Billing Medicare Part B for Flu and COVID-19 Vaccines: A Pharmacy Guide for Flu Season

Flu season means a steady line of Medicare patients rolling up their sleeves for a flu shot, a COVID-19 vaccine, or both. The upside for patients is great: when these claims are billed correctly, Medicare Part B covers them at $0 out of pocket. No copay, no coinsurance, and the Part B deductible doesn't apply.

The catch is that flu and COVID-19 vaccines are billed as medical claims under Part B, not through the pharmacy benefit most teams bill day to day. That means a different form, different codes, and a different set of ways a claim can get denied. Here's what your pharmacy needs to know to get these claims right the first time.

Not every vaccine belongs to Part B

Getting this one decision right at the front end prevents most vaccine claim denials.

A Part D vaccine billed as a medical claim will be denied. The reverse is also true: a Part B vaccine won't process correctly through the pharmacy benefit. When in doubt, check the list before you bill.

How Medicare covers flu and COVID-19 vaccines

Flu: Medicare covers one vaccine per flu season, with additional doses covered when medically necessary. A season, not a calendar year, is the unit that matters. A patient vaccinated in October and again the following September has had one shot in each of two separate seasons, and both are covered.

COVID-19: Medicare covers COVID-19 vaccines and additional doses in line with current FDA and CDC recommendations. There's no once-per-year cap the way there is for flu.

Both use diagnosis code Z23 ("encounter for immunization").

Giving flu and COVID-19 on the same day? Medicare requires modifier 59 on the second administration code. It's a small detail, but missing it is one of the most common reasons a same-day claim gets denied.

Current Flu vaccine billing rates

Admin-code rates (G0008/M0201) are locality-adjusted; find your locality's pricing by visiting the CMS's Vaccine Pricing page.

The billing details that actually cause denials

Vaccine claims are some of the cleanest claims in medical billing, but a handful of recurring issues account for most of the denials pharmacies see:

• Medicare Advantage confusion. A patient says "I have Medicare," but they're actually on a Medicare Advantage plan, so the claim needs to go to that plan, not to Original Medicare.
• Patient name, date of birth, or Medicare Beneficiary Identifier mismatches. Small differences from what's on file with Medicare are a leading cause of failed eligibility checks and rejected claims.
• Missing modifier 59 on same-day flu and COVID-19 administration.
• A Part D vaccine billed to Part B, or the reverse.
• A second flu shot in the same season billed without documentation of medical necessity.

Most of these trace back to the same root cause, confirming coverage and matching the information on file.

When the pharmacy benefit is the better path

Some situations call for billing through the patient's pharmacy (drug) benefit instead of a Part B medical claim:

• The patient has a Medicare Advantage plan that processes vaccines through the pharmacy benefit at the point of sale.
• The vaccine is a Part D vaccine, like Shingrix, RSV, or Tdap.
• Part B enrollment for the pharmacy isn't active yet, and the patient has drug coverage that will pay in the meantime.

It's worth collecting the patient's drug benefit card (BIN, PCN, group, and member ID) at intake even when you expect to bill Part B. If the medical claim doesn't go through, that card is the fallback and you'll already have the information in hand instead of tracking the patient down later.

What this looks like with MedMe

Pharmacies running Medicare Part B billing through MedMe get a few things built in: claims price automatically against your fee schedule, so there's no rate lookup to do by hand. Claims are submitted with assignment accepted, which is what keeps these vaccines at $0 for the patient. Real-time eligibility checks confirm active Part B coverage before you bill, and every claim is tracked from submission through payment so denials get caught early instead of surfacing weeks later during reconciliation.

For your team, that means fewer surprises at flu season volume and more time spent vaccinating patients instead of chasing down claims.

Frequently asked questions

Get your pharmacy ready before flu season peaks

Coding rules and coverage details are only useful once your pharmacy's billing setup is actually in place: Medicare enrollment, NPIs on file, and a payer connection that can submit claims electronically. If any of that isn't sorted yet, flu season is the wrong time to find out the hard way.

We put together a step-by-step guide to getting started with medical billing, covering what to set up, what to collect from patients, and how to avoid the mistakes that stall a pharmacy's first claims.