Question 1

What is ICD-10 code Z28.310?

Accepted Answer

Z28.310 is the ICD-10-CM diagnosis code for unvaccinated for covid-19. A patient has not received any COVID-19 vaccine doses. Z28.310 sits in the ICD-10-CM chapter for factors influencing health status and contact with health services (z00-z99), within the section covering persons with potential health hazards related to communicable diseases (z20-z29).

Z28.310 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.

This code specifically tracks unvaccinated COVID-19 status for public health monitoring.

Question 2

Is Z28.310 an HCC code?

Accepted Answer

No. Z28.310 is a billable ICD-10-CM code but does not map to any payment HCC category under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can still be reported on Medicare Advantage encounter data submissions, but it does not contribute to the beneficiary's Risk Adjustment Factor (RAF) score and therefore does not affect the risk-adjusted capitation payment to the plan. V28 reached 100% phase-in for payment year 2026.

Question 3

Is Z28.310 billable?

Accepted Answer

Yes. Z28.310 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. Z28.310 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Question 4

What is the V28 vs V24 difference for Z28.310?

Accepted Answer

Z28.310 does not map to a payment HCC under either the CMS-HCC V28 risk adjustment model or the older V24 model. V28 reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition. Because neither model rewards Z28.310 with a risk adjustment factor, it contributes zero to a Medicare Advantage beneficiary's RAF score in either version. Coders should check whether provider documentation supports a more specific child code that does map to a payment HCC.

Question 5

What should coders know when reporting Z28.310?

Accepted Answer

This code specifically tracks unvaccinated COVID-19 status for public health monitoring Distinguish from Z28.311 (partially vaccinated) based on number of doses received

Z28.310

Is Z28.310 an HCC code?

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Open Z28.310 in the Interactive Encoder