Switch Advantage Plans in October and the New Plan Cannot Require Reauthorization for Your Active Treatment for 90 Days. After That, Its Own Rules Can Take Over
Switching Medicare Advantage plans mid-treatment triggers a federal rule most enrollees never hear about, and the date that protection quietly expires may matter more than any premium comparison you run this October.
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A 68-year-old on monthly biologic infusions for rheumatoid arthritis spots a $0-premium Medicare Advantage plan during October’s Annual Enrollment Period and weighs it against the $38 she pays now. What the comparison page doesn’t show her is the federal rule that governs her first three months on the new plan, or the date that protection runs out.
This matters most if you’re mid-treatment on something a clinician administers: chemotherapy, biologic infusions, post-transplant regimens, injectable specialty drugs given in a clinic. If your prescriptions are stable generics from a chain pharmacy, the stakes here are lower and you can shop mostly on premium and network.
What the Rule Actually Says
Under code 42 CFR §422.112(b)(8), a Medicare Advantage plan must provide a minimum 90-day transition period for a new enrollee in an active course of treatment. During that window it cannot require prior authorization for that course of care, and that holds even when the treating provider is out of the new plan’s network. Two details matter more than the headline number.
The protection runs for the shorter of 90 days or the remainder of your active course of treatment. If your course finishes in six weeks, the shield ends with it. And it isn’t a blanket suspension of oversight. The plan can’t force reauthorization, but it can still conduct concurrent and retrospective review and apply coverage criteria it’s permitted to apply. “No reauthorization” is narrower than “nobody’s looking.” One more thing worth knowing, because it changes what you have to do: the protection applies whether or not your previous plan ever issued an authorization. You aren’t claiming a right. You already have it.
The Date to Circle
Annual Enrollment runs October 15 through December 7, and a plan change made in that window takes effect January 1. For coverage beginning January 1, 2027, March 31 is day 90 and April 1 is day 91. After that minimum period ends, the plan may reassess medical necessity, require prior authorization, and direct your care into its own network. It doesn’t have to do any of that on April 1 specifically. The point isn’t that something happens that morning. It’s that nothing stops it from happening after.
When the review does come, it may land on things that were never in question before. The plan may prefer a biosimilar over the branded biologic. It may require a different preferred infusion site. It may apply step therapy requiring documented failure on a cheaper alternative first. All of that can be legitimate under Medicare rules and still upend a regimen that was working.
Part D Runs on a Different Clock
If part of your treatment is a Part D drug rather than a clinician-administered Part B infusion, §422.112(b)(8) doesn’t cover it. Part D has its own transition rule under §423.120, and it works differently: it generally provides a temporary supply during your first 90 days, not blanket coverage for the period. That distinction decides which document you need to read. Part B infusions turn on the plan’s medical policy and network. Part D drugs turn on the formulary, and a formulary exception is the tool for that side.
What the $0 Premium Doesn’t Tell You
For someone mid-treatment, premium is close to the least useful number on the comparison page. What matters is whether the new plan covers your infusion at your current site, whether your infusion center and prescribing rheumatologist are in network, and what its site-of-care policy actually requires. The in-network out-of-pocket maximum caps your medical cost-sharing but excludes Part D drug spending, which carries its own separate cap. And a $0-premium plan still sits on top of the Part B premium, $202.90 in 2026, with the $283 Part B deductible underneath it.
Good News, Bad News
The protection is automatic, which is the good news and the trap. Don’t expect anybody at the new plan to call in January to confirm it applies to you, or someone to call in March to tell you it’s ending. Staying ahead of it starts in October:
- Before you enroll, pull the new plan’s 2027 medical policy and network list. Confirm your drug, your dose and your infusion site. If the plan already prefers a different site or requires step therapy, you may meet that later once the transition comes to a close.
- In January, notify the plan in writing and document your active treatment. You aren’t requesting permission, you’re creating a record. Attach your current authorization and your prescriber’s notes so nobody has to reconstruct this later.
- Also in January, ask when the plan will accept a prior-authorization request for care after March 31. Then have your prescriber submit it as early as the plan allows. If the answer is a denial or a modification, you want the appeal running while you still have coverage.
If the new plan turns out to be wrong for you, the Medicare Advantage Open Enrollment Period from January 1 to March 31 lets you move to another Advantage plan or back to Original Medicare. Returning usually means applying for Medigap under medical underwriting, and in most states you can be denied or rated up, though limited trial rights exist for some first-time Advantage enrollees. Ninety days is real protection. It’s also a bridge, not a destination, and bridges are easier to cross when you know where they end.
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Gerelyn Terzo is the author of dividend investing handbook "Dividend Investing Strategies: How to Have Your Cake & Eat It Too." A veteran financial journalist, she covers agri-finance for outlets like Global AgInvesting and the broader stock market and personal finance for 24/7 Wall Street. She began at CNBC and later helped launch Fox Business in New York. Gerelyn currently resides in Woodland Park, Colorado and dabbles in nature photography as a hobby.
