By Marc Gilman
(800) 927-9326 |
Mount Sinai Health System in New York City recently stopped accepting new patients under several public insurance plans, including Medicare Advantage dual-eligible coverage through Fidelis and Wellcare. It’s a New York story, tied to a specific contract dispute — but the underlying situation isn’t unique to New York at all. Hospital systems and Medicare Advantage plans renegotiate contracts every year, and when they don’t reach an agreement, patients are the ones caught in the middle. What actually happens to your coverage when that occurs is governed by federal rules that apply no matter which state you’re in.
Key Takeaways:
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Medicare Advantage plans generally must give you 30 days’ written notice before a provider you see regularly is terminated from the network.
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The “90-day continuity of care rule” is one of the most misunderstood protections in Medicare Advantage. It applies when you enroll in a new plan while already in active treatment — it doesn’t automatically kick in just because a provider leaves your current plan mid-year.
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Losing an entire hospital or health system carries more weight than losing a single doctor. CMS evaluates whether a network change is “significant” case by case, and a significant change can open a Special Enrollment Period to switch plans.
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If a significant network change pushes you back to Original Medicare, you get a real, valuable window — a 63-day Medigap guaranteed-issue right, meaning you can enroll in a Medigap policy without medical underwriting.
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Dual-eligible beneficiaries have their own separate monthly Special Enrollment Period, making it easier to move to a different Dual-Eligible Special Needs Plan if their current one loses an important provider.
What Just Happened With Mount Sinai, and Why It’s Worth Knowing About Even If You’re Not in NYC
As of August 1, 2026, Mount Sinai stopped accepting new patients — those who hadn’t been seen by a Mount Sinai provider since mid-2025 — under certain Fidelis and EmblemHealth plans, including Fidelis’s Wellcare-branded Medicare Advantage dual-eligible plans. Existing patients weren’t affected, and there were limited exceptions for things like ongoing transplant care. This followed an earlier, larger dispute between Mount Sinai and Anthem that took the health system out-of-network for Anthem’s Medicare Advantage and Marketplace plans for several months before a new agreement restored access in April.
None of this is unique to New York. Hospital-insurer contract disputes happen regularly across the country, and Medicare Advantage networks change every year, sometimes mid-year. The specific plans and hospital in this story are local, but the rules that determine what happens to a Medicare Advantage member caught in a network change like this are federal, and they apply the same way regardless of which state you’re in.
What Are Medicare Advantage Plans Actually Required to Tell You?
Federal regulations require Medicare Advantage plans to make a good-faith effort to notify affected members in writing at least 30 days before a contracted provider’s termination takes effect, when that provider has been seeing the member on a regular basis. The notice is supposed to identify the provider, the effective termination date, and how to find an in-network alternative. If a notice never arrives, or arrives with very little time to act, it’s worth documenting exactly when you found out and raising that directly with the plan, since this requirement exists specifically to prevent members from being blindsided.
Does the “90-Day Rule” Protect You If Your Doctor Leaves Your Plan?
This is the part people get wrong most often. The federal 90-day continuity of care rule applies when you enroll in a new Medicare Advantage plan while you’re already in an active course of treatment — chemotherapy, post-surgical recovery, and similar situations. During that 90-day window, the new plan generally can’t require prior authorization for the treatment you were already receiving. What it does not do is automatically protect you just because a provider leaves your current plan’s network mid-year. That’s a different situation, and it’s governed by the notice and Special Enrollment Period rules discussed below, not the continuity of care provision. Many plans will still work with members informally to avoid disrupting active treatment, but that’s a courtesy in that specific scenario, not a guaranteed federal right the way it is when you’re newly enrolling.
When Does a Network Change Qualify You for a Special Enrollment Period?
CMS evaluates this case by case, and the scale of what’s lost matters. A single primary care physician or specialist leaving the network generally doesn’t, on its own, meet the bar for a “significant” network change. Losing an entire hospital, health system, or a large share of a plan’s specialists in a given area is much more likely to qualify — especially if there’s no comparable in-network alternative nearby. If CMS determines a change is significant, affected members become eligible for a Special Enrollment Period to switch to a different plan outside the normal enrollment windows. Because this determination isn’t automatic, the reliable way to find out is to call your plan or 1-800-MEDICARE directly and ask whether your specific situation qualifies, rather than assuming either way. It’s also worth knowing that CMS has proposed changes that would make this SEP available more broadly, without requiring the “significant” determination at all — a change that, if finalized, would make switching easier for anyone affected by a provider termination, not just those affected by a large-scale network change.
What Happens If You Want to Go Back to Original Medicare?
This is a genuinely valuable, often-overlooked protection. If you lose Medicare Advantage coverage because your plan terminates, leaves your area, or undergoes a CMS-confirmed significant network change, and you decide to move back to Original Medicare, federal law gives you a Medigap guaranteed-issue right lasting 63 days after your Medicare Advantage coverage ends. During that window, you can enroll in a Medigap policy without medical underwriting — insurers can’t decline you or charge more based on your health. That’s a real opportunity, but it depends on paperwork: save the notice you received and its envelope, since that’s your proof of eligibility, and note the exact date your Medicare Advantage coverage actually ends, since that date anchors the 63-day window.
What About Dual-Eligible Beneficiaries Specifically?
If you’re enrolled in both Medicare and Medicaid, you have an additional layer of flexibility that other Medicare Advantage members don’t. CMS has established a monthly Special Enrollment Period specifically for full-benefit dual-eligible beneficiaries, letting them switch to a different Dual-Eligible Special Needs Plan essentially any time, not just during standard enrollment windows. If a network change affects a Dual-Eligible Special Needs Plan you’re enrolled in — the exact scenario in the Fidelis/Wellcare situation — this monthly SEP is generally the most direct path to changing plans without waiting for the fall enrollment period.
Where Does Insurance Planning Fit In?
Whether a given network change actually affects you, and what your best move is if it does, depends on which specific providers you rely on, whether the change meets CMS’s bar for “significant,” and whether Original Medicare with a Medigap policy or a different Medicare Advantage plan better fits your situation. None of that is something to guess at from a notice letter alone — it’s worth an actual conversation about your specific coverage and providers before assuming you know where you stand.
What To Do Next
If you’ve received a notice about a provider leaving your network, or you’re not sure whether a change like the Mount Sinai situation could affect coverage you’re counting on, we’re glad to help you sort out what it actually means for you. Call us at (800) 927-9326 or email — no pressure, just straight answers.
By Marc Gilman, Gilman Agency
This information is general in nature and not intended as legal or medical advice. Medicare Advantage network changes, notice requirements, and enrollment rights are governed by federal regulation and are subject to change. Confirm your specific situation directly with your plan or 1-800-MEDICARE.
Sources: Politico, “Mount Sinai stops taking some new patients on public insurance” (August 19, 2026); 42 CFR § 422.111(e) and § 422.62(b)(23), Medicare Advantage provider notification and Special Enrollment Period regulations; Centers for Medicare & Medicaid Services, 2024 Medicare Advantage and Part D Final Rule (CMS-4201-F); Centers for Medicare & Medicaid Services, CY 2027 Medicare Advantage and Part D Proposed Rule; U.S. News & World Report, “How to Change Your Medicare Plan: 2026 Guide to Deadlines & SEPs.”
