applies to 1,425 codes
  • Z codes represent reasons for encounters. A corresponding procedure code must accompany a Z code if a procedure is performed. Categories Z00-Z99 are provided for occasions when circumstances other than a disease, injury or external cause classifiable to categories A00-Y89 are recorded as 'diagnoses' or 'problems'. This can arise in two main ways:
  • (a) When a person who may or may not be sick encounters the health services for some specific purpose, such as to receive limited care or service for a current condition, to donate an organ or tissue, to receive prophylactic vaccination (immunization), or to discuss a problem which is in itself not a disease or injury.
  • (b) When some circumstance or problem is present which influences the person's health status but is not in itself a current illness or injury.

Source: CMS ICD-10-CM Tabular List. How to read instructional notes.

Referenced in Other NotesGuidance

Instructional notes printed at other codes that name Z28.310, its category, or a range that includes it.

Code Also 1

These codes say Z28.310 may also be needed to fully describe the condition. The note gives no sequencing direction.

  • Z71.85 Encounter for immunization safety counseling
    if applicable, immunization not carried out (Z28.-) names Z28.-, which includes this code

Index to Diseases and InjuriesGuidance

Alphabetical index entries that point to this code.

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. Most people with COVID-19 have mild symptoms, but some people become very sick. You can protect yourself by getting a COVID-19 vaccine. The vaccines might help keep you from getting sick 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 2024–2026No changes
FY 2027CurrentCurrent code set, no changesEffective October 1, 2026 through September 30, 2027.

Questions About Z28.310Overview

What is the ICD-10 code for unvaccinated for COVID-19?

The ICD-10-CM code for unvaccinated for COVID-19 is Z28.310 (sometimes written as Z28310). It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.

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, 2026 through September 30, 2027.

What MS-DRG does Z28.310 group to?

On inpatient claims, unvaccinated for COVID-19 maps to MS-DRG 951 (other Factors Influencing Health Status), which carries a relative weight of 0.5574. Higher weights mean higher Medicare reimbursement.

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. The code appears in the Persons with potential health hazards related to communicable diseases (Z20-Z29) range of the CMS exempt list.